Content:

PS – Planetary & Solar System Sciences

PS1.1 – Rocky planets around the Sun and other stars – bulk, interiors, atmospheres, and their interdependent evolution

EGU21-3272 | vPICO presentations | PS1.1 | Highlight

Interpreting exoplanet biosignatures with a coupled atmosphere-interior-geochemical evolution model

Joshua Krissansen-Totton, Jonathan Fortney, Francis Nimmo, and Nicholas Wogan

The atmospheric evolution of rocky planets is shaped by a range of astrophysical, geophysical, and geochemical processes. Interpreting observations of potentially habitable exoplanets will require an improved understanding of how these competing influences interact on long timescales. In particular, the interpretation of biosignature gases, such as oxygen, is contingent upon understanding the probable redox evolution of lifeless worlds. Here, we develop a generalized model of terrestrial planet atmospheric evolution to anticipate and interpret future observations of habitable worlds. The model connects early magma ocean evolution to subsequent, temperate geochemical cycling. The thermal evolution of the interior, cycling of carbon-hydrogen-oxygen bearing volatiles, surface climate, crustal production, and atmospheric escape are explicitly coupled throughout this evolution. The redox evolution of the atmosphere is controlled by net planetary oxidation via the escape of hydrogen to space, the loss of atmospheric oxygen to the magma ocean, and oxygen consumption via crustal sinks such as outgassing of reduced species, serpentinization reactions, and direct “dry” oxidation of fresh crust.

The model can successfully reproduce the atmospheric evolution of a lifeless Earth: it consistently predicts an anoxic atmosphere and temperate surface conditions after 4.5 Gyrs of evolution. This result is insensitive to model uncertainties such as the details of atmospheric escape, mantle convection parameterizations, initial radiogenic inventories, mantle redox, the efficiency of crustal oxygen sinks, and unknown carbon cycle and deep-water cycle parameters. This suggests abundant oxygen is a reliable biosignature for literal Earth twins, defined as Earth-sized planets at 1 AU around sunlike stars with 1-10 Earth oceans and less initial carbon dioxide than water.

However, if initial volatile inventories are permitted to vary outside these “Earth-like” ranges, then dramatically different redox evolution trajectories are permitted. We identify three scenarios whereby Earth-sized planets in the habitable zones of sunlike stars could accumulate oxygen rich atmospheres (0.01 - 10 bar) in the absence of life. Specifically, (i) high initial CO2:H2O endowments, (ii), >50 Earth ocean water inventories, or (iii) extremely volatile poor initial inventories, could all result in oxygen-rich atmospheres after 4.5 Gyrs of evolution. These false positives arise despite the assumption that there is always sufficient non-condensible atmospheric gases, N2, to maintain an effective cold trap. Fortunately, all three oxygen false positive scenarios could potentially be identified by thorough characterization of the planetary context, such as from using time resolved photometry to constrain surface water inventories.

The model also sheds light on the atmospheric evolution of Venus and Venus-like exoplanets. We can successfully recover the modern state of Venus’ atmosphere, including a dense CO2-dominated atmosphere with negligible water vapor and molecular oxygen. Moreover, there is a clear dichotomy in the evolutionary scenarios that recover modern Venus conditions, one in which Venus was never habitable and perpetually in runaway greenhouse since formation, and another whereby Venus experienced ~1-2 Gyr of surface habitability with a ~100 m deep ocean. We explore the likelihood of each scenario and suggest future in situ observations that could help discriminate between these two alternative histories.

How to cite: Krissansen-Totton, J., Fortney, J., Nimmo, F., and Wogan, N.: Interpreting exoplanet biosignatures with a coupled atmosphere-interior-geochemical evolution model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3272, https://doi.org/10.5194/egusphere-egu21-3272, 2021.

EGU21-4617 | vPICO presentations | PS1.1

Impact of the measured parameters of exoplanets on the inferred internal structure.

Jon Fernandez Otegi, Caroline Dorn, Ravit Helled, François Bouchy, Jonas Haldemann, and Yann Alibert

Exoplanet characterization is one of the main foci of current exoplanetary science. For super-Earths and sub-Neptunes, we mostly rely on mass and radius measurements, which allow us to derive the mean density of the body and give a rough estimate of the bulk composition of the planet. However, the determination of planetary interiors is a very challenging task. In addition to the uncertainty in the observed fundamental parameters, theoretical models are limited owing to the degeneracy in determining the planetary composition.
 We aim to study several aspects that affect the internal characterization of super-Earths and sub-Neptunes: observational uncertainties, location on the M-R diagram, impact of additional constraints such as bulk abundances or irradiation, and model assumptions.
 We used a full probabilistic Bayesian inference analysis that accounts for observational and model uncertainties. We employed a nested sampling scheme to efficiently produce the posterior probability distributions for all the planetary structural parameter of interest. We included a structural model based on self-consistent thermodynamics of core, mantle, high-pressure ice, liquid water, and H-He envelope. 
 Regarding the effect of mass and radius uncertainties on the determination of the internal structure, we find three different regimes: below the Earth-like composition line and above the pure-water composition line smaller observational uncertainties lead to better determination of the core and atmosphere mass, respectively; and between these regimes internal structure characterization only weakly depends on the observational uncertainties. We also find that using the stellar Fe/Si and Mg/Si abundances as a proxy for the bulk planetary abundances does not always provide additional constraints on the internal structure. Finally we show that small variations in the temperature or entropy profiles lead to radius variations that are comparable to the observational uncertainty. This suggests that uncertainties linked to model assumptions can eventually become more relevant to determine the internal structure than observational uncertainties.

How to cite: Fernandez Otegi, J., Dorn, C., Helled, R., Bouchy, F., Haldemann, J., and Alibert, Y.: Impact of the measured parameters of exoplanets on the inferred internal structure., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4617, https://doi.org/10.5194/egusphere-egu21-4617, 2021.

EGU21-3420 | vPICO presentations | PS1.1

Internal water storage capacity of terrestrial planets and the effect of hydration on the M-R relation

Oliver Shah, Ravit Helled, Yann Alibert, and Klaus Mezger

The discovery of low density exoplanets in the super-Earth mass regime suggests that ocean planets could be abundant in the galaxy. Understanding the chemical interactions between water and Mg-silicates or iron is essential for constraining the interiors of water-rich planets. Hydration effects have, however, been mostly neglected by the astrophysics community so far. As such effects are unlikely to have major impacts on theoretical mass-radius relations, this is justified as long as the measurement uncertainties are large. However, upcoming missions, such as the PLATO mission (scheduled launch 2026), are envisaged to reach a precision of up to ≈ 3% and ≈ 10% for radii and masses, respectively. As a result, we may soon enter an area in exoplanetary research where various physical and chemical effects such as hydration can no longer be ignored. We have constructed interior models for planets that include reliable prescriptions for hydration of the cores and mantles. These models can be used to refine previous results for which hydration has been neglected and to guide future characterization of observed exoplanets. We have developed numerical tools to solve for the structure of multi-layered planets with variable boundary conditions and compositions. Here we have considered three types of planets: dry interiors, hydrated interiors, and dry interiors plus surface ocean, where the ocean mass fraction corresponds to the mass fraction of the H2O equivalent in the hydrated case. We find H and OH storage capacities in the hydrated planets equivalent to 0 - 6 wt% H2O corresponding to up to ≈800 km deep ocean layers. In the mass range 0.1 ≤ M/M ≤ 3, the effect of hydration on the total radius is found to be ≤ 2.5%, whereas the effect of separation into an isolated surface ocean is ≤ 5 %. Furthermore, we find that our results are very sensitive to the bulk composition.

How to cite: Shah, O., Helled, R., Alibert, Y., and Mezger, K.: Internal water storage capacity of terrestrial planets and the effect of hydration on the M-R relation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3420, https://doi.org/10.5194/egusphere-egu21-3420, 2021.

EGU21-12909 | vPICO presentations | PS1.1

Chromium, Nickel and Iron as clues to the formation histories of exoplanetary bodies

Andrew Buchan, Amy Bonsor, Oliver Shorttle, Jon Wade, and John Harrison

We are now entering an era of rocky exoplanet detection. To determine whether an exoplanet is ‘Earth-like’, we must estimate not only its mass, radius and insolation, but also its geological composition. These geological constraints have wide ranging implications, not least for a planet’s subsequent evolution and habitability.

Polluted white dwarfs which have accreted fragments of planetary material provide a unique opportunity to probe exoplanetary interiors. We can also learn about their formation histories, including the geological process of core-mantle differentiation.

Cr, Ni and Fe behave differently during differentiation, depending on the conditions under which it occurs. This alters the Cr/Fe and Ni/Fe ratios in the core and mantle of differentiated bodies. The pressure inside the body is a key parameter, and depends on the body’s size.

In our work, we present a novel approach for modelling this behaviour and use it to gain crucial insight into the sizes of exoplanetary bodies which pollute white dwarfs.

How to cite: Buchan, A., Bonsor, A., Shorttle, O., Wade, J., and Harrison, J.: Chromium, Nickel and Iron as clues to the formation histories of exoplanetary bodies, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12909, https://doi.org/10.5194/egusphere-egu21-12909, 2021.

EGU21-14697 | vPICO presentations | PS1.1

Predicted bulk compositions and geodynamical properties of terrestrial exoplanets in the Solar neighbourhood

Rob Spaargaren, Haiyang Wang, Maxim Ballmer, Stephen Mojzsis, and Paul Tackley

Our knowledge of the physical, chemical, and mechanical (i.e., rheological) properties of terrestrial planets is based almost entirely on our Solar System. Terrestrial exoplanets, however, show a startling diversity compared to our local experience. This observation challenges our understanding of terrestrial planet formation and of the thermal and mechanical behaviour of such worlds, some of which are vastly different from our own. To better understand the range and consequences of exoplanetary diversity, we integrate results from astrophysical models and observations, geodynamical simulations, and petrological experiments. Terrestrial exoplanet modelling requires plausible constraints to be placed on bulk planet compositions; bulk composition modulates interior properties, including core size, mantle mineralogy, and mantle melting behaviour. This may in turn affect the interaction between the planet’s interior and atmosphere, and thereby impact its potential to host a biosphere. Bulk composition may leave a signature on the mass and composition of the atmosphere, which could be detected in the future.

Here, we constrain exoplanetary diversity in terms of bulk planet composition, based on observations of stellar abundances in the Solar neighbourhood. We apply the devolatilization/fractionation trend between a planet and its host star [Wang+, 2019], to stellar abundances from the Hypatia catalogue [Hinkel+, 2014]. After applying a simplified model of rock-metal differentiation, we predict bulk planet and bulk silicate compositions of hypothetical exoplanets in the habitable zones of nearby stars. We further select 20 end-member compositions that span the full range of hypothetical bulk compositions based on our analysis.

With the compositions of these 20 end-members and by assuming Earth-like planetary masses and radii, we infer mineralogy and density profiles, as well as physical properties (e.g., viscosity) of the mantle using thermodynamic model Perple_X [Connolly, 2005]. These profiles and physical properties are prescribed in geodynamical models of exoplanet mantle evolution. We use convection code StagYY [Tackley, 2008] to model mantle convection and surface tectonic behaviour in a 2D spherical annulus geometry. We find that mantle viscosity increases with decreasing Mg:Si ratio of mantle rocks, with strong effects on planetary cooling and the likelihood of plate tectonics. In turn, the propensity of plate tectonics regulates the heat and chemical exchange between mantle and crust, affecting surface conditions and, by extension, atmospheric composition. This establishes a link between interior composition and surface conditions, and shows the importance of studying this aspect of planetary diversity. We recommend our 20 suggested end-members of terrestrial exoplanet compositions for subsequent modelling work.

How to cite: Spaargaren, R., Wang, H., Ballmer, M., Mojzsis, S., and Tackley, P.: Predicted bulk compositions and geodynamical properties of terrestrial exoplanets in the Solar neighbourhood, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14697, https://doi.org/10.5194/egusphere-egu21-14697, 2021.

EGU21-15884 | vPICO presentations | PS1.1

On the importance of including devolatilized stellar abundances in determining the composition of rocky exoplanets

Fabian Seidler, Haiyang Wang, and Sascha Quanz

Since stars and their planets form from the same molecular clouds, stellar chemical composition can be informative, to first order, of planetary bulk chemistry. An important feature of terrestrial planets compared to their host stars is the depletion of volatiles, the most important being oxygen. Previous studies on planet interiors focus on the mass and radius constraints and/or the host stellar refractory elements (e.g. Fe, Si and Mg), neglecting devolatilisation and its impact on the final picture of planet mineralogy and structure. This work assesses to what extent the devolatilised stellar abundances reflect rocky planetary composition.  

We firstly test how the uncertainties associated with planetary mass and radius would affect the modelling results of core mass fraction – an important interior parameter. To do so, we choose the Sun-like star Kepler-21 (stellar abundance uncertainties <0.05 dex) as a case study and assume it hosts an Earth-mass-and-radius planet in its habitable zone. We then assign different levels of uncertainties to the mass and radius of the hypothetical planet, ranging from 0.1% to 20%. We find that with increasing uncertainty level, the modelling result of core mass fraction constrained by the devolatilised stellar abundances and mass and radius becomes identical with the core mass fraction constrained purely by the devolatilised stellar abundances. This reveals the increased modelling degeneracy with growing uncertainties in mass and radius measurements, but also the strong constraints placed by using the devolatilised stellar abundances.

We further investigate a sample of 12 confirmed exoplanets, which are all less than 10 Earth masses and 2 Earth radii – i.e. potentially terrestrial planets or super-Earths – and with the measured uncertainties in mass and radius respectively less than 35% and 10%. By comparing the prior and posterior distributions of mass and radius before and after introducing the devolatilised stellar abundances as another prior, we find that the posterior distributions of all samples, but 55 Cnc e and Kepler-107 c, can be sampled within the 2σ ranges of the prior distributions. For the two exceptional cases, it means that the devolatilised stellar abundances and the measured mass and radius are not compatible within the level of 2σ.

We also find a diverse distribution of the core mass fractions of the sample from 0% (i.e. coreless) up to 40%, which are consistent at the 2σ level with the core mass fractions purely constrained by mass and radius measurements (except Kepler-107 c and 55 Cnc e),  but are significantly constrained by adding the devolatilized stellar abundances. In contrast, the previous study for the similar sample shows nearly constant core mass fractions of ~ 30% based on the unaltered stellar abundances and by assuming 100% Fe sunk into the core (i.e. free of consideration of the oxidation state of the planets). We emphasise that to break the degeneracies of terrestrial-type exoplanet interior modelling, we must use well the currently available observables including planetary mass and radius and host stellar chemical compositions, but they must be viewed through the lens of planet formation  and the resulting devolatilization.

How to cite: Seidler, F., Wang, H., and Quanz, S.: On the importance of including devolatilized stellar abundances in determining the composition of rocky exoplanets, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15884, https://doi.org/10.5194/egusphere-egu21-15884, 2021.

EGU21-5920 | vPICO presentations | PS1.1

Late Accretion and the Origin of Water on Terrestrial Planets in the Solar System

Cédric Gillmann, Gregor Golabek, Sean Raymond, Paul Tackley, Maria Schonbachler, Veronique Dehant, and Vinciane Debaille

Terrestrial planets in the Solar system generally lack surface liquid water. Earth is at odd with this observation and with the idea of the giant Moon-forming impact that should have vaporized any pre-existing water, leaving behind a dry Earth. Given the evidence available, this means that either water was brought back later or the giant impact could not vaporize all the water.

We have looked at Venus for answers. Indeed, it is an example of an active planet that may have followed a radically different evolutionary pathway despite the similar mechanisms at work and probably comparable initial conditions. However, due to the lack of present-day plate tectonics, volatile recycling, and any surface liquid oceans, the evolution of Venus has likely been more straightforward than that of the Earth, making it easier to understand and model over its long term evolution.

Here, we investigate the long-term evolution of Venus using self-consistent numerical models of global thermochemical mantle convection coupled with both an atmospheric evolution model and a late accretion N-body delivery model. We test implications of wet and dry late accretion compositions, using present-day Venus atmosphere measurements. Atmospheric losses are only able to remove a limited amount of water over the history of the planet. We show that late accretion of wet material exceeds this sink. CO2 and N2 contributions serve as additional constraints.

Water-rich asteroids colliding with Venus and releasing their water as vapor cannot explain the composition of Venus atmosphere as we measure it today. It means that the asteroidal material that came to Venus, and thus to Earth, after the giant impact must have been dry (enstatite chondrites), therefore preventing the replenishment of the Earth in water. Because water can obviously be found on our planet today, it means that the water we are now enjoying on Earth has been there since its formation, likely buried deep in the Earth so it could survive the giant impact. This in turn suggests that suggests that planets likely formed with their near-full budget in water, and slowly lost it with time.

How to cite: Gillmann, C., Golabek, G., Raymond, S., Tackley, P., Schonbachler, M., Dehant, V., and Debaille, V.: Late Accretion and the Origin of Water on Terrestrial Planets in the Solar System, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5920, https://doi.org/10.5194/egusphere-egu21-5920, 2021.

EGU21-2628 | vPICO presentations | PS1.1

Atmospheric Evolution due to impacts during the final stage of planet formation

Catriona Sinclair and Mark Wyatt

We investigate how the bombardment of terrestrial planets by populations of planetesimals left over from the planet formation process, asteroids from the main belt and comets affects the evolution of their atmospheres, through both impact induced atmospheric mass loss and volatile delivery. This work builds on previous studies of this topic by combining prescriptions for the atmosphere loss and mass delivery derived from hydrodynamic simulations with results from dynamical modelling of a realistic population of impactors.

 

The effect on the atmosphere predicted by the hydrodynamical simulations performed by Shuvalov (2009) as a function of the impactor and system properties are incorporated into a stochastic numerical model for the atmospheric evolution. The effects of rare but destructive giant impacts, that can cause non-local atmosphere loss, are also included using the prescription from Schlichting et al. (2015). The effects of aerial bursts and fragmentation of impactors in the atmosphere are included using a prescription based on the work of Shuvalov (2014). These effects are found to be relevant for hot and dense atmospheres analogous to the present day conditions on Venus.

 

We compare the impact induced atmosphere evolution of Earth, Venus and Mars using impact velocities and probabilities inferred from the results of dynamical models of the population of left over planetesimals in the early solar system from Morbidelli et al. (2018), the population of asteroids from Nesvorny et al. (2017a) and comets from Nesvorny et al. (2017b). We use realistic size distributions for these populations based on the main belt asteroids and trans-Neptunian objects. The effect of the variation in the distribution of the impactor material through their bulk density and volatile fraction is investigated, as is the effect of varying the initial conditions assumed for the atmospheres of Earth, Venus and Mars.

 

Our results for the Earth are discussed in light of observational constraints regarding the composition of the material delivered as the late veneer. The results for Venus and Mars are compared to those for the Earth and considered in comparison to observational evidence regarding the past climate of these worlds. A holistic view of the results for all three planets allows constraints on the past atmospheres to be inferred, in the absence of other atmospheric effects.

How to cite: Sinclair, C. and Wyatt, M.: Atmospheric Evolution due to impacts during the final stage of planet formation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2628, https://doi.org/10.5194/egusphere-egu21-2628, 2021.

EGU21-13084 | vPICO presentations | PS1.1

Thermal consequences of impact bombardments to silicate crusts of terrestrial-type exoplanets

Stephen J. Mojzsis and Oleg Abramov

Introduction. Post-accretionary impact bombardment is part of planet formation and leads to localized, regional [e.g., 1-3], or even wholesale global melting of silicate crust [e.g., 4]; less intense bombardment can also create hydrothermal oases favorable for life [e.g, 5]. Here, we generalize the effects of late accretion bombardments to extrasolar planets of different masses (0.1-10M). One example is Proxima Centauri b, estimated at ~2× M [6]. We model a 0.1M“mini-Earth”and “super-Earth” at 10M, the approximate upper limit for a “mini-Neptune” [7]. Output predicts lithospheric melting and subsurface habitable volumes.

Methods. The model [1,2] consists of (i) stochastic cratering; (ii) analytical thermal expressions for each crater [e.g., 8,9]; and (iii) a 3-D thermal model of the lithosphere, where craters cool by conduction and radiation.

We analyze impact bombardments using our solar system’s mass production functions for the first 500 Myr [10]. Surface temperatures and geothermal gradients are set to 20 °C and 70 °C/km [2]. Total delivered mass for Earth is 7.8 × 1021 kg, and scaled to other planets based on cross-sectional areas, with 1.7 × 1021 kg for mini-Earth, 1.2 × 1022 kg for Proxima Centauri b, and 3.6 × 1022 kg for super-Earth. The impactors' SFD is based on our main asteroid belt [11]. Impactor and target densities are set to 3000 kg m-3 and planetary bulk densities are assumed to be 5510 kg m-3, omitting gravitational compression [7]. Impactor velocity was estimated at 1.5 × vesc for each planet, with 7.8 km s-1 for mini-Earth,  16.8 km s-1 for the Earth, 21.1 km s-1 for Proxima Centauri b, and 36.1 km s-1 for super-Earth.

Results. We assume fully formed crusts, so melt volume immediately increases due to impacts. Super-Earth reaches a maximum of ~45% of the lithosphere in molten state, whereas mini-Earth reaches a maximum of only ~5%.  This is due to much higher impact velocities and cratering densities on the super-Earth compared to mini-Earth. We also show the geophysical habitable volumes within the upper 4 km of a planet’s crust as the bombardment progresses. Impacts sterilize the majority of the habitable volume on super-Earth; however, due to its large total volume, the total habitable volume is still higher than on other planets despite the more intense bombardment in terms of energy delivered per unit area.

References: [1] Abramov, O., and S.J. Mojzsis (2009) Nature, 459, 419-422. [2] Abramov et al. (2013) Chemie der Erde, 73, 227-248. [3] Abramov, O., and S. J. Mojzsis (2016) Earth Planet Sci. Lett., 442, 108-120. [4] Canup, R. M. (2004) Icarus, 168, 433-456. [5] Abramov, O., and D. A. Kring (2004) J. Geophys. Res., 109(E10). [6] Tasker, E. J. et al. (2020). Astronom. J., 159(2), 41. [7] Marcy, G. W. et al. (2014). PNAS, 111(35), 12655-12660. [8] Kieffer S. W. and Simonds C. H. (1980) Rev. Geophys. Space Phys., 18, 143-181. [9] Pierazzo E., and H.J. Melosh (2000). Icarus, 145, 252-261. [10] Mojzsis, S. J. et al. (2019). Astrophys. J., 881(1), 44. [11] Bottke, W. F. et al. (2010) Science, 330, 1527-1530.

How to cite: Mojzsis, S. J. and Abramov, O.: Thermal consequences of impact bombardments to silicate crusts of terrestrial-type exoplanets, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13084, https://doi.org/10.5194/egusphere-egu21-13084, 2021.

EGU21-13030 | vPICO presentations | PS1.1 | Highlight

Contributions of Volatiles to the Venus Atmosphere from the Observed Extrusive Volcanic Record: Implications for the History of the Venus Atmosphere

James Head, Lionel Wilson, Mikhail Ivanov, and Robin Wordsworth

One of the most important questions in planetary science is the origin of the current Venus atmosphere, its relationship and coupling to Venus’ geologic and geodynamic evolution, andwhy it is so different from that of the Earth. We specifically address the following question:Does the eruption of the total volume of extrusive volcanic deposits observed in the exposed geologic record of Venus contribute significantly to the current atmosphere through volatile release during emplacement of the extruded lavas? To address this question, we used the observed geologic and stratigraphic record of volcanic units and features, and their volumes, as revealed by Magellan (1; their Fig. 26 and Table 5).  We converted the volumes of the main volcanic units to lava/magma masses using a density of 3000 kg m-3. Next, we chose the upperthickness values, and added the contributions from allof the units; summing the values of the "total eruptives" gives the absolute upper limit estimate of the mass of documented volcanics that could contribute to the atmosphere, 7.335 x 1020 kg. We then compare this with the current mass of the Venus atmosphere (4.8 x 1020 kg). We find that in order to make the current atmosphere from the above volcanics, the magma would have to consist of 65.4% by mass volatiles, which is, of course, impossible. We conclude that the grand totalof the currently documented volcanics can not have produced other than a very small fraction of the current atmosphere.

Exsolution of volatiles during volcanic eruptions is significantly dependent on surface atmospheric pressure (2-3). However, the total volumeof lava erupted in the period of global volcanic resurfacingis still insufficient to produce the CO2atmosphere observed today, even if the ambient atmospheric pressure at that time was only 50% of what it is today. Therefore, a very significant part of the current CO2atmosphere must have been inherited from a time prior to the observed geologic record, sometime in the first ~80% of Venus history. Furthermore, the total volumeof lava erupted in the stratigraphically youngest period of the observed record (1) is insufficient to account for the current abundance of SOin the atmosphere; thus, it seems highly unlikely that current and recently ongoing volcanism could be maintaining the currently observed ‘elevated’ levels of SOin the atmosphere (4).  In addition, because of the fundamental effect of atmospheric pressure on the quantity of volatiles that will be degassed, varying the nature of the mantle melts over a wide range of magma compositions and mantle fOappears to have minimal influence on the outcome.  We conclude that the current Venus atmosphere must be a “fossil atmosphere”, largely inherited from a previous epoch in Venus history, and if so, may provide significant insight into the conditions during the first 80% of Venus history.

(1) Ivanov and Head (2013) Plan. Space Sci. 84, 66; (2) Gaillard & Scaillet, 2014, EPSL 403, 307; (3) Head & Wilson, 1986, JGR 91, 9407;(4)Esposito, 1984, Science 223, 1072.

How to cite: Head, J., Wilson, L., Ivanov, M., and Wordsworth, R.: Contributions of Volatiles to the Venus Atmosphere from the Observed Extrusive Volcanic Record: Implications for the History of the Venus Atmosphere, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13030, https://doi.org/10.5194/egusphere-egu21-13030, 2021.

EGU21-7311 | vPICO presentations | PS1.1

Thermal evolution of terrestrial planets with 2D and 3D geometries

Aymeric Fleury, Ana-Catalina Plesa, and Christian Hüttig

In mantle convection studies, two-dimensional geometry calculations are predominantly used, due to their reduced computational costs when compared to full 3-D spherical shell models.  Although various 3-D grid formulations [e.g. 1, 2] have been employed in studies using complex scenarios of thermal evolution [e.g., 3, 4], simulations with these geometries remain highly expensive in terms of computational power and thus 2-D geometries are still preferred in most of the exploratory studies involving broader ranges of parameters. However, these 2-D geometries still present drawbacks for modeling thermal convection. Although scaling and approximations can be applied to better match the average quantities obtained with 3D models [5], in particular, the convection pattern that in turn is critical to estimate melt production and distribution during the thermal evolution is difficult to reproduce with a 2D cylindrical geometry. In this scope, another 2D geometry called “spherical annulus” has been proposed by Hernlund and Tackley, 2008 [6]. Although steady state comparison between 2D cylindrical, spherical annulus and 3D geometry exist [6], so far no systematic study of the effects of these geometries in a thermal evolution scenario is available. 

In this study we implemented a 2-D spherical annulus geometry in the mantle convection code GAIA [7] and used it along 2-D cylindrical and 3-D geometries to model the thermal evolution of 3 terrestrial bodies, respectively Mercury, the Moon and Mars. 

First, we have performed steady state calculations in various geometries and compared the results obtained with GAIA with results from other mantle convection codes [6,8,9]. For this comparison we used several scenarios with increasing complexity in the Boussinesq approximation (BA).

In a second step we run thermal evolution simulations for Mars, Mercury, and the Moon using GAIA with 2D scaled cylinder, spherical annulus and 3D spherical shell geometries.In this case we considered the extended Boussinesq approximation (EBA), an Arrhenius law for the viscosity, a variable thermal conductivity between the crust and the mantle, while taking into account the heat source decay and the cooling of the core, as appropriate for modeling the thermal evolution. A detailed comparison between all geometries and planets will be presented focussing on the convection pattern and melt production. In particular, we aim to determine which 2D geometry reproduces most accurately the results obtained in a 3D spherical shell model. 

Aknowledgments: The authors gratefully acknowledges the financial support and endorsement from the DLR Management Board Young Research Group Leader Program and the Executive Board Member for Space Research and Technology.

References: [1] Kageyama and Sato, G3, 2004; [2] Hüttig and Stemmer, G3, 2008;  [3] Crameri & Tackley, Progress Planet. Sci., 2016; [4] Plesa et al., GRL (2018); [5] Van Keken, PEPI, 2001; [6] Hernlund and Tackley, PEPI, 2008; [7] Hüttig et al, PEPI 2013; [8] Kronbichler et al., GJI, 2012; [9]  Noack et al., INFOCOMP 2015.

How to cite: Fleury, A., Plesa, A.-C., and Hüttig, C.: Thermal evolution of terrestrial planets with 2D and 3D geometries, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7311, https://doi.org/10.5194/egusphere-egu21-7311, 2021.

EGU21-8910 | vPICO presentations | PS1.1

Exploring the convection in super-Earths: Comparing LHS 3844b with 55 Cnc e

Tobias G. Meier, Dan J. Bower, Tim Lichtenberg, Paul J. Tackley, and Brice-Olivier Demory

The vigour and style of mantle convection in tidally-locked super-Earths may be substantially different from Earth's regime where the surface temperature is spatially uniform and sufficiently cold to drive downwellings into the mantle. The thermal phase curve for super-Earth LHS 3844b suggests a solid surface and lack of a substantial atmosphere. The dayside temperature is around 1040 K and the nightside temperature is around 0 K, which is unlike any temperature contrast observed at present day for planets in the Solar System. On the other hand, the thermal phase curve of super-Earth 55 Cnc e suggests much hotter temperatures with a nightside temperature around 1380 K and a substellar point temperature around 2700 K. Both super-Earths have therefore temperature contrasts between the day- and nightside of more than 1000 K and we infer that this may also lead to a dichotomy of the interior mantle flow. 
We run geodynamic simulations of the interior mantle flow using the mantle convection code StagYY. The models are fully compressible with an Arrhenius-type viscosity law where the mantle is modelled with an upper mantle, a perovskite-layer and a post-perovskite layer. The lithospheric strength is modelled through a plastic yielding criteria and the heating mode is either basal heating only or mixed heating (basal and internal heating). For LHS 3844b we find that the surface temperature dichotomy can lead to a hemispheric tectonic regime depending on the strength of the lithosphere and the heating mode in the mantle. In a hemispheric tectonic regime, downwellings occur preferentially on one side and upwellings rise on the other side. We compare these results to the case of 55 Cnc e, where large parts of the surface could be molten. At first order we expect that a magma ocean could homogenise the temperatures on the planet's surface and therefore reduce the likelihood of hemispheric tectonics operating on 55 Cnc e.
For LHS 3844b, the contribution of the interior flux to the thermal phase curve is on the order of 15-30 K, and therefore below the detecting capabilities of current and near-future observations. However, for hemispheric tectonics, upwellings might lead to preferential melt generation and outgassing on one hemisphere that could manifest as a secondary signal in phase curve observations. Such signals could also be produced on hotter planets such as 55 Cnc e where parts of the surface are hot enough to melt.

How to cite: Meier, T. G., Bower, D. J., Lichtenberg, T., J. Tackley, P., and Demory, B.-O.: Exploring the convection in super-Earths: Comparing LHS 3844b with 55 Cnc e, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8910, https://doi.org/10.5194/egusphere-egu21-8910, 2021.

EGU21-2299 | vPICO presentations | PS1.1

Interior heating and outgassing of Proxima Cen b: Identification of critical parameters

Lena Noack, Kristina Kislyakova, Colin Johnstone, Manuel Güdel, and Luca Fossati

Since the discovery of a potentially low-mass exoplanet around our nearest neighbour star Proxima Centauri, several works have investigated the likelihood of a shielding atmosphere and therefore the potential surface habitability of Proxima Cen b. However, outgassing processes are influenced by several different (unknown) factors such as the actual planet mass, mantle and core composition, and different heating mechanisms in the interior.
We aim to identify the critical parameters that influence the mantle and surface evolution of the planet over time, as well as to potentially constrain the time-dependent input of volatiles from mantle into the atmosphere.


To study the coupled star-planet evolution, we analyse the heating produced in the interior of Proxima Cen b due to induction heating, which strongly varies with both depth and latitude. We calculate different rotation evolutionary tracks for Proxima Centauri and investigate the change in its rotation period and magnetic field strength. Unlike the Sun, Proxima Centauri possesses a very strong magnetic field of at least a few hundred Gauss, which was likely higher in the past. 
We apply an interior structure model for varying planet masses (derived from the unknown inclination of observation of the Proxima Centauri system) and iron weight fractions, i.e. different core sizes, in the range of observed Fe-Mg variations in the stellar spectrum. 
We use a mantle convection model to study the thermal evolution and outgassing efficiency of Proxima Cen b. For unknown planetary parameters such as initial conditions we chose randomly selected values. We take into account heating in the interior due to variable radioactive heat sources and latitute- and radius-dependent induction heating, and compare the heating efficiency to tidal heating.


Our results show that induction heating may have been significant in the past, leading to local temperature increases of several hundreds of Kelvin (see Fig. 1). This early heating leads to an earlier depletion of the interior and volatile outgassing compared to if the planet would not have been subject to induction heating. We show that induction heating has an impact comparable to tidal heating when assuming latest estimates on its eccentricity. We furthermore find that the planet mass (linked to the planetary orbital inclination) has a first-order influence on the efficiency of outgassing from the interior.

 

 

Fig 1: Local induction heating and resulting temperature variations compared to a simulation without induction heating after 1 Gyr of thermal evolution for an example rocky planet of 1.8 Earth masses with an iron content of 20 wt-%.

How to cite: Noack, L., Kislyakova, K., Johnstone, C., Güdel, M., and Fossati, L.: Interior heating and outgassing of Proxima Cen b: Identification of critical parameters, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2299, https://doi.org/10.5194/egusphere-egu21-2299, 2021.

EGU21-4011 | vPICO presentations | PS1.1

Early Mercury’s magma ocean atmosphere

Noah Jäggi, Diana Gamborino, Dan J. Bower, Paolo Sossi, Aaron Wolf, Audrey Vorburger, Apurva V. Oza, Peter Wurz, and André Galli

The large iron core of Mercury and the low iron contents on the surface inferred from MESSENGER data suggest the presence of a magma ocean after accretion. We modeled the lifetime of an early Hermean magma ocean as well as the structure and loss rates of an atmosphere that is sourced by degassing. We use a large range of initial conditions including several bulk compositions associated with varying degrees of differentiation, the inclusion of carbon and hydrogen degassing volatiles such as CO2 and H2O, as well as considering a larger proto-Mercury size. After obtaining the magma ocean lifetime and volatile vapor pressures, the result is passed on to further models to obtain metal oxide vapor pressures, a complete atmospheric photochemical speciation and ultimately the mass loss rate of the atmosphere.

We show that magma ocean cooling times are sensitive to the size of the planet and the efficiency of radiative heat transfer in the atmosphere. A volatile-free proto-Mercury radiating as a blackbody with its present-day size would cool down within 400 years from an assumed initial surface temperature of 2500 K to an early crust formation threshold of 1500 K. In contrast it takes 9000 years for a volatile rich proto-Mercury with a greenhouse atmosphere and a mantle size representing Mercury before the occurrence of a mantle stripping event. Volatile-rich cases reach massive atmosphere pressures, whereas volatile-free cases are dominated by Si, Na, K, Mg, and Fe species degassed from the magma ocean and end up at a maximum pressure of 0.1 bar at 2500 K. There is however only a small difference in the atmospheric extent, as the absence of volatile species in the thin metal oxide atmosphere causes it to become extended to a degree, where an upper atmosphere height comparable to the volatile cases is reached. In terms of mass loss we found that upper atmospheric loss due to photoionization is highly efficient in the environment of a young Sun, ionizing 100% of the particles reaching Mercury’s exosphere. This leads to loss rates of up to 106 kg/s, which are however diffusion limited by the supply from the homopause, reducing them by 2-3 orders of magnitude. In regards to Na and K loss, we found that a thin, volatile-free atmosphere is most efficient with its extended structure allowing for large loss rates as well as the high Na and K mixing ratio.

How to cite: Jäggi, N., Gamborino, D., Bower, D. J., Sossi, P., Wolf, A., Vorburger, A., Oza, A. V., Wurz, P., and Galli, A.: Early Mercury’s magma ocean atmosphere, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4011, https://doi.org/10.5194/egusphere-egu21-4011, 2021.

EGU21-9745 | vPICO presentations | PS1.1

From clouds to crust - Cloud diversity and surface conditions in atmospheres of rocky exoplanets

Oliver Herbort, Peter Woitke, Christiane Helling, and Aubrey Zerkle

One of the fundamental questions for planetary science is how surfaces of other planets similar to the rocky bodies in our solar system look like. What is the rock structure like? Will there be water? Are there any active atmospheric cycles? How can these different conditions be detected?

The current space missions and ground based instruments allow the detection of specific gas species and some cloud compositions in atmospheres of giant exoplanets. With instruments  installed in the near future and space crafts currently being build or planned, these kind of observations will be available for planets with smaller sizes and an overall rocky composition. We aim to further understand the connection of the conditions of the upper atmosphere with the conditions on the crust of the planet (temperature, pressure, composition).

Our equilibrium chemistry models allow us to investigate the expected crust and near-crust-atmosphere composition. With this, we investigate the conditions under which liquid water is actually stable at the surface of a planet and not incorporated in hydrated rocks. Based on this crust - near-crust-atmosphere interaction we build an atmospheric model, which allows us to investigate what kind of clouds are stable and could be present in atmospheres of rocky exoplanets. This allows us to predict what clouds on other planets could be made of. Potential detection of cloud condensates and the high altitude gas phase can constrain the overall surface conditions on those planets. 

How to cite: Herbort, O., Woitke, P., Helling, C., and Zerkle, A.: From clouds to crust - Cloud diversity and surface conditions in atmospheres of rocky exoplanets, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9745, https://doi.org/10.5194/egusphere-egu21-9745, 2021.

EGU21-15422 | vPICO presentations | PS1.1

 The mechanisms of formation of some small cones in Chryse Planitia on Mars
not presented

Leszek Czechowski, Natalia Zalewska, Anita Zambrowska, Marta Ciazela, Piotr Witek, and Jan Kotlarz

Introduction: Small cones are common on Mars. Many cones form subparallel chains several kilometers in length. Their origin is discussed in many papers, however, the mechanism of their formation is not explained [1].

In the present paper, we deal with a small region in Chryse Planitia ( ~38o13′ N and ~319o25’ E). The region is covered by lacustrine deposits.

    On Mars, chains of small cones occupy vast areas. Therefore, we try to explain the existence of the chains by specific conditions on Mars. We focus on the hypothesis connecting the formation of cones with the loss of water from the regolith due its instability. See e.g. [1], [2], [4], [5].

 

Mechanism of cones formation: We consider 3 mechanisms of cone formation: (i) a grains’ ejection, (ii) from mud or fluidized sand and (iii) explosive formation. The (iii) and (ii) are possible with additional heat sources only.

    Assuming that only heat of melting was used for vaporization, then only ~13% of liquid water will be vaporized, If the outgassing effect is to be regolith without water, then there must be also other heat sources. Therefore we consider two coexisting factors required for cones formation: (1) the presence of water in the regolith and (2) some additional heating, e.g. magma intrusion.

    The formation of a chain of cones is possible in two situations:

(a) above a linear structure containing water and areal heating. Outcrops of aquifers could serve as linear sources of volatiles.

(b) above a linear source of magmatic heat and the areal aquifer. A dike could serve as linear source of heat.

 

Conclusions and future plans;

1) Considered cones could be a result of outgassing of regolith due to pressure drop.

2) Subparallel chains of cones were formed along the outcrops of volatile-rich sediments.

3) Numerical modeling indicates that small magma intrusions may not be enough for completely degassing some aquifers.

 

Acknowledgments: This study was supported by statutory project of Institute of Geophysics of University of Warsaw. We are also grateful to prof. W. Kofman and dr. J. Ciążela for their remarks.

 

References

[1] Fagents, S., Thordarson, T., (2007) The Geology of Mars: Evidence from Earth-Based Analogs, ed. Mary Chapman. Cambridge Univ. Press. [2] Brož,, et al. (2019) JGR: Planets. 124, 703–720. [3] Rotto, S., Tanaka, K. L. (1995) Geologic/ geomorphologic map of the Chryse Planitia: region of Mars. USGS. [4] Barlow, N.G. (2010) GSA Bulletin (2010) 122 (5-6): 644–657. [5] Brož, P., et al. (2020) Nature Geoscience. 13, 403–407.

How to cite: Czechowski, L., Zalewska, N., Zambrowska, A., Ciazela, M., Witek, P., and Kotlarz, J.:  The mechanisms of formation of some small cones in Chryse Planitia on Mars, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15422, https://doi.org/10.5194/egusphere-egu21-15422, 2021.

EGU21-5745 | vPICO presentations | PS1.1

Martian Dichotomy from a Giant Impact: Mantle Convection Models

Kar Wai Cheng, Paul J. Tackley, Antoine B. Rozel, Gregor J. Golabek, Harry Ballantyne, and Martin Jutzi

The Martian crustal dichotomy is one of the most prominent features on the planet, featuring a ≈5.5 km difference in topography and a ≈25 km difference in crustal thickness between the southern highland and northern lowland [1]. It Is thought to have formed within the first 400-500 Myr of Martian history [2]. While its formation process remains unclear, there have been different hypotheses to explain it, including an endothermic degree-1 convection mode [3, 4], and the excavation of the lowland crust by a giant impact [5]. In this study we focus on the hybrid hypothesis, where an early giant impact created a magma pond, and subsequent mantle convection alters the internal mantle structure as well as crustal distribution in the next 4 billion years [6, 7].  By imposing a parametrized giant impact as a thermal anomaly as an initial condition, we simulate the long-term evolution of the crust and mantle using the thermochemical convection code StagYY [8]. In particular, we investigate the effect of physical parameters of both the solid mantle and the impact-induced magma pond, as well as those of the crust production process, on the crystallisation of such pond, its interaction with surrounding mantle and the preservation of impact signature. Diagnostics including topography and crust thickness from these different models will be presented and compared.

 

[1] Watters, T., McGovern, P., & Irwin III, R. (2007). Hemispheres Apart: The Crustal Dichotomy on Mars. Annual Review of Earth and Planetary Sciences, 35(1), 621-652.

[2] Taylor, S., & McLennan, S. (2009). Planetary crusts. Cambridge, UK: Cambridge University Press.

[3] Roberts, J., & Zhong, S. (2006). Degree-1 convection in the Martian mantle and the origin of the hemispheric dichotomy. Journal of Geophysical Research, 111(E6).

[4] Keller, T., & Tackley, P. (2009). Towards self-consistent modeling of the martian dichotomy: The influence of one- ridge convection on crustal thickness distribution. Icarus, 202(2), 429-443.

[5] Andrews-Hanna, J., Zuber, M., & Banerdt, W. (2008). The Borealis basin and the origin of the martian crustal dichotomy. Nature, 453(7199), 1212-1215.

[6] Golabek, G., Keller, T., Gerya, T., Zhu, G., Tackley, P., & Connolly, J. (2011). Origin of the martian dichotomy and Tharsis from a giant impact causing massive magmatism. Icarus, 215(1), 346-357.

[7] Reese, C., Orth, C., & Solomatov, V. (2011). Impact megadomes and the origin of the martian crustal dichotomy. Icarus, 213(2), 433-442.

[8] Tackley, P. (2008). Modelling compressible mantle convection with large viscosity contrasts in a three- dimensional spherical shell using the yin-yang grid. Physics of The Earth and Planetary Interiors, 171(1-4), 7-18

 

 

How to cite: Cheng, K. W., Tackley, P. J., Rozel, A. B., Golabek, G. J., Ballantyne, H., and Jutzi, M.: Martian Dichotomy from a Giant Impact: Mantle Convection Models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5745, https://doi.org/10.5194/egusphere-egu21-5745, 2021.

EGU21-16023 | vPICO presentations | PS1.1

Identifying the Sweet Spot for an Impact-Induced Martian Dichotomy

Harry Ballantyne, Martin Jutzi, and Gregor J. Golabek

The martian crustal dichotomy predominantly refers to the 4-8 km difference in elevation between the southern hemisphere and an apparent basin covering roughly 42% of the north, with this topographical picture being strongly reflected in distribution of crust below. Other associated features include a higher density of volcanoes and visible impact craters in the south relative to the north.

Most studies attempting to explain these properties have supported one of two theories; either the dichotomy formed solely through geodynamic processes [1], or a giant impact occurred that imprinted the crustal cavity in the northern hemisphere that is observed today [2]. Recent work has proved the importance of coupling these hypotheses, introducing a hybrid exogenic-endogenic scenario whereby a giant impact triggered a localized magma ocean and subsequent superplume in the southern hemisphere [3]. This has, however, only been investigated using a very limited range of initial parameters, all of which lead to significant heating deep into the mantle. This therefore motivates an interesting area of study – is there a parameter space that leads to a hemispherically-thickened crust without significantly heating the mantle?

We aim to answer this question using a suite of smoothed-particle hydrodynamics (SPH) simulations, using the SPHLATCH code [4], that explore a large parameter-space chosen with the intention of limited internal heating. Each model includes the effects of shear strength and plasticity (via a Drucker-Prager-like yield criterion) as such effects have been shown to be significant on the scales concerned in this study [3,4]. Moreover, the sophisticated equation of state ANEOS is being used along with a Mars-specific solidus [5] to accurately calculate the physical environment in which such solid characteristics must be considered. For the analysis of the simulation outcomes we apply a newly developed scheme to estimate the thickness and distribution of (newly formed or re-distributed) post-impact crust.

Initial results have revealed promising hemispherical features in certain cases, with further analysis being made in an attempt to compare the results to those of the observational data in a quantitative manner (e.g. through bimodal fitting of crustal thickness histograms and k-means clustering). In addition, the effects of a uniform, primordial crust being present on Mars before the dichotomy-forming event are being studied, as well as an investigation into the final distribution of the impactor material as this could be chemically distinct from the primordial martian composition. Finally, the effects of material strength have been found to be non-negligible, further highlighting the importance of such aspects on the length-scales involved in planetary collisions.

 

References:

[1] Keller, T. and Tackley, P. J. (2009) Icarus, 202(2):429–443.

[2] Marinova, M. M., Aharonson, O., and Asphaug, E. (2008) Nature, 453(7199):1216–1219.

[3] Golabek, G. J., Emsenhuber, A., Jutzi, M., Asphaug, E. I., and Gerya, T. V. (2018) Icarus, 301:235–246.

[4] Emsenhuber, A., Jutzi, M., and Benz, W. (2018) Icarus, 301:247–257.

[5] Duncan, M. S., Schmerr, N. C., Bertka, C. M., and Fei, Y. (2018) Geophysical Research Letters, 45:10, 211–10,220.

How to cite: Ballantyne, H., Jutzi, M., and Golabek, G. J.: Identifying the Sweet Spot for an Impact-Induced Martian Dichotomy, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16023, https://doi.org/10.5194/egusphere-egu21-16023, 2021.

EGU21-3273 | vPICO presentations | PS1.1

A Lithology-based Silicate Weathering Model for Earth-like Planets

Kaustubh Hakim, Dan J. Bower, Meng Tian, Russell Deitrick, Pierre Auclair-Desrotour, Daniel Kitzmann, Caroline Dorn, Klaus Mezger, and Kevin Heng

Silicate weathering is a key step in the carbonate-silicate cycle (carbon cycle) that draws down

CO2 from the atmosphere for eventual burial and long-term storage in the planetary interior. This process is thought to provide an essential negative feedback to the carbon cycle to maintain temperate climates on Earth and Earth-like. We implement thermodynamics to determine weathering rates as a function of surface lithology (rock type). These rates provide upper limits that allow estimating the maximum rate of weathering in regulating climate. We model chemical kinetics and thermodynamics to determine weathering rates for three types of rocks inspired by the lithologies of Earth's continental and oceanic crust, and its upper mantle. We find that thermodynamic weathering rates of a continental crust-like lithology are about one to two orders of magnitude lower than those of a lithology characteristic of the oceanic crust. Our results show that the weathering of mineral assemblages in a given rock, rather than individual minerals, is crucial to determine weathering rates at planetary surfaces. We show that when the CO2 partial pressure decreases or surface temperature increases, thermodynamics rather than kinetics exerts a strong control on weathering. The kinetically- and thermodynamically-limited regimes of weathering depend on lithology, whereas, the supply-limited weathering is independent of lithology. Our results imply that the temperature-sensitivity of thermodynamically-limited silicate weathering may instigate positive feedback to the carbon cycle, in which the weathering rate decreases as the surface temperature increases. 

How to cite: Hakim, K., Bower, D. J., Tian, M., Deitrick, R., Auclair-Desrotour, P., Kitzmann, D., Dorn, C., Mezger, K., and Heng, K.: A Lithology-based Silicate Weathering Model for Earth-like Planets, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3273, https://doi.org/10.5194/egusphere-egu21-3273, 2021.

EGU21-2704 | vPICO presentations | PS1.1

The effects of graphite and particles size on reflectance spectra of silicates

Enrico Bruschini, Cristian Carli, Fabrizio Capaccioni, Mathieu Vincendon, Anne-Cécile Buellet, Francesco Vetere, Arianna Secchiari, Marco Ferrari, Diego Perugini, and Alessandra Montanini

Mercury is characterized by a globally low reflectance associated with remarkably low iron contents. Among several proposed hypothesis, to date, the most convincing explanation of the low reflectance of Mercury invokes mixing of an ancient graphite-rich crust with overlying volcanic materials via impact processes and/or assimilation of carbon into rising magmas during secondary crustal formation (e.g. Peplowski et al.2016). Even though until now graphite has not been directly observed, there are strong evidences suggesting its presence on Mercury’s surface (e.g. Denevi et al.2009; Peplowski et al.2011). The actual presence of graphite within Mercury soil may have several implications, e.g. on the late accretion history of Mercury (Hyodo et al.2021; Murchie et al.2015) or on hollow formation (Blewett et al.2016). Moreover, silicates are often associated to carbon phases in some achondrites (e.g. ureilite, Nestola et al.2020, and references therein). Evaluating in a systematic way the effect of graphite on visible and near-infrared spectroscopy of mafic mineral absorptions is thus of interest to improve our understanding of Mercury remote sensing data, and to make progress in our capability to associate carbon-rich stony meteorites to their parent bodies. Mixing graphite with silicate materials is thought to basically decrease the contrast of reflectance spectra of these materials (Murchie et al.2015). Nevertheless, systematic works addressing the influence of graphite-silicate mixtures on their reflectance spectra are still lacking. Here we mixed microcrystalline graphite with a suite of silicate materials and measured their VNIR reflectance spectra. We selected three silicate end-member compositions, namely: 1) a synthetic glass with chemical composition close to the one inferred for of the volcanic products emplaced in the Mercury’s northern volcanic plains (Vetere et al.2017), 2) a Mg-rich Gabbronorite with FeO < 3% (Secchiari et al.2018) and 3) a hawaiitic basalt (Pasquarè et al.2008). To decouple the effect of granulometry and graphite content, we produced and analyzed different granulometric classes (ranging between <50 μm and 250μm) for each end-member. In a second stage, we selected three granulometric classes (<50 μm, 75-100 μm and 150-180 μm) for each end member and we added graphite producing different samples with graphite – silicate weight ratio between 0-5% (0%, 1%, 2%, 3%, 4% and 5%) in order to encompass the inferred graphite content in Mercury’s surface (Klima et al.2018). The results of our work confirm that graphite strongly decreases the contrast of the reflectance spectra of the silicate-graphite mixtures and, in most cases, has a negligible effect on the shift of the absorption bands. However the slopes of the reflectance spectra are greatly affected by the graphite content, which tends to decrease the slope of the spectra. Our systematic study will allow to gain a better understanding of the reflectance spectra of materials mixed with opaque phases in meteorites, space-weathered surfaces and rocky planetary bodies. In particular, this investigation is expected to have a strong impact on the interpretation of reflectance measurements of Mercury. Acknowledgments: Part of this research was supported by ASI-INAF Simbio-sys agreement. E.B. and C.C. are supported also by ASI-INAF 2018-16-HH.0 (Ol-BODIES) agreement.

How to cite: Bruschini, E., Carli, C., Capaccioni, F., Vincendon, M., Buellet, A.-C., Vetere, F., Secchiari, A., Ferrari, M., Perugini, D., and Montanini, A.: The effects of graphite and particles size on reflectance spectra of silicates, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2704, https://doi.org/10.5194/egusphere-egu21-2704, 2021.

PS2.1 – Atmospheres and exospheres of terrestrial planets, satellites, and exoplanets

EGU21-8424 | vPICO presentations | PS2.1

OLYMPIA - a compact laboratory Orbitrap-based high-resolution mass spectrometer laboratory set-up: Performance studies for gas composition measurement in analogues of planetary environments

Illia Zymak, Arnaud Sanderink, Bertrand Gaubicher, Jan Žabka, Jean-Pierre Lebreton, and Christelle Briois

In situ composition measurements at Saturn and its moons (Cassini-Huygens1,2) and at comet 67P/Churyumov-Gerasimenko (Rosetta3,4) unveiled the complexity of the atmospheric chemical composition and high abundance of organic compounds in the environments of Solar System bodies. The deciphering of the measurements, obtained by current state-of-the-art instruments, to obtain the composition of complex gas mixtures that include polyatomic molecules and volatile organic compounds (VOCs) often requires having recourse to instrument response modeling supplemented by theoretical chemical models.

One of the limitations in currently flown mass spectrometers is their limited mass resolving power. High mass-resolving power offers the capability to identify unambiguously almost all complex organic compounds. Such technique offers identification of almost all complex organic compounds without application of complementary separation techniques, e.g. chromatography, spectroscopy or collision induced dissociation. A new generation of space mass spectrometers under development (MASPEX5, MULTUM6, CORALS7, CRATER7, among others), aims at reaching mass resolution of > 50 000. CORALS and CRATER are Orbitrap-based instruments using CosmOrbitrap elements.

In collaboration with J. Herovsky institute, the Laboratoire de Physique et de Chimie de l'Environnement et de l'Espace (LPC2E) has developed a new laboratory test-bench based on the Orbitrap™ technology OLYMPIA (Orbitrap anaLYseur MultiPle IonisAtion) to evaluate several space applications of an Orbitrap-based space instrument using different ionization techniques. OLYMPIA is a compact, transportable set-up and is intended to be used as a stand-alone device (currently with an EI ionization source), but later intended to be coupled to different sources of ions. The next step in the next few months is to couple it with the LLILBID set-up in Berlin8.

OLYMPIA is currently directly coupled with a first prototype of a compact electron impact ionization source. A single shot provides a useful signal duration of 200-250ms second before it decays to the noise level, and provide mass resolution for Kr ion isotopes of the order of 30 000 and on C2H4 on fragments of the order of 40 000. Kr is mostly being used to characterize the isotopic measurement capability of OLYMPIA and mixtures of C2H4, CO and N2gases in different proportions.  In this presentation we concentrate on the capability to detect low ethylene lighter VOC concentration in different mixtures of CO and N2. Sensitivity of the instrument is sufficient to detect traces of the carbon dioxide gas in mixture with molecular nitrogen abundant in less than 1% volume ratio.

1 Waite, J. H. et al. Space Sci. Rev. 114, 113–231 (2004)

2 Coates, A. J. et al. Geophys. Res. Lett. 34, (2007)

3 Balsiger, H. et al. Space Sci. Rev. 128, 745–801 (2007)

4 Le Roy, L. et al. A&A 583, (2015)

5 Brockwell, T. G. et al. in 2016 IEEE Aerospace Conference 1–17 (2016)

6 Shimma, S. et al. Anal. Chem. 82, 8456–8463 (2010)

7 Arevalo Jr, R. et al. Rapid Commun. Mass Spectrom. 32, 1875–1886 (2018)

8 Klenner, F. et al. Astrobiology 20, 179–189 (2019)

How to cite: Zymak, I., Sanderink, A., Gaubicher, B., Žabka, J., Lebreton, J.-P., and Briois, C.: OLYMPIA - a compact laboratory Orbitrap-based high-resolution mass spectrometer laboratory set-up: Performance studies for gas composition measurement in analogues of planetary environments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8424, https://doi.org/10.5194/egusphere-egu21-8424, 2021.

EGU21-10036 | vPICO presentations | PS2.1

AtmoFlow - Investigating planetary fluid flow on the International Space Station

Peter Haun, Florian Zaussinger, Peter Szabo, and Christoph Egbers

AtmoFlow is the third spherical shell experiment designed to investigate planetary flow structures under microgravity conditions. It is in fact the subsequent investigation of a series of experiments on the ISS namely GeoFlow I and GeoFlow II which investigated mantle convection with and without volumetric heating. As the name already indicated the AtmoFlow experiment is designed for the purpose to investigate atmospheric flow structures and their sensibility of changes in the thermal boundary conditions. The experiment is designed to reveal the influence of melting polar ice caps, the role of the baroclinic jet stream and thus on global climate change.

 

In general, there are three main challenges in constructing such an experiment. First, a radial force field is required which surrogates the buoyancy force under micro gravity conditions. Second, the thermal boundary conditions are non-uniform accordingly to the temperature distribution on earth’s surface, with features as cold North and South Pole as well as a hot equatorial zone. The third challenge considers the measurement technique and the restriction to the flow visualisation which has to rely on non-invasive methods, without particles.

 

A radial force field, similar to the earth gravity is established between both spherical boundaries by applying an alternating electric potential. Thus, the experiment can be considered as a spherical capacitor. Buoyancy may than be expressed via an electric force term, the dielectrophoretic force and is in fact an equivalent term to the Archimedean buoyancy for thermo-electrohydrodynamic convection. An electric Rayleigh number may than be formulated which is comparable to the well-known Rayleigh number formulated by Lord Rayleigh.

In order to fulfil the requirements of the thermal boundary conditions, the experiment is thermalised by a heating circuit for the inner sphere and a cooling circuit for each pole, respectively.

The visualization of the thermal flow between both spherical shells is achieved by a Wollaston shearing interferometry (WSI) unit. This method is able to provide high resolved information of the temperature difference between both shells. However, the system is difficult to align and adjust. Results may also be difficult to interpret as reference cases are missing. For this purpose, we are conducting complementary numerical investigations and ground experiments to fully resolve the recorded images of the AtmoFlow project.

 

In combining experimental and numerical investigations one will obtain a better understanding of the physical process in thermo-electric convection. When the experiment is sent to the ISS, we expect to observe various flow structures with temporal evolution to investigate zonal flow fields, their implication on global weather formation and climate.

How to cite: Haun, P., Zaussinger, F., Szabo, P., and Egbers, C.: AtmoFlow - Investigating planetary fluid flow on the International Space Station, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10036, https://doi.org/10.5194/egusphere-egu21-10036, 2021.

EGU21-13639 | vPICO presentations | PS2.1

Effects of ionisation on cloud behaviour in planetary atmospheres

Martin Airey, Giles Harrison, Karen Aplin, and Christian Pfrang

Cosmic rays cause ionisation in all planetary atmospheres. As they collide with particles in the atmosphere, secondary charged particles are produced that lead to the formation of cluster ions. The incident cosmic ray flux and atmospheric density of the atmosphere in question determine a profile of ion production rate. From the top of the atmosphere to the planetary surface, this rate increases with atmospheric density to a point where the flux becomes attenuated such that the rate then decreases, resulting in a peak ion production rate at some height known as the Pfotzer-Regener maximum. When these ions interact with aerosols and cloud particles, a net charge results on those particles and this is known to affect their microphysical attributes and behaviour. For example, charging may enable the activation of droplets at lower saturation ratios and also enhance collision efficiency and droplet growth. This becomes important when clouds occur at a height where ionisation is sufficient to have a substantive charging effect on the cloud particles. This has very little direct effect on Earth as peak ion production occurs high above the clouds at 15-20 km; however, on Venus for example the Pfotzer-Regener maximum occurs at ~63 km, coinciding with the main sulphuric acid cloud deck. In situations such as this, the direct result of cloud charging due to cosmic ray induced ionisation may strongly influence cloud processes, their occurrence, and behaviour.

This work uses laboratory experiments to explore the effects of charging on cloud droplets. Individual droplets are levitated in a vertical acoustic standing wave and then monitored using a CCD camera with a high magnification objective lens to determine the droplet lifetime and evaporation rate. Experiments were conducted using both the droplets’ naturally occurring charge as well as some where the region around the drop was initially flooded with ions from an external corona source. The polarity and charge magnitude of the droplets was determined by applying a 10 kV/m electric field horizontally across the drop and observing its deflection towards one of the electrodes. Theory predicts that the more highly charged a droplet is, the more resistant to evaporation it becomes. Experimental data collected during this study agrees with this, with more highly charged droplets observed to have slower evaporation rates. However, highly charged drops were also observed to periodically become unstable during evaporation and undergo Rayleigh explosions. This occurs when the droplet evaporates until its diameter becomes such that its fissility reaches the threshold at which the instability occurs. Each instability of a highly charged drop removes mass, reducing the overall droplet lifetime regardless of the slower evaporation rate. Therefore, where enhanced ionisation occurs in the presence of clouds the end result may be to reduce droplet stability.

How to cite: Airey, M., Harrison, G., Aplin, K., and Pfrang, C.: Effects of ionisation on cloud behaviour in planetary atmospheres, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13639, https://doi.org/10.5194/egusphere-egu21-13639, 2021.

EGU21-9457 | vPICO presentations | PS2.1

Global 3D modelling of Martian CO2 clouds

Christophe Mathé, Anni Määttänen, Joachim Audouard, Constantino Listowski, Ehouarn Millour, François Forget, Aymeric Spiga, Déborah Bardet, Lucas Teinturier, Lola Falletti, Margaux Vals, Franscico González-Galindo, and Franck Montmessin

In the Martian atmosphere, carbon dioxide (CO2) clouds have been revealed by numerous instruments around Mars from the beginning of the XXI century. These observed clouds can be distinguished by two kinds involving different formation processes: those formed during the winter in polar regions located in the troposphere, and those formed during the Martian year at low- and mid-northern latitudes located in the mesosphere (Määattänen et al, 2013). Microphysical processes of the formation of these clouds are still not fully understood. However, modeling studies revealed processes necessary for their formation: the requirement of waves that perturb the atmosphere leading to a temperature below the condensation of CO2 (transient planetary waves for tropospheric clouds (Kuroda et al., 20123), thermal tides (Gonzalez-Galindo et al., 2011) and gravity waves for mesospheric clouds (Spiga et al., 2012)). In the last decade, a state-of-the-art microphysical column (1D) model for CO2 clouds in a Martian atmosphere was developed at Laboratoire Atmosphères, Observations Spatiales (LATMOS) (Listowski et al., 2013, 2014). We use our full microphysical model of CO2 cloud formation to investigate the occurrence of these CO2 clouds by coupling it with the Global Climate Model (GCM) of the Laboratoire de Météorologie Dynamique (LMD) (Forget et al., 1999). We recently activated the radiative impact of CO2 clouds in the atmosphere. Last modeling results on Martian CO2 clouds properties and their impacts on the atmosphere will be presented and be compared to observational data.

How to cite: Mathé, C., Määttänen, A., Audouard, J., Listowski, C., Millour, E., Forget, F., Spiga, A., Bardet, D., Teinturier, L., Falletti, L., Vals, M., González-Galindo, F., and Montmessin, F.: Global 3D modelling of Martian CO2 clouds, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9457, https://doi.org/10.5194/egusphere-egu21-9457, 2021.

EGU21-7617 | vPICO presentations | PS2.1

Drivers of Mars' northern winter polar vortex

Emily Ball, Dann Mitchell, William Seviour, Geoffrey Vallis, and Stephen Thomson

Mars’ polar vortices play a mjaor role in determining the global-scale transport of trace gases and the composition of the polar caps. Potential vorticity (PV) is a key quantity in determining their dynamical and transport properties. Mars' winter polar vortices are annular in PV, a direct contrast to Earth’s stratospheric polar vortices, whose PV values increase monotonically towards the poles. Given that a ring of high PV is known to be barotropically unstable, the persistence of this phenomenon in observations, simulations and reanalyses is somewhat surprising. Condensation of atmospheric carbon dioxide at the winter pole has been shown to be necessary to maintain the annulus in Martian Global Circulation Models (MGCM). Dust is also known to be a cause of internal and interannual variability in the polar vortices, but given the relatively few years of observations available, it is not yet fully understood. Here we present results of an attribution study of the driving mechanisms of the northern hemisphere Martian polar vortex. Using a reanalysis dataset and an idealized MGCM, we investigate the combined effects of dust, latent heat release, and topography on the polar vortex.

We show that the vertical PV structure of the polar vortex in the reanalysis is dependent on the observations assimilated, and that high atmospheric dust loading (such as that seen during a global dust storm) can disrupt the vortex and cause the destruction of PV in the low-mid altitudes. We also demonstrate that high dust loading can significantly reduce eddy activity within the core of the vortex over the course of a Martian winter. Latent heat release from carbon dioxide condensation is an important driver of variability within the polar vortex, but it is dust in the model that primarily drives the eddy activity throughout the Martian year.

How to cite: Ball, E., Mitchell, D., Seviour, W., Vallis, G., and Thomson, S.: Drivers of Mars' northern winter polar vortex, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7617, https://doi.org/10.5194/egusphere-egu21-7617, 2021.

EGU21-7918 | vPICO presentations | PS2.1

Exploring de formation of the Arsia Mons Elongated Cloud on Mars

Jorge Hernandez-Bernal, Agustín Sánchez-Lavega, and Teresa Del Río-Gaztelurrutia

In a recent work (Hernández-Bernal et al. 2020) we reported the existence and properties of the AMEC (Arsia Mons Elongated Cloud). This cloud appears every martian year around the southern solstice following a quick daily cycle, it expands up to 1800 km after sunrise and disappears before noon. While in the previous work we made an extensive observational study, a number of questions remain unsolved, including the specific specific set of atmospheric conditions that originates this particular cloud at this moment of the year, and why other near volcanoes do not exhibit analogous clouds. In this work we explore, based on models, the physical conditions of the atmosphere around Arsia Mons, such as temperature gradients, winds, and water vapor distribution, as a first step to try to understand this particular cloud.

References:

Hernández-Bernal, J., Sánchez-Lavega, A., Río-Gaztelurrutia, T. D., Ravanis, E., Cardesín-Moinelo, A., Connour, K., ... & Hauber, E. An Extremely Elongated Cloud over Arsia Mons Volcano on Mars: I. Life Cycle. Journal of Geophysical Research: Planets, DOI: 10.1029/2020JE006517

How to cite: Hernandez-Bernal, J., Sánchez-Lavega, A., and Del Río-Gaztelurrutia, T.: Exploring de formation of the Arsia Mons Elongated Cloud on Mars, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7918, https://doi.org/10.5194/egusphere-egu21-7918, 2021.

EGU21-14926 | vPICO presentations | PS2.1

Enhanced water loss during the Mars Year 34 C storm

James Holmes, Stephen Lewis, Manish Patel, Michael Chaffin, Eryn Cangi, Justin Deighan, Nicholas Schneider, Shohei Aoki, Anna Fedorova, David Kass, and Ann Carine Vandaele

We investigate the evolving water vapour and hydrogen distribution in the martian atmosphere and their associated effect on hydrogen escape during the Mars Year (MY) 34 C storm (a late winter regional dust storm that occurs every Mars year). Improved calculation of the integrated loss of water throughout Mars‘ history (that is currently not well constrained) is possible through tracking the water loss through time from global simulations constrained by available observations. Through constraining water loss we can provide better insight into planetary evolution.

The Open University modelling group global circulation model is combined with retrievals from the ExoMars Trace Gas Orbiter (temperature and water vapour profiles from the Atmospheric Chemistry Suite and water vapour profiles from the Nadir and Occultation for Mars Discovery instrument) and the Mars Climate Sounder (temperature profiles and dust column) on the Mars Reconnaissance Orbiter. This multi-spacecraft assimilation provides the best possible replication of the evolving lower atmosphere.

The unusually intense dusty conditions during the MY 34 C storm led to increased amounts of water vapour and hydrogen above 80 km compared to a more typical C storm, which had an important impact on the amount of water escaping Mars’ atmosphere. Modelled hydrogen escape rates during the MY 34 C storm peaked at around 1.4 x 109 cm-2 s-1, three times the escape rate calculated in the MY 30 C storm scenario and equivalent to those found during previous global-scale dust storms. The weak MY 30 C storm and strong MY 34 C storm can be seen as a bracketing pair of events and therefore the calculated escape rates represent the interannual variabiity expected during C storm events.

Our results indicate water loss during the C storm event each year is highly variable, and must be considered when calculating the integrated loss of water through Mars’ history.

How to cite: Holmes, J., Lewis, S., Patel, M., Chaffin, M., Cangi, E., Deighan, J., Schneider, N., Aoki, S., Fedorova, A., Kass, D., and Vandaele, A. C.: Enhanced water loss during the Mars Year 34 C storm, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14926, https://doi.org/10.5194/egusphere-egu21-14926, 2021.

EGU21-12721 | vPICO presentations | PS2.1

Observations of CO2 clouds on Mars from TIRVIM and NIR solar occultation measurements onboard TGO

Mikhail Luginin, Nikolay Ignatiev, Anna Fedorova, Alexander Trokhimovskiy, Alexey Grigoriev, Alexey Shakun, Franck Montmessin, and Oleg Korablev

Carbon dioxide is the major constituent of the Martian atmosphere. Its seasonal cycle plays an important role in atmospheric dynamics and climate. Formation of the polar CO2 frost deposits results in up to 30% of atmospheric pressure variations as well as in dramatic change in surface reflectance and emissivity. Another case of carbon dioxide condensation is formation of a CO2 clouds that are still poorly studied, despite the fact that they have been observed by a number of instruments [1−6] on the orbit of Mars.

In this work, we will present first results of CO2 clouds observations from a combination of thermal-infrared (1.7−17 µm) and near-infrared (0.7-1.6 µm) spectra measured by TIRVIM and NIR instruments onboard the ExoMars Trace Gas Orbiter (TGO) in solar occultation geometry. These instruments are part of the Atmospheric Chemistry Suite (ACS), a set of three spectrometers (NIR, MIR, and TIRVIM) that is conducting scientific measurements on the orbit of Mars since the spring of 2018 [7].

This work was funded by Russian Science Foundation, grant number 20-42-09035.

References

[1] Montmessin et al. (2006). Subvisible CO2 ice clouds detected in the mesosphere of Mars. Icarus, 183, 403–410. https://doi.org/10.1016/j.icarus.2006.03.015

[2] Montmessin et al. (2007). Hyperspectral imaging of convective CO2 ice clouds in the equatorial mesosphere of Mars. Journal of Geophysical Research, 112, E11S90. https://doi.org/10.1029/2007JE002944

[3] Määttänen et al. (2010). Mapping the mesospheric CO2 clouds on Mars: MEx/OMEGA and MEx/HRSC observations and challenges for atmospheric models. Icarus, 209, 452–469. https://doi.org/10.1016/j.icarus.2010.05.017

[4] McConnochie et al. (2010). THEMIS-VIS observations of clouds in the Martian mesosphere: Altitudes, wind speeds, and decameter-scale morphology. Icarus, 210, 545–565. https://doi.org/10.1016/j.icarus.2010.07.021

[5] Vincendon et al. (2011). New near-IR observations of mesospheric CO2 and H2O clouds on Mars. Journal of Geophysical Research, 116, E00J02. https://doi.org/10.1029/2011JE003827

[6] Jiang et al., (2019). Detection of Mesospheric CO 2 Ice Clouds on Mars in Southern Summer. Geophysical Research Letters, 46(14), 7962–7971. https://doi.org/10.1029/2019GL082029

[7] Korablev et al., (2018). The Atmospheric Chemistry Suite (ACS) of three spectrometers for the ExoMars 2016 Trace Gas Orbiter. Space Sci. Rev. 214, 7. doi:10.1007/s11214-017-0437-6

How to cite: Luginin, M., Ignatiev, N., Fedorova, A., Trokhimovskiy, A., Grigoriev, A., Shakun, A., Montmessin, F., and Korablev, O.: Observations of CO2 clouds on Mars from TIRVIM and NIR solar occultation measurements onboard TGO, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12721, https://doi.org/10.5194/egusphere-egu21-12721, 2021.

EGU21-10804 | vPICO presentations | PS2.1

Sluggish hydrodynamic escape of early Martian atmosphere with reduced chemical compositions

Tatsuya Yoshida and Kiyoshi Kuramoto

   Mars may have obtained a proto-atmosphere enriched in H2, CH4, and CO during accretion. Such a reduced proto-atmosphere would have been largely lost by hydrodynamic escape, but its flux is highly uncertain. To estimate the evolution of the proto-atmosphere of Mars correctly, an exact escape modeling including exact radiative balance and chemical processes is required partly because those reduced species and their photochemical products may act as an effective coolant that suppresses the escape of atmosphere. Here we develop a one-dimensional hydrodynamic escape model that includes radiative processes and photochemical processes for a multi-component atmosphere and apply to the reduced proto-atmosphere on Mars.

   Under the enhanced XUV flux suggested for young Sun, the escape flux decreases by more than one order of magnitude with increasing the mixing fraction of CH4 and CO  from zero to > 10 % mainly because of the energy loss by radiative cooling by these infrared active chemical molecules. Concurrently, the mass fractionation between H2 and other heavier species becomes to be enhanced. Given that the proto-Mars initially obtained > 10 bar of H2 and carbon species equivalent to 1 bar of CO2 was then left behind after the end of the hydrodynamic escape of H2, the total amount of carbon species lost by hydrodynamic escape is estimated to be equivalent to 20 bar of CO2 or more. Such a severe loss of carbon species may explain the paucity of CO2 on Mars compared to Earth and Venus. If the proto-Mars obtained > 100 bar of H2, the timescale for H2 escape exceeds ~100 Myr. This implies that an atmosphere with reduced chemical compositions allowing the production of organic matter deposits may have been kept on early Mars traceable by geologic records.

How to cite: Yoshida, T. and Kuramoto, K.: Sluggish hydrodynamic escape of early Martian atmosphere with reduced chemical compositions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10804, https://doi.org/10.5194/egusphere-egu21-10804, 2021.

EGU21-12816 | vPICO presentations | PS2.1

Analysis of radio occultation data to determine atmospheric profiles and associated uncertainties 

Flavio Petricca, Gael Cascioli, and Antonio Genova

The analysis of atmospheric radio occultations enables an in-depth investigation of planetary ionosphere and neutral atmospheres, by measuring the radio frequency shift that affects a signal propagating through the medium. A precise characterization of the atmospheric layers requires a thorough processing of the radio tracking data to estimate the thermodynamic properties of the atmosphere and their related uncertainties.

A standard procedure to process radio occultation data requires a preliminary knowledge of the spacecraft trajectory. In this work, we present a technique to retrieve refractivity, density, pressure, and temperature profiles with their associated uncertainties through the analysis of raw radio tracking data occulted by the atmosphere. By integrating the algorithm for radio occultation processing with a Precise Orbit Determination (POD) software, an enhanced reconstruction of the spacecraft trajectory is obtained to recover the frequency shift due to the medium refraction. The resulting radio signal is then processed to yield information regarding atmospheric properties. A Monte Carlo simulation algorithm is also included to provide the formal uncertainties of the estimated parameters.

We applied this technique to radio occultation profiles of the NASA mission Mars Reconnaissance Orbiter (MRO). To validate the method, our estimated atmospheric profiles are compared to the numerical predictions of the Mars Global Reference Atmospheric Model (GRAM) and the Mars Climate Database (MCD).

How to cite: Petricca, F., Cascioli, G., and Genova, A.: Analysis of radio occultation data to determine atmospheric profiles and associated uncertainties , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12816, https://doi.org/10.5194/egusphere-egu21-12816, 2021.

EGU21-5562 | vPICO presentations | PS2.1

Impact of atmospheric gravity waves on the Martian global water cycle during dust storms

Dmitry Shaposhnikov, Alexander Medvedev, Alexander Rodin, and Paul Hartogh

Effects of atmospheric gravity waves (GWs) on the global water cycle in the middle and high atmosphere of Mars during the global dust storms (Martian years 28 and 34) have been studied for the first time using a general circulation model. Dust storm simulations were compared with those utilizing the climatological distribution of dust in the absence of a GW parameterization. The dust storm scenarios are based on the observations of the dust optical depth by the Mars Climate Sounder instrument on board Mars Reconnaissance Orbiter. The simulations show that accounting for the influence of GWs leads to a change in the concentration of water vapor in the thermosphere. The most significant effect of GWs is twofold. First, cooling of the thermosphere at the poles leads to a decrease in the water vapor abundance during certain periods. Second, heating in the regions representing the main channels of water supply to the upper atmosphere (the so-called water "pump" mechanism) increases, on the contrary, its concentration. Since the temperature increase provides more intensive atmospheric mixing, and also expands the supply channel through an increase in saturation pressure. The dynamic balance of these basic mechanisms drives the changes in the distribution of water vapor in the upper atmosphere. Dust storms enhance pumping of water vapor into the upper atmosphere. Seasonal differences in the storm occurrences in different years allow for tracking the paths of water vapor transport to the upper atmosphere.

How to cite: Shaposhnikov, D., Medvedev, A., Rodin, A., and Hartogh, P.: Impact of atmospheric gravity waves on the Martian global water cycle during dust storms, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5562, https://doi.org/10.5194/egusphere-egu21-5562, 2021.

EGU21-5515 | vPICO presentations | PS2.1

The Venus Climate Database

Sebastien Lebonnois, Ehouarn Millour, Antoine Martinez, Thomas Pierron, Aymeric Spiga, Jean-Yves Chaufray, Franck Montmessin, and Fabrice Cipriani

We have over the years developed a state of the art Venus Global Climate Model (GCM, Lebonnois et al. 2016; Gilli et al. 2017; Garate-Lopez & Lebonnois 2018). With funding from ESA in the context of the preparation of the possible upcoming EnVision mission, we have, in the footsteps of what has been done for Mars with the Mars Climate Database (), built a Venus Climate Database (VCD) based on GCM outputs.

The VCD dataset and software overall enable users to:

- extract atmospheric quantities (temperature, pressure, winds, density, …) from the surface to the exobase (~250km) over a climatological Venusian day.

- to better bracket reality, several scenarios are provided, in order to reflect the possible range of solar activity (Extreme UV input from the Sun) which strongly affects the thermosphere (above ~150km), as well as a realistic range of UV albedo cloud top.

- in addition to a baseline climatology, the VCD software provides statistics (internal short term and day-to-day variability) along with means to add perturbations to represent Venusian weather.

At EGU we will present the VCD and its features, emphasizing how it can be useful for scientific users wanting to compare with their models or analyze observations, and for engineers planning future missions.

How to cite: Lebonnois, S., Millour, E., Martinez, A., Pierron, T., Spiga, A., Chaufray, J.-Y., Montmessin, F., and Cipriani, F.: The Venus Climate Database, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5515, https://doi.org/10.5194/egusphere-egu21-5515, 2021.

EGU21-5025 | vPICO presentations | PS2.1

Comparison between IPSL Venus Global Climate Model results and aerobraking data

Antoine Martinez, Sébastien Lebonnois, Jean-Yves Chaufray, Ehouarn Millour, and Thomas Pierron

For fifteen years, a Global Climate Model (GCM) has been developed for the Venus atmosphere at Institut Pierre-Simon Laplace (IPSL), in collaboration between LMD and LATMOS, from the surface up to 150 km altitude. Its recent extension up to the exobase (roughly 250 km) within the framework of the VCD project now allows us to simulate the Venusian upper atmosphere and the key atmospheric parameters of the aerobraking phases. The aim of this presentation is to study the evolution of the density of the Venusian upper atmosphere as a function of different parameters such as solar irradiance, latitude, local time and zenith solar angle (SZA), for regions from 130 to 180 km of altitude. We will present here several comparisons of the upper atmosphere of Venus between our model results and a selection of aerobraking data from different missions such as Venus Express, Pioneer Venus and Magellan.

How to cite: Martinez, A., Lebonnois, S., Chaufray, J.-Y., Millour, E., and Pierron, T.: Comparison between IPSL Venus Global Climate Model results and aerobraking data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5025, https://doi.org/10.5194/egusphere-egu21-5025, 2021.

EGU21-3657 | vPICO presentations | PS2.1

Atmospheric general circulation and waves simulated by a Venus AORI GCM with topographical and radiative forcings

Masaru Yamamoto, Takumi Hirose, Kohei Ikeda, and Masaaki Takahashi

General circulation and waves are investigated using a T63 Venus general circulation model (GCM) with solar and thermal radiative transfer in the presence of high-resolution surface topography. This model has been developed by Ikeda (2011) at the Atmosphere and Ocean Research Institute (AORI), the University of Tokyo, and was used in Yamamoto et al. (2019, 2021). In the wind and static stability structures similar to the observed ones, the waves are investigated. Around the cloud-heating maximum (~65 km), the simulated thermal tides accelerate an equatorial superrotational flow with a speed of ~90 m/swith rates of 0.2–0.5 m/s/(Earth day) via both horizontal and vertical momentum fluxes at low latitudes. Over the high mountains at low latitudes, the vertical wind variance at the cloud top is produced by topographically-fixed, short-period eddies, indicating penetrative plumes and gravity waves. In the solar-fixed coordinate system, the variances (i.e., the activity of waves other than thermal tides) of flow are relatively higher on the night-side than on the dayside at the cloud top. The local-time variation of the vertical eddy momentum flux is produced by both thermal tides and solar-related, small-scale gravity waves. Around the cloud bottom, the 9-day super-rotation of the zonal mean flow has a weak equatorial maximum and the 7.5-day Kelvin-like wave has an equatorial jet-like wind of 60-70 m/s. Because we discussed the thermal tide and topographically stationary wave in Yamamoto et al. (2021), we focus on the short-period eddies in the presentation.

How to cite: Yamamoto, M., Hirose, T., Ikeda, K., and Takahashi, M.: Atmospheric general circulation and waves simulated by a Venus AORI GCM with topographical and radiative forcings, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3657, https://doi.org/10.5194/egusphere-egu21-3657, 2021.

EGU21-5999 | vPICO presentations | PS2.1

Venus, an Astrobiology Target

Sanjay Limaye, Rakesh Mogul, Kevin Baines, Mark Bullock, Charles Cockell, James Cutts, Diana Gentry, James Head, Kandis-Lea Jessup, Vladimir Kompanichenko, Yeon Joo Lee, Richard Mathies, Tetyana Milojevic, Rosalyn Pertzborn, Lynn Rothschild, Dirk Schulze-Makuch, David Smith, and Michael Way

The interest in the possibility of life on Venus is driven not just by curiosity about life originating in another Earth-like environment, but because of the possibility that life may be playing a critical role in the planet’s present, and possibly its past, atmospheric state. The brilliance of Venus in the night sky (as viewed from Earth) is due to its highly reflective cloud cover, about 28 km thick at the equator.  Its spectral albedo is about 90% at wavelengths > 500 nm, but it drops gradually to about 40% around 370 nm before rising slightly at shorter wavelengths.  This albedo drop is due to the presence of several absorbers in the atmosphere and the cloud cover.  A very large fraction of the energy absorbed by Venus is at ultraviolet wavelengths with sulfur dioxide above the clouds contributing to the absorption below 330 nm; however, the identities of the other absorbers remain unknown.  The inability to identify the absorbers that are responsible for determining the radiative energy balance of Venus over the last century is a major impediment to understanding how the planet “works”, a major component of NASA’s efforts in planetary exploration.  Limaye et al. (Astrobiology 18, 1181-1198, 2018) presented a hypothesis suggesting that cloud-based microbial life could be contributors to the spectral signatures of Venus’ clouds, building upon previous suggestions of the possibility of life in the clouds of Venus.

Four interconnected themes for the exploration of Venus as an astrobiology target are: – (i) investigations focused on the likelihood that liquid water existed on the surface in the past leading to the potential for the origin and evolution of life, (ii) investigations into the potential for habitable zones within Venus’ clouds and Venus-like atmospheres, (iii) theoretical investigations into how active aerobiology may impact the radiative energy balance of Venus’ clouds and Venus-like atmospheres, and (iv) application of these investigative themes towards better understanding the atmospheric dynamics and habitability of exoplanets. These themes can serve as a basis for proposed Venus Astrobiology Objectives and suggestions for measurements for future missions, as per the goals and objectives developed by the Venus Exploration Analysis Group (VEXAG), which is sponsored by NASA to plan for the future exploration of Venus.  

A Venus Collection to be published in Astrobiology journal in 2021 will include papers from the  “Habitability of the Venus Cloud Layer”, Moscow (October 2019) workshop. 

How to cite: Limaye, S., Mogul, R., Baines, K., Bullock, M., Cockell, C., Cutts, J., Gentry, D., Head, J., Jessup, K.-L., Kompanichenko, V., Lee, Y. J., Mathies, R., Milojevic, T., Pertzborn, R., Rothschild, L., Schulze-Makuch, D., Smith, D., and Way, M.: Venus, an Astrobiology Target, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5999, https://doi.org/10.5194/egusphere-egu21-5999, 2021.

EGU21-7453 | vPICO presentations | PS2.1

Planetary aerosol electrification: Lessons learned from a terrestrial analogy for Venus

Amethyst Johnson and Karen Aplin

Planetary atmospheric electrification has the potential to damage spacecraft, yet for planets with thick, deep atmospheres such as Venus, the level of electrification remains open to interpretation. Partly due to the difficulty of access and potential hostility to spacecraft, there are limited in-situ observations of deep atmospheres, making terrestrial analogies attractive. One proposed explanation of the observations of near-surface electrification on Venus from sensors on Venera 13 & 14 is a haze of charged aerosol. As the Sahara is an environment with lofted dust that is potentially similar to Venus in terms of atmospheric stability, a simple model was developed estimating a mean aerosol charge based on typical Saharan haze aerosol distributions. Spacecraft surface area and descent speeds were used to estimate the accumulated charge and discharge current measured by the Venera missions, but this model underestimated Venera's electrical measurements by three orders of magnitude. This suggests that an aerosol layer alone cannot explain the charge apparently present in the lower atmosphere of Venus. The simple terrestrial analogy employed may not have been suitable due to the modified pressure and temperature profile affecting the mean free path, ionic mobility and consequently the mean charge. Discrepancies in atmospheric stability and wind patterns must also be evaluated, as the effect of terrestrial wind on aerosol distributions may not be directly applicable to other planets. More detailed calculations of ion-aerosol attachment and re-evaluation of the terrestrial analogy may be able to resolve some these issues, but it looks likely that additional significant sources of charge are required to explain the Venera observations. Triboelectric charging of lofted surface material could exceed charging observed in terrestrial situations, or some unknown atmospheric or non-atmospheric source of charge could have contributed to the Venera electrical measurements. 

How to cite: Johnson, A. and Aplin, K.: Planetary aerosol electrification: Lessons learned from a terrestrial analogy for Venus, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7453, https://doi.org/10.5194/egusphere-egu21-7453, 2021.

EGU21-14528 | vPICO presentations | PS2.1

Short-term modulations of Venus’ disk-integrated brightness observed from the Venus orbiter Akatsuki

Yeon Joo Lee, Antonio García Muñoz, Takeshi Imamura, Manabu Yamada, Takehiko Satoh, Atsushi Yamazaki, and Shigeto Watanabe

We show that Venus’ disk-integrated brightness at 283, 365, and 2020 nm is modulated by one or both of two periods of 3.7 and 4.6 days, as observed from the Akatsuki Venus orbiter of JAXA. Their typical amplitudes are <10%, but there are occasional events of 20–40%. We find a clear anti-correlation between UV and 2020-nm signals, implying that the cloud top altitudes (2020 nm) and the abundances of UV absorbers (283 and 365 nm) change simultaneously in the global scale. We note that the detected modulations, and their wavelength dependent signals imply the existence of an atmosphere if detected at an exoplanet. Our results should be useful in future direct imaging of terrestrial exoplanets. More details are shown in our paper (https://doi.org/10.1038/s41467-020-19385-6).

How to cite: Lee, Y. J., García Muñoz, A., Imamura, T., Yamada, M., Satoh, T., Yamazaki, A., and Watanabe, S.: Short-term modulations of Venus’ disk-integrated brightness observed from the Venus orbiter Akatsuki, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14528, https://doi.org/10.5194/egusphere-egu21-14528, 2021.

EGU21-778 | vPICO presentations | PS2.1

Modelling of Io’s Atmosphere for the IVO Mission

Peter Wurz, Audrey Vorburger, Alfred McEwen, Kathy Mandt, Ashley Davies, Sarah Hörst, and Nicolas Thomas

The Io Volcano Observer (IVO) is a proposed NASA Discovery-class mission (currently in Phase A), that would launch in early 2029, arrive at  Jupiter in the early 2033, and perform ten flybys of Io while in Jupiter's orbit. IVO's mission motto is to 'follow the heat', shedding light onto tidal heating as a fundamental planetary process. Specifically, IVO will determine (i) how and where heat is generated in Io's interior, (ii) how heat is transported to the surface, and (iii) how Io has evolved with time. The answers to these questions will fill fundamental gaps in the current understanding of the evolution and habitability of many worlds across our Solar System and beyond where tidal heating plays a key role, and will give us insight into how early Earth, Moon, and Mars may have worked.

One of the five key science questions IVO will be addressing is determining Io's mass loss via atmospheric escape. Understanding Io's mass loss today will offer information on how the chemistry of Io has been altered from its initial state and would provide useful clues on how atmospheres on other bodies have evolved over time. IVO plans on measuring Io's mass loss in situ with the Ion and Neutral Mass Spectrometer (INMS), a successor to the instrument currently being built for the JUpiter Icy moons Explorer (JUICE). INMS will measure neutrals and ions in the mass range 1 – 300 u, with a mass resolution (M/ΔM) of 500, a dynamic range of > 105, a detection threshold of 100 cm–3 for an integration time of 5 s, and a cadence of 0.5 – 300 s per spectrum.

In preparation for IVO, we model atmospheric density profiles of species known and expected to be present on Io's surface from both measurements and previous modelling efforts. Based on the IVO mission design, we present three different measurement scenarios for INMS we expect to encounter at Io based on the planned flybys: (i) a purely sublimated atmosphere, (ii) the 'hot' atmosphere generated by lava fields, and (iii) the plume gases resulting from volcanic activity. We calculate the expected mass spectra to be recorded by INMS during these flybys for these atmospheric scenarios.

How to cite: Wurz, P., Vorburger, A., McEwen, A., Mandt, K., Davies, A., Hörst, S., and Thomas, N.: Modelling of Io’s Atmosphere for the IVO Mission, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-778, https://doi.org/10.5194/egusphere-egu21-778, 2021.

EGU21-2942 | vPICO presentations | PS2.1

3D Monte-Carlo Model of Europa's Water Plumes

Audrey Vorburger and Peter Wurz

With the pending launches of JUICE and Europa Clipper within the next three years, interest in Europa plumes and the implications they might hold has regained momentum.

In 2014, Roth et al. presented first evidence for Europa plume activity based on Hubble Space Telescope (HST) Space Telescope Imaging Spectograph (STIS) Lyman-alpha and OI 1304 Å line emission observations. The observed line emissions imply two underlying plumic sources, located ~20° apart, exhibiting radial expansions of ~200 km and latitudinal expansions of ~20°, and containing ~2,000 kg of H2O (~1.5 ∙ 1016 H2O/cm2). Since then, several more Europa plume observation attempts were undertaken, though only a hand full proved successful. 

Most importantly, the true nature of the observed plume signature still remains to be determined. Plumes can either originate from the topmost surface layer, from within the ice layer, or from the sub-surface ocean. Depending on the location of origin, the plumes contain information about vastly different zones: If they are surficial, they will contain information about the highly irradiated and highly processed surface, if they originate from the sub-surface ocean, they might hold information on Europa’s potentially life-bearing region.

In this presentation, we present 3D Monte-Carlo model results of three different plume scenarios, two of which originate in Europa’s surface ice layer (near-surface liquid inclusion and diapir) whereas the third originates in the sub-surface ocean (oceanic plume). In this model we trace not only the H2O molecules, but also its dissociation products, i.e., OH, H and O. To compare the plume structures obtained from the Monte-Carlo model to the HST-STIS observations, we include all known relevant Lyman-alpha and OI 1304 Å emission excitation mechanisms in our model. Such a comparison does not only shed more light on the plumes that have already been observed, but will also help targeting plume measurements in the near future, as well as interpreting in situ measurements once such become available.

How to cite: Vorburger, A. and Wurz, P.: 3D Monte-Carlo Model of Europa's Water Plumes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2942, https://doi.org/10.5194/egusphere-egu21-2942, 2021.

EGU21-10235 | vPICO presentations | PS2.1

Modelling Mineral Snowflakes in the Atmospheres of Gas-Giant Exoplanets

Dominic Samra, Christiane Helling, Michiel Min, and Til Birnstiel

Exoplanets provide excellent laboratories to explore novel atmospheric regimes; using observations coupled with microphysical models we can probe our understanding of the formation and evolution of planets beyond those in the Solar System. However, clouds remain a key challenge in observation of exoplanet atmospheres, both altering the local atmospheric composition and obscuring deeper atmospheric layers. Currently, most observed exoplanet atmospheres are tidally locked gas-giants in close orbit around their host star. These hot and ultra-hot Jupiters have day-side temperatures in excess of 2500 K, and still above 400 K on the night-side, thus they form solid clouds made of minerals, metal oxides and metals. These clouds may form snowflake like structures, either through condensation or by constructive collisions (coagulation).

We explore the effects of non-compact, non-spherical cloud particles in gas-giant exoplanet atmospheres by expanding our kinetic non-equilibrium cloud formation model, to include parameterised porous cloud particles as well as cloud particle growth and fragmentation through collisions. We apply this model to prescribed 1D temperature - pressure Drift-Phoenix atmospheric profiles, using Mie theory and effective medium theory to study cloud optical depths, representing the effects of the non-spherical cloud particles through a statistical distribution of hollow spheres.

Finally, we apply our cloud formation model to a sample of gas-giants as well as ultra-hot Jupiters, using 1D profiles extracted from the 3D SPARC/MITgcm general circulation model. In particular, we take the example cases of gas-giant WASP-43b and the ultra-hot Jupiter HAT-P-7b, where we find dramatic differences in the day-/night-side distribution of clouds between these types of exoplanets due to the intensity of stellar irradiation for HAT-P-7b. Further an asymmetry in cloud coverage at the terminators of ultra-hot Jupiters is observable in the optical depth of the clouds, which affects the observable atmospheric column and thus has implication for detection of key gas phase species. Clouds also enhance the gas phase C/O which is often used as an indicator of formation history. With next-generation instruments such as the James Webb Space Telescope (JWST) such details will begin to be examined, but we find that a detailed understanding of cloud formation processes will be required to interpret observations.

How to cite: Samra, D., Helling, C., Min, M., and Birnstiel, T.: Modelling Mineral Snowflakes in the Atmospheres of Gas-Giant Exoplanets, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10235, https://doi.org/10.5194/egusphere-egu21-10235, 2021.

EGU21-936 | vPICO presentations | PS2.1

Modelling the influence of high-energy radiation on the atmospheric composition of the hot Jupiter HD 189733b

Patrick Barth, Christiane Helling, Eva E. Stüeken, Vincent Bourrier, Nathan Mayne, Paul B. Rimmer, Moira Jardine, Aline A. Vidotto, Peter J. Wheatley, and Rim Fares

Hot Jupiters provide valuable natural laboratories for studying potential contributions of high-energy radiation to prebiotic synthesis in the atmospheres of exoplanets. HD 189733b, a hot Jupiter orbiting a K star, is one of the most studied and best observed exoplanets. We combine XUV observations and 3D climate simulations to model the atmospheric composition and kinetic chemistry with the STAND2019 network. We show how XUV radiation, cosmic rays (CR), and stellar energetic particles (SEP) influence the chemistry of the atmosphere. We explore the effect that the change in the XUV radiation has over time, and we identify key atmospheric signatures of an XUV, CR, and SEP influx. 3D simulations of HD 189733b's atmosphere with the 3D Met Office Unified Model provide a fine grid of pressure-temperature profiles, consistently taking into account kinetic cloud formation. We apply HST and XMM-Newton/Swift observations obtained by the MOVES programmewhich provide combined X-ray and ultraviolet (XUV) spectra of the host star HD 189733 at 4 different points in time. We find that the differences in the radiation field between the irradiated dayside and the shadowed nightside lead to stronger changes in the chemical abundances than the variability of the host star's XUV emission. We identify ammonium (NH4+) and oxonium (H3O+) as fingerprint ions for the ionization of the atmosphere by both galactic cosmic rays and stellar particles. All considered types of high-energy radiation have an enhancing effect on the abundance of key organic molecules such as hydrogen cyanide (HCN), formaldehyde (CH2O), and ethylene (C2H4). The latter two are intermediates in the production pathway of the amino acid glycine (C2H5NO2) and abundant enough to be potentially detectable by JWST. Ultimately, we show that high energy processes potentially play an important role in prebiotic chemistry.

P Barth et al., MOVES IV. Modelling the influence of stellar XUV-flux, cosmic rays, and stellar energetic particles on the atmospheric composition of the hot Jupiter HD 189733b, Monthly Notices of the Royal Astronomical Society, in press, DOI:10.1093/mnras/staa3989

How to cite: Barth, P., Helling, C., Stüeken, E. E., Bourrier, V., Mayne, N., Rimmer, P. B., Jardine, M., Vidotto, A. A., Wheatley, P. J., and Fares, R.: Modelling the influence of high-energy radiation on the atmospheric composition of the hot Jupiter HD 189733b, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-936, https://doi.org/10.5194/egusphere-egu21-936, 2021.

EGU21-2638 | vPICO presentations | PS2.1

How does the background atmosphere affect the onset of the runaway greenhouse? Insights from 1D radiative-convective modeling.

Guillaume Chaverot, Emeline Bolmont, Martin Turbet, and Jérémy Leconte

There is a strong interest to study the runaway greenhouse effect [1-4] to better determine the runaway greenhouse insolation threshold and therefore the inner edge of the habitable zone (HZ). Some studies [5-7] have shown that the onset of the runaway greenhouse may be delayed due to an increase of the Outgoing Longwave Radiation (OLR) by adding radiatively inactive gas (e.g. N2 or O2, as in the Earth's atmosphere). For such atmosphere the OLR may “overshoot” the Simpson-Nakajima limit [4], i.e. the moist greenhouse limit of a pure vapor atmopshere. This has direct consequences on the position of the inner edge of the HZ [8-11] and thus on how close the Earth is from a catastrophic runaway greenhouse feedback. The OLR overshoot has previously been interpreted as a modification of the atmospheric profile due to the background gas [7,12]. However there is still no consensus so far in the literature on whether an OLR overshoot is really expected or not.

The first aim of our work is to determine, through sensitivity tests, the main important physical processes and parametrizations involved in the OLR computation with a suite of 1D radiative-convective models. By doing multiple sensitivity experiments we are able to explain the origin of the differences in the results of the literature for a H2O+N2 atmosphere. We showed that physical processes usually assumed as second order effects are actually key to explain the shape of the OLR (e.g., line shape parameters). This work can also be useful to guide future 3D GCM simulations. We propose also preliminary results from the LMD-Generic model to study how these effects may be understand in a 3D simulation.

Secondly we propose a reference OLR curve, done with a 1D model built according to the sensitivity tests, for a H2O+N2 atmosphere, to solve the question of the potential overshoot.

 

References

[1] Komabayasi, M. 1967, Journal of the Meteorological Society of Japan. Ser. II

[2] Ingersoll, A. 1969

[3] Nakajima, S., Hayashi, Y.-Y., & Abe, Y. 1992, Journal of the Atmospheric Sciences

[4] Goldblatt, C. & Watson, A. J. 2012, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences

[5] Goldblatt, C., Claire, M. W., Lenton, T. M., et al. 2009, Nature Geoscience

[6] Goldblatt, C., Robinson, T. D., Zahnle, K. J. et al., 2013, Nature Geoscience

[7] Koll, D. D. B. & Cronin, T. W. 2019, The Astrophysical Journal

[8] Leconte, J., Forget, F., Charnay, B. et al., 2013, Nature

[9] Kopparapu, R. k., Ramirez, R., Kasting, J. F., et al. 2013, The Astrophysical Journal

[10] Ramirez, R. M. 2020, Monthly Notices of the Royal Astronomical Society

[11] Zhang, Y. & Yang, J. 2020, The Astrophysical Journal

[12] Pierrehumbert, R. T. 2010, Principles of planetary climate

 

How to cite: Chaverot, G., Bolmont, E., Turbet, M., and Leconte, J.: How does the background atmosphere affect the onset of the runaway greenhouse? Insights from 1D radiative-convective modeling., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2638, https://doi.org/10.5194/egusphere-egu21-2638, 2021.

Super-rotation is a phenomenon in atmospheric dynamics where the specific axial angular momentum of the wind (at some location) in an atmosphere exceeds that of the underlying planet at the equator. Hide's theorem states that in order for an atmosphere to super-rotate, non-axisymmetric disturbances (eddies) are required to induce transport of angular momentum up its local gradient. This raises a question as to the origin and nature of the disturbances that operate in super-rotating atmospheres to induce the required angular momentum transport.

The primary technique employed to investigate this question has involved numerically modelling super-rotating atmospheres, and diagnosing the processes that give rise to super-rotation in the simulations. These modelling efforts can be separated into one of two approaches. The first approach utilises 'realistic', tailor-made models of Solar System atmospheres where super-rotation is present (e.g., Venus and Titan) to investigate the specific processes responsible for generating super-rotation on each planet. The second approach takes simple, 'Earth-like' models, typically dry dynamical cores with radiative transfer represented using a Newtonian cooling approach, and explores the effect of varying a single (or occasionally multiple) planetary parameters (e.g., the planetary radius or rotation rate) on the atmospheric dynamics. Notably, studies of this flavour have shown that super-rotation may emerge 'spontaneously' on planets with slow rotation rate or small radius (relative to the Earth's; Venus and Titan have these characteristics). However, the strength of super-rotation obtained in simulations of this type is far weaker than that observed in Venus' or Titan's atmospheres, or in tailored numerical models of either planet.

In this work, our aim is to bridge the gap between these two modelling approaches. We will present results from a suite of simulations using an idealised general circulation model with a semi-grey representation of radiative transfer. Our experiments explore the effects of varying planetary size and rotation rate, atmospheric mass, and atmospheric absorption of shortwave radiation on the acceleration of super-rotation. A novel aspect of this work is that we vary multiple planetary properties away from their Earth-like 'defaults' in conjunction. This allows us to investigate how properties characteristic of the atmospheres of planets such as Venus and Titan combine to yield the strong super-rotation observed in their atmospheres (and realistic numerical models). We are also able to illustrate how features such as increased atmospheric mass and absorption of shortwave radiation modify the weakly super-rotating state obtained in simple, Earth-like models towards one more characteristic of Titan or Venus.

How to cite: Lewis, N. and Read, P.: Planetary and atmospheric properties leading to strong super-rotation in terrestrial atmospheres studied with a semi-grey GCM, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4855, https://doi.org/10.5194/egusphere-egu21-4855, 2021.

EGU21-15410 | vPICO presentations | PS2.1

Detectability of biosignatures on LHS 1140 b

Fabian Wunderlich, Markus Scheucher, John Lee Grenfell, Franz Schreier, Clara Sousa-Silva, Mareike Godolt, and Heike Rauer

Rocky extrasolar planets orbiting M dwarfs are prime targets in the search for habitable surface conditions and biosignatures with near-future telescopes like the James Webb Space Telescope (JWST) and the Extremely Large Telescope (ELT). Even for the closest known targets the capabilities to characterize Earth-like or CO2-dominated atmospheres with JWST or ELT might still be limited to a few molecules such as CO2 or CH4. Hence it would be difficult to draw conclusions on the surface conditions and potential habitability of these planets. In clear H2-He atmospheres the molecular features in transmission spectra could be much larger and hence potential biosignatures might be detectable.

In this study, we investigate the detectability of the potential biosignatures NH3, PH3, CH3Cl, and N2O, assuming different H2-He atmospheres for the habitable zone super-Earth LHS 1140 b. Recent observations of the atmosphere of LHS 1140 b suggest that the planet might hold a clear H2-dominated atmosphere and might show an absorption feature around 1.4 µm due to H2O or CH4 absorption. Here we use the coupled convective-climate-photochemistry model 1D-TERRA to simulate H2 atmospheres of LHS 1140 b with different amounts of CH4 and assuming that the planet has an ocean and a biosphere.

The destruction of the potential biosignatures NH3, PH3, CH3Cl, and N2O shows a weak dependence on the concentrations of CH4. For weak abundances of CH4 only 5 to 10 transits are required to detect these molecules with JWST or ELT. However, for CH4 surface mixing ratios of a few percent only NH3 and N2O might be detectable with less than 10 transits. A scenario with large abundances of CH4 is consistent with the spectral feature at 1.4 µm and such an atmosphere might allow habitable surface temperatures. If this spectral feature at 1.4 µm originates from H2O absorption, the planet is likely not habitable at the surface.

How to cite: Wunderlich, F., Scheucher, M., Grenfell, J. L., Schreier, F., Sousa-Silva, C., Godolt, M., and Rauer, H.: Detectability of biosignatures on LHS 1140 b, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15410, https://doi.org/10.5194/egusphere-egu21-15410, 2021.

PS3.1 – Small Bodies and Dust — Open Session

EGU21-4186 | vPICO presentations | PS3.1

PMWE creation mechanism inferred from sounding rocket measurements

Boris Strelnikov and the sounding rocket project PMWE team

A first sounding rocket campaign dedicated to investigate the creation mechanism of Polar Mesosphere Winter Echoes (PMWE) was conducted in April 2018 from the north Norwegian Andøya Space Center (69°N, 16°E). Two instrumented sounding rockets were launched on 13th and 18th of April under PMWE and no-PMWE conditions, respectively.

In this paper we give a brief summary of our current knowledge of PMWE and an overview of the PMWE sounding rocket mission. We describe and discuss some results of combined in situ and ground-based measurements which allow to check the existing PMWE theories.

Our measurements clearly show that the coherent structures in refractive index variations (forming PMWE) are accompanied by neutral air turbulence, which is reflected in small-scale structures (down to some meters) of neutral and electron density. We show that the behavior of the structures under investigation together with the atmospheric background is consistent with the interpretation, that PMWE were created by turbulence. Rocket measurements ultimately show that polar winter mesosphere is abounded with meteor smoke particles (MSP) and intermittent turbulent layers. Furthermore, it becomes clear that charged Meteor Smoke Particles (MSP) and background electron density can only enhance SNR, while turbulence is a prerequisite for their formation.

How to cite: Strelnikov, B. and the sounding rocket project PMWE team: PMWE creation mechanism inferred from sounding rocket measurements, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4186, https://doi.org/10.5194/egusphere-egu21-4186, 2021.

EGU21-12636 | vPICO presentations | PS3.1

The Meteoric Ni Layer in the Upper Atmosphere

John Plane, Shane Daly, Wuhu Feng, Thomas Mangan, Michael Gerding, Juan Diego Carrillo Sanchez, and David Bones

The ablation of cosmic dust particles is a source of metallic vapours in planetary upper atmospheres. Recently, ground-based lidars have made the first observations of a layer of Ni atoms peaking around 86 km in the terrestrial atmosphere (in contrast, the layers of Na and Fe have been observed for several decades).  In order to understand these Ni layer observations, we have developed a new version of the Leeds Chemical Ablation Model (CAMBOD) to include a Ni-Fe-S metallic phase in addition to the bulk silicate phase. The validity of the new model was tested using our laboratory Meteoric Ablation Simulator, where micron-size meteoritic particles were flash heated to temperatures as high as 2700 K to simulate their atmospheric entry, and the ablating Ni atoms monitored by fast time-resolved laser induced fluorescence.

The first global atmospheric model of Ni (WACCM-Ni) was then developed with three components: the Whole Atmosphere Community Climate Model (WACCM6); a meteoric input function derived by coupling an astronomical model of dust sources in the solar system with CABMOD; and a comprehensive set of neutral, ion-molecule and photochemical reactions pertinent to the chemistry of Ni in the upper atmosphere. The kinetics of these reactions were mostly measured in our laboratory, or else modelled theoretically using ab initio quantum calculations combined with statistical rate theory. WACCM-Ni simulates satisfactorily the observed neutral Ni layer peak height and width, as well as Ni+ ion measurements from rocket-borne mass spectrometry. The Ni layer is predicted to have a similar seasonal and latitudinal variation as the Fe layer, and its unusually broad bottom-side compared with Fe is caused by the relatively fast NiO + CO → Ni + CO2 reaction. The quantum yield for photon emission from the reaction between Ni and O3, which has been observed in the nightglow from space-based spectrometers, is estimated to be between 6 and 40%.

How to cite: Plane, J., Daly, S., Feng, W., Mangan, T., Gerding, M., Carrillo Sanchez, J. D., and Bones, D.: The Meteoric Ni Layer in the Upper Atmosphere, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12636, https://doi.org/10.5194/egusphere-egu21-12636, 2021.

EGU21-14760 | vPICO presentations | PS3.1

Solving the long-standing problem of estimating the atmospheric temperature at 90 km altitude with meteor radar

Emranul Sarkar, Thomas Ulich, Ilkka Virtanen, Mark Lester, Bernd Kaifler, and Alexander Kozlovsky

For two decades meteor radars have been routinely used to monitor atmospheric temperatures around the 90 km altitude. A common method, based on a temperature-gradient model, is to use the height dependence of meteor decay time to obtain a height-averaged temperature in the peak meteor region. Traditionally this is done by  fitting a linear regression model in the scattered plot of  log10(1/tau) and height, where ’tau’ is the half-amplitude decay time of the received signal. However, this method was found to be consistently biasing the slope estimate. The consequence of such bias is that it produces a  systematic offset in the estimated temperature, and thus requiring calibration with other colocated measurements. The main reason for such a biasing effect is thought to be due to the failure of the classical regression model to take into account the measurement error in decay time or the observed height. This is further complicated by the presence of various geophysical effects in the data, as well as observational limitation in the measuring instruments. We demonstrate an alternative regression method that incorporates various error terms in the statistical model. An initial estimate of the slope parameter is obtained by assuming symmetric error variances in normalised height and log10(1/tau). This solution is found to be a good prior solution for the core of this bivariate distribution. However, depending on the data selection process the error variances may not be exactly equal. A first-order correction is then carried out to address the biasing effect due to asymmetric error variances. This allows to construct an analytic solution for the bias-corrected slope coefficient for this data. With this solution, meteor radar temperatures can be obtained independently without using any external calibration procedure. When compared with colocated lidar measurements, the temperature estimated using this method is found to be accurate within 7% or better and without any systematic offset.

How to cite: Sarkar, E., Ulich, T., Virtanen, I., Lester, M., Kaifler, B., and Kozlovsky, A.: Solving the long-standing problem of estimating the atmospheric temperature at 90 km altitude with meteor radar, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14760, https://doi.org/10.5194/egusphere-egu21-14760, 2021.

EGU21-14249 | vPICO presentations | PS3.1

Meteoroid trajectories from BRAMS data

Hervé Lamy

BRAMS (Belgian RAdio Meteor Stations) is a Belgian radio network using forward scatter observations to detect and characterize meteoroids. A dedicated transmitter located in south of Belgium emits a CW signal with no modulation at a frequency of 49.97 MHz and with a power of 130 W. The network comprises currently 35 similar receiving stations located in Belgium and neighboring countries. They use Yagi antennas with a wide sensitivity pattern which therefore provide no information about the directivity of the meteor echoes. One of these stations is however a radio interferometer using the classical Jones configuration and is able to retrieve the direction of the meteor echoes.

We discuss here a general method to retrieve meteoroid trajectories based solely on time delays measured between meteor echoes recorded at multiple receiving stations. It is based on solving at least 6 non-linear equations to solve for the position of one specular reflection point (3 unknowns) and the 3 components of the speed. This method has also been described recently in Mazur et al (2020) and applied to CMOR data. However, specificities of the CMOR configuration has allowed simplifications that cannot be made with the BRAMS network. In order to maximize the number of meteoroid trajectories with at least 6 stations detecting meteor echoes, a number of additional stations geographically close to each other have been installed in the Limburg province in 2020. Another method to retrieve meteoroid trajectories using data from the radio interferometer and from 3 other stations is also presented.

We show preliminary results from both methods using also complementary data from the optical CAMS Benelux network.  The CAMS trajectories are used to select specific meteor echoes in the BRAMS data. The time delays between them are computed and used to solve the set of non-linear equations to retrieve the meteoroid trajectory and speed, which are then compared to the CAMS values. This allows us to assess the accuracy of both methods.

Finally we simulate the impact of using additional information, not currently available but that might become in a near future. This includes data from a monostatic system (a radar nearby our BRAMS transmitter is currently built), from a second radio interferometer (to be located in Limburg and/or near the transmitter), or the total range traveled by the radio wave if a coded CW transmitter such as in Vierinen et al (2016) is used.

How to cite: Lamy, H.: Meteoroid trajectories from BRAMS data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14249, https://doi.org/10.5194/egusphere-egu21-14249, 2021.

EGU21-14715 | vPICO presentations | PS3.1

Pajala Fireball

Juha Vierinen, Torsten Aslaksen, Jorge Chau, Maria Gritsevich, Björn Gustavsson, Daniel Kastinen, Johan Kero, Alexandre Kozlovsky, Derek McKay, Steinar Midtskogen, Thomas Ulich, and Ketil Vegum

Meteoroids entering the Earth's atmosphere are associated with a number of phenomena including ablation, ambipolar diffusion, plasma transport, chemical reactions, shock waves, and plasma turbulence. A bright daylight fireball observed on 2020-12-04 13:30 UTC with two meteor cameras located in Skibotn and Sørreisa allowed the precise entry trajectory of the fireball to be determined. The path of the entering object is approximately between Angeli Finland and Pajala Sweden. Based on the brightness and entry trajectory, it is possible to estimate the approximate mass of the object, and associate it with a meteor shower (Northern Taurids). The effects of the fireball on the atmosphere were detected with a number of radar and radio instruments within the region, including ionosondes, meteor radars, an all-sky VHF imaging system, and an infrasound sensor. These observations allow a detailed study of the atmospheric interaction of a large meteoric body with the Earth's atmosphere to be made. In this talk, we will describe the observations of this fireball and discuss preliminary findings.

How to cite: Vierinen, J., Aslaksen, T., Chau, J., Gritsevich, M., Gustavsson, B., Kastinen, D., Kero, J., Kozlovsky, A., McKay, D., Midtskogen, S., Ulich, T., and Vegum, K.: Pajala Fireball, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14715, https://doi.org/10.5194/egusphere-egu21-14715, 2021.

EGU21-15687 | vPICO presentations | PS3.1

A composite luminous and dark flight model allowing strewn field prediction

Maria Gritsevich and Jarmo Moilanen

As of today, instrumentally observed meteorite falls account for only 37 recovered meteorite cases, with derived Solar System orbit, out of 65098 registered meteorite names. To bridge this knowledge gap, a number of fireball networks have been set up around the globe. These networks regularly obtain thousands of records of well-observed meteor phenomena, some of which may be classified as a likely meteorite fall (Sansom et al. 2019). A successful recovery of a meteorite from the fireball event often requires that the science team can be promptly directed to a well-defined search area. Here we present a neat Monte Carlo model, which comprises adequate representation of the processes occurring during the luminous trajectory coupled together with the dark flight (Moilanen et al. 2021). In particular, the model accounts for fragmentation and every generated fragment may be followed on its individual trajectory. Yet, the algorithm accounts only for the mass constrained by the observed deceleration, so that the model does not overestimate the total mass of the fragments on the ground (and this mass may also be retrieved as zero). We demonstrate application of the model using historical examples of well-documented meteorite falls, which illustrate a good match to the actual strewn field with the recovered meteorites, both, in terms of fragments’ masses and their spatial distribution on the ground. Moreover, during its development, the model has already assisted in several successful meteorite recoveries including Annama, Botswana (asteroid 2018 LA), and Ozerki (Trigo-Rodríguez et al. 2015, Lyytinen and Gritsevich 2016, Maksimova et al. 2020, Jenniskens et al. 2021).

References

Jenniskens P. et al. (2021). Asteroid 2018 LA, impact, recovery and origin on Vesta. Submitted to Science.

Lyytinen E., Gritsevich M. (2016). Implications of the atmospheric density profile in the processing of fireball observations. Planetary and Space Science, 120, 35-42 http://dx.doi.org/10.1016/j.pss.2015.10.012

Maksimova A.A., Petrova E.V., Chukin A.V., Karabanalov M.S., Felner I., Gritsevich M., Oshtrakh M.I. (2020). Characterization of the matrix and fusion crust of the recent meteorite fall Ozerki L6. Meteoritics and Planetary Science 55(1), 231–244, https://doi.org/10.1111/maps.13423 

Moilanen J., Gritsevich M., Lyytinen E. (2021). Determination of strewn fields for meteorite falls. Monthly Notices of the Royal Astronomical Society, in revision.

Sansom E.K., Gritsevich M., Devillepoix H.A.R., Jansen-Sturgeon T., Shober P., Bland P.A., Towner M.C., Cupák M., Howie R.M., Hartig B.A.D. (2019). Determining fireball fates using the α-β criterion. The Astrophysical Journal 885, 115, https://doi.org/10.3847/1538-4357/ab4516

Trigo-Rodríguez J.M., Lyytinen E., Gritsevich M., Moreno-Ibáñez M., Bottke W.F., Williams I., Lupovka V., Dmitriev V., Kohout T., Grokhovsky V. (2015). Orbit and dynamic origin of the recently recovered Annama’s H5 chondrite. Monthly Notices of the Royal Astronomical Society, 449 (2): 2119-2127, http://dx.doi.org/10.1093/mnras/stv378

How to cite: Gritsevich, M. and Moilanen, J.: A composite luminous and dark flight model allowing strewn field prediction, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15687, https://doi.org/10.5194/egusphere-egu21-15687, 2021.

International cooperation has definitely been shaping the development of the Corpus Juris Spatialis and relative principles under the aegis of the United Nations (see A/Res/1962/XVIII). To this extent, the concept of space as global commons represents the core debate of Space Agencies (ESA), whilst manned and unmanned exploration of the universe are flying to next generation. On the other hand, all space activities will be reasonably linked to both anthropic and natural risks: other effective provisional advancements in international space law are so much needed to addressing space debris and planetary defense as common global challenges

First of all, the space debris issue is susceptible to fostering the aferomentioned level of innovation in space law by these multilateral efforts. All “composite material components” accumulating in considerable amount in Low-Earth Orbit (LEO/collinear Lagrangian points) may possibly lead the way to a comprehensive review of the terms laid down in the Outer Space Treaty (ex plurimis, article IX). Morevover, the further existence of international customary law, which is notably ascertained “as evidence of a general practice accepted as law” (art. 38, let. b, ICJ Statute), might also create hermeneutical tools to tackling such critical task. In addition, a long-term solution may hopefully give birth to the establishment of an international agreement on space debris clearing, providing for adequate international binding norms and structural organization of international guidelines (IADC/UNOOSA) 

Secondly, planetary defense measures vis-à-vis the so called “Cosmic Hazard” shall be carried out by emphasizing the application of international space law and regulations thereto. In particular, the legal use of explosive devices (NED) may be found as slightly critical in light of the applicable international norms and regulations. Moreover, cosmic hazard issues also engage with a very complex level of decision making, to be carried out by a specific vote of the United Nation Security Council (UNSC) in application of the procedure laid down in article 27 of the UN Charter. On the other side, this particular dilemma may call upon States to undertake responses against natural space threats by preventing potential liability of the States (see article VII OST and International Liability Convention for Damages caused by Space Objects)

Eiusmodo, the liability conventional framework shall either have some comprehensive interpretation of the principle of “vis major (quae humana infirmitas resistere non potest)”. In compliance with article II, it must be noticed that failing attempts by Parties- whenever space threats may be encountered in different circumstances  - connects directly with the regime of absolute responsibility for eventual damages occurred to third Parties.

To be concluded, both space debris and planetary defense stand together as resilient pillars of international cooperation in space affairs: the accountable exploration of outer space shall previously take also into account of such perspectives for the exclusive benefit of Mankind  

 

 

How to cite: De Blasi, D.: From space debris to planetary defense: a provisional ground for resilient international cooperation in outer space activities  , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-492, https://doi.org/10.5194/egusphere-egu21-492, 2021.

EGU21-15901 | vPICO presentations | PS3.1

Surface gravimetry on Dimorphos  

Özgür Karatekin, Birgit Ritter, Jose Carrasco, Matthias Noeker, Ertan Umit, Emiel Vanransbeeck, Higinio Alaves, Elisa Tasev, Marta Goli, Stefaan Van waal, and Hannah Goldberg

In the frame work of HERA mission, the gravimeter for small solar system objects (GRASS) has been developed to measure the local acceleration vector on the surface of the moonlet of the binary asteroid, Dimorphos. GRASS will be onboard Juventas CubeSat which is one of the two daughtercraft of ESA’s Hera spacecraft. Launched in 2024 it will arrive in the binary system in 2026. Following the soft-landing of the Juventas CubeSat, GRASS will record the temporal variation of the surface gravity vector.

The average gravitational force expected on the Dimorphos surface is around 5 x 10-5 m s-2 (or 5 mGal). Apart from the self-gravitation of the body, centrifugal forces and the acceleration due to the main body of the system contribute to the surface acceleration. The temporal variations of local gravity vector at the landing site will be used to constrain the geological substructure (mass anomalies, local depth and lateral variations of regolith) as well as the surface geophysical environment (tides, dynamic sloped and centrifugal forces).

We will present the GRASS science objectives in the Hera mission the operational concept that is foreseen to reach these objectives, its current status of development including first test results and the by simulation estimated performances of the instrument.

 

How to cite: Karatekin, Ö., Ritter, B., Carrasco, J., Noeker, M., Umit, E., Vanransbeeck, E., Alaves, H., Tasev, E., Goli, M., Van waal, S., and Goldberg, H.: Surface gravimetry on Dimorphos  , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15901, https://doi.org/10.5194/egusphere-egu21-15901, 2021.

EGU21-14898 | vPICO presentations | PS3.1

Didymos Gravity Science Investigations through Ground-based and Inter-Satellite Links Doppler Tracking

Paolo Tortora, Marco Zannoni, Edoardo Gramigna, Riccardo Lasagni Manghi, Sebastien Le Maistre, Ryan S. Park, Giacomo Tommei, Ozgur Karatekin, Hannah Goldberg, Paolo Martino, Paolo Concari, Michael Kueppers, Patrick Michel, and Ian Carnelli

The Asteroid Impact and Deflection Assessment (AIDA) is an international collaboration supported by ESA and NASA to assess the feasibility of the kinetic impactor technique to deflect an asteroid, combining data obtained from NASA’s DART and ESA’s Hera missions. Together the missions represent the first humankind’s investigations of a planetary defense technique. In 2022, DART will impact Dimorphos, the secondary of the binary near-Earth asteroid (65803) Didymos.  After 4 years, Hera will follow-up with a detailed post-impact survey of Didymos, to fully characterize and validate this planetary defense technique. In addition, Hera will deploy two CubeSats around Didymos once the Early Characterization Phase has completed, to augment the observations of the mother spacecraft. Juventas, the first Cubesat, will complete a low-frequency radar survey of the secondary, to unveil its interior. Milani, the second Cubesat, will perform a global mapping of Didymos and Dimorphos, with a focus on their compositional difference and their surface properties. One of the main objectives of Hera is to determine the binary system’s mass, gravity field, and dynamical state using radio tracking data in combination with imaging data. The gravity science experiment includes classical ground-based radiometric measurements between Hera and ground stations on Earth by means of a standard two-way X-band link, onboard images of Didymos, and spacecraft-to-spacecraft inter-satellite (ISL) radiometric tracking between Hera and the Cubesats. The satellite-to-satellite link is a crucial add-on to the gravity estimation of low-gravity bodies by exploiting the Cubesats’ proximity to the binary, as the range-rate measurements carried out by the inter-satellite link contain information on the dynamics of the system, i.e., masses and gravity field of Didymos primary and secondary.

We will describe the updated mission scenario for the Hera radio science experiment to be jointly carried out by the three mission elements, i.e., Hera, Juventas and Milani. To conclude, our updated analysis and latest results, as well as the achievable accuracy for the estimation of the mass and gravity field of Didymos and Dimorphos, are presented.

How to cite: Tortora, P., Zannoni, M., Gramigna, E., Lasagni Manghi, R., Le Maistre, S., Park, R. S., Tommei, G., Karatekin, O., Goldberg, H., Martino, P., Concari, P., Kueppers, M., Michel, P., and Carnelli, I.: Didymos Gravity Science Investigations through Ground-based and Inter-Satellite Links Doppler Tracking, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14898, https://doi.org/10.5194/egusphere-egu21-14898, 2021.

EGU21-79 | vPICO presentations | PS3.1

The large-scale troughs on Asteroid 4 Vesta are opening-mode fractures

Hiu Ching Jupiter Cheng and Christian Klimczak

The Dawn mission at Asteroid 4 Vesta revealed two sets of enormous linear structures. Both sets are troughs—linear, negative-relief landforms—with one spanning around at least two-thirds of the equator and the other set incompletely preserved in the northern hemisphere. A previous study evaluated the cross-sectional geometries of the troughs and interpreted them as analogous to grabens, which are landforms caused by normal faults. However, for the troughs to be large-scale opening-mode fractures, i.e., joints, was heretofore not considered. To distinguish between normal faulting and jointing, we investigated the map patterns, cross-sectional geometries, and variations of relief and width along the length of these troughs. Relief and width are meaningful measurands that causally relate to the vertical displacement of faults or aperture of joints, respectively. Their distributions along the trough length should thus reveal differences in fracturing behavior. In addition, we derived strength-depth profiles to characterize the rheologic structure of Vesta’s lithosphere and determine the predicted fracturing behavior in its brittle regime.

We mapped all large-scale troughs on Vesta, including four equatorial and two northern troughs, and no map patterns diagnostic for faulting were identified. The troughs are bounded by scalloped rims and mainly show V- and bowl shapes in cross-section. The variation of reliefs of the two-opposing trough-bounding scarps reveals that the relief maxima for each of the investigated troughs are located off-center, and at different locations along the trough they bound. In contrast, we found that both the individual and cumulative variations in trough width have their maxima near the center of the trough. These map patterns and geomorphologic characteristics are largely inconsistent with the mechanics of graben formation but instead point to an origin by opening-mode fracturing. Moreover, our calculations of lithospheric strength evolution that enable assessments of fracturing behavior reveal that Vesta’s lithosphere has been dominated by a thick brittle portion throughout its history. Solutions to the Coulomb criterion considering a range of strengths properties of intact to fractured basaltic materials are in support of jointing as the major fracturing mode in at least the upper ~14 km of Vesta’s lithosphere.

How to cite: Cheng, H. C. J. and Klimczak, C.: The large-scale troughs on Asteroid 4 Vesta are opening-mode fractures, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-79, https://doi.org/10.5194/egusphere-egu21-79, 2021.

EGU21-14167 * | vPICO presentations | PS3.1 | Highlight

Hayabusa2 returned samples: first analyses from the MicrOmega/curation investigation 

Jean-Pierre Bibring, Tatsuaki Okada, Cédric Pilorget, Kasumi Yogata, Rosario Brunetto, Lucie Riu, Vincent Hamm, Aiko Nakato, Kentaro Hatakeda, Damien Loizeau, Toru Yada, and and the MicrOmega team

The JAXA Hayabusa2 mission has very impressively collected and returned more than 5 g of samples from the C-type Ryugu asteroid early December, 2020, all presently secured within the Extraterrestrial Sample Curation Center at ISAS, Sagamihara, Japan. Their characterization is being performed, using an optical microscope, a FTIR point spectrometer and MicrOmega, a hyperspectral microscope acquiring from each 22 µm pixel of its 256x250 pixels FOV, the full spectrum from 0.99 to 3.6 µm (+ 4 additional visible spectral channels, at 595, 643, 770 and 885 nm). Preliminary results acquired with MicOmega will be presented, and their interpretation discussed.

How to cite: Bibring, J.-P., Okada, T., Pilorget, C., Yogata, K., Brunetto, R., Riu, L., Hamm, V., Nakato, A., Hatakeda, K., Loizeau, D., Yada, T., and MicrOmega team, A. T.: Hayabusa2 returned samples: first analyses from the MicrOmega/curation investigation , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14167, https://doi.org/10.5194/egusphere-egu21-14167, 2021.

EGU21-14559 | vPICO presentations | PS3.1

Multifluid modelling of cometary coma for diverse range of parent volatile compositions

Sana Ahmed and Kinsuk Acharyya

Comets show a general diversity in their parent volatile composition, but in most cases H2O is observed to be the dominant volatile in terms of abundance. This is followed by CO and CO2, and trace amounts of other species such as CH4, CH3OH, O2, and NH3 are also present. However, the observed ratio of n_x/H2O varies considerably from one comet to another (n_x represents any parent species other than water).

We aim to study how the chemistry and dynamics of the cometary coma changes for varying abundances of the major parent volatiles. We have constructed a fluid model, using the principles of conservation of mass, momentum and energy, for our study. Parent volatiles sublimating from the nucleus undergo photolytic reactions due to the solar UV radiation field, resulting in the formation of secondary neutral and ionic species and photoelectrons. Active chemistry occurs in the coma, and some of the chemical reactions taking place are ion-neutral rearrangement, charge exchange, dissociative recombination, electron impact dissociation and radiative de-excitation. The energy that is released due to these chemical reactions is non-uniformly distributed amongst all the species, resulting in different temperatures. Hence,  for a complete description of the coma, we have used a multifluid model whereby the neutrals, ions and electrons are considered as three separate fluids. Apart from chemical reactions, we have also considered the exchange of energy between the three fluids due to elastic and inelastic collisions.

We consider different initial compositions of the comet, and then use our model to generate the temperature and velocity profiles of the coma, for varying cometocentric distances. We also obtain the number density profiles of the different ionic and neutral species that are created in the coma. We see that changes in the initial parent volatile abundance will modify the temperature profile, and there are significant changes in the ionic abundances. Hence, the parent volatile composition of the comet drives the physico-chemical attributes of the coma.

How to cite: Ahmed, S. and Acharyya, K.: Multifluid modelling of cometary coma for diverse range of parent volatile compositions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14559, https://doi.org/10.5194/egusphere-egu21-14559, 2021.

EGU21-9244 | vPICO presentations | PS3.1

Abel transform of exponential functions for planetary and cometary atmospheres with application to observation of 46P/Wirtanen and to the OI 557.7 nm emission at Mars.

Benoit Hubert, Guy Munhoven, Youssef Moulane, Damien Hutsemekers, Jean Manfroid, Cyrielle Opitom, Emmanuel Jehin, Shohei Aoki, Lauriane Soret, Leonardos Gkouvelis, and Jean-Claude Gérard

Line-of-sight integration of emissions from planetary and cometary atmospheres is the Abel transform of the emission rate, under the spherical symmetry assumption. Indefinite integrals constructed from the Abel transform integral are useful for implementing remote sensing data analysis methods, such as the numerical inverse Abel transform giving the volume emission rate compatible with the observation. We obtain analytical expressions based on a suitable, non-alternating, series development to compute those indefinite integrals. We establish expressions allowing absolute accuracy control of the convergence of these series depending on the number of terms involved. We compare the analytical method with numerical computation techniques, which are found to be sufficiently accurate as well. Inverse Abel transform fitting is then tested in order to establish that the expected emission rate profiles can be retrieved from the observation of both planetary and cometary atmospheres. We show that the method is robust, especially when Tikhonov regularization is included, although it must be carefully tuned when the observation varies across many orders of magnitude. A first application is conducted over observation of comet 46P/Wirtanen, showing some variability possibly attributable to an evolution of the contamination by dust and icy grains. A second application is considered to deduce the 557.7 nm volume emission rate profile of the metastable oxygen atom in the upper atmosphere of planet Mars.

How to cite: Hubert, B., Munhoven, G., Moulane, Y., Hutsemekers, D., Manfroid, J., Opitom, C., Jehin, E., Aoki, S., Soret, L., Gkouvelis, L., and Gérard, J.-C.: Abel transform of exponential functions for planetary and cometary atmospheres with application to observation of 46P/Wirtanen and to the OI 557.7 nm emission at Mars., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9244, https://doi.org/10.5194/egusphere-egu21-9244, 2021.

EGU21-1719 | vPICO presentations | PS3.1

Analyzing 67P’s dusty coma

Nora Hänni, Kathrin Altwegg, Daniel Müller, Boris Pestoni, Martin Rubin, and Susanne Wampfler

While the volatile species in comet 67P/Churyumov-Gerasimenko’s coma have been analyzed in great spatial and temporal detail, e.g., Rubin et al. (2019) or Läuter et al. (2020), little is so far known about the less volatile, heavier species. There is growing evidence, however, that less volatile species, such as salts, may play a key role in explaining some of the puzzling properties of comets, as for instance shown by Altwegg et al. (2020). These authors also have demonstrated the unique capability of ROSINA/DFMS (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis/ Double Focusing Mass Spectrometer; Balsiger et al. (2007)) to detect exactly such little volatile species in-situ, namely during a dust event on 5 September 2016 (when a dust grain entered the instrument and sublimated inside).

Complementary information on 67P’s dusty coma can be obtained from data collected during time periods of high dust activity. A clear advantage of such data is they also allow for a quantitative interpretation thanks to the much more stable measurement conditions. Moreover, a comparison to data collected during a time period of little dust activity (e.g., to the days around end of May 2015 as in Rubin et al. 2019) also allows to link species to dust.

End of July / beginning of August 2015, the comet was approaching its perihelion and ejecting a lot of dust, as seen by the OSIRIS camera (Vincent et al. 2016). The data from this period are therefore a promising starting point for the search of heavier species (m > 100 Da). Altwegg et al. (2019), for instance, reported on the tentative identifications of the simplest polyaromatic hydrocarbon species naphthalene as well as of benzoic acid, the simplest aromatic carboxylic acid. To confirm these identifications and to achieve a more complete inventory of heavier and chemically more complex species, we are now analyzing these data sets strategically. In our contribution we will share what we have learned from pushing the exploration of 67P’s dusty coma.

 

Altwegg et al., 2020, Nat. Astron., 4, 533-540.
Altwegg et al., 2019, Annu. Rev. Astron. Astrophys., 57, 113-55.
Balsiger H. et al., 2007, Space Sci. Rev., 128, 745-801.
Läuter et al., 2020, MNRAS, 498, 3, 3995-4004.
Rubin et al., 2019, MNRAS, 489, 594-607. Vincent et al., 2016, MNRAS, 462 (Suppl_1), 184-194.

How to cite: Hänni, N., Altwegg, K., Müller, D., Pestoni, B., Rubin, M., and Wampfler, S.: Analyzing 67P’s dusty coma, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1719, https://doi.org/10.5194/egusphere-egu21-1719, 2021.

EGU21-10601 | vPICO presentations | PS3.1

Chlorine-bearing species and the 37Cl/35Cl isotope ratio in the coma of comet 67P/Churyumov-Gerasimenko

Frederik Dhooghe, Johan De Keyser, Nora Hänni, Kathrin Altwegg, Gaël Cessateur, Emmanuel Jehin, Martin Rubin, and Peter Wurz

A full-mission analysis of Cl-bearing species in the coma of comet 67P/Churyumov-Gerasimenko has been conducted using data from the Rosetta ROSINA/DFMS mass spectrometer. This contribution will focus on the challenges encountered to relate DFMS data on Cl-bearing species to the neutral abundances at the comet.

DFMS was operated in neutral mode, in which electron impact ionizes a fraction of the incoming neutral gas in the ion source. Only ions in a narrow range around a certain commanded mass-over-charge ratio (m/z) pass through the mass analyser at a time and impact on a micro-channel plate (MCP), creating an electron avalanche that is recorded by a Linear Electron Detector Array chip with two rows of 512 pixels each (LEDA A and LEDA B). Data are obtained as Analog-to-Digital Converter (ADC) counts as a function of LEDA pixel number. The instrument scans over a sequence of m/z values.

A well-defined approach exists to convert ADC counts as a function of pixel number to the number of ions that were detected on the MCP. However, to relate the number of ions detected this way to the abundance of neutrals in the coma gas, the sensitivity for each neutral needs to be known. The sensitivity for a certain neutral takes into account the total ionization cross section for the neutral and product ion fraction, instrument transmission and secondary electron yield for each product ion. Sensitivities can be determined experimentally by introducing the neutrals in the DFMS instrument copy in the laboratory, but such data are not available for Cl-bearing species and an alternative approach needs to be used. Fortunately, the use of ratios cancels out some of the factors that play a role in the sensitivity. As an example, for the 37Cl/35Cl ratio, total ionization cross sections and product ion fractions can be considered identical. In the case of 37Cl/35Cl, taking into account the sensitivity results in a correction of more than 15%, mainly due to the secondary electron yield.

The 37Cl/35Cl ratio does not appear to change appreciably throughout the mission and is compared with known values from other solar system objects. The Cl/HCl ratio obtained with DFMS indicates that there must be at least one additional chlorine-bearing species on the comet next to HCl, CH3Cl and NH4Cl, the identity of which is unknown at this time.

How to cite: Dhooghe, F., De Keyser, J., Hänni, N., Altwegg, K., Cessateur, G., Jehin, E., Rubin, M., and Wurz, P.: Chlorine-bearing species and the 37Cl/35Cl isotope ratio in the coma of comet 67P/Churyumov-Gerasimenko, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10601, https://doi.org/10.5194/egusphere-egu21-10601, 2021.

EGU21-14765 | vPICO presentations | PS3.1

Accurate ephemeris reconstruction for comet 67P/Churyumov-Gerasimenko from Rosetta data analysis

Riccardo Lasagni Manghi, Marco Zannoni, Paolo Tortora, Michael Küppers, Laurence O'Rourke, Patrick Martin, Stefano Mottola, Frank Budnik, Ruaraidh Mackenzie, Bernard Godard, Laurent Jorda, Olivier Groussin, and Nicolas Thomas

Following its arrival at 67P/Churyumov-Gerasimenko in August 2014, the Rosetta spacecraft successfully navigated in proximity of the comet for two years, using a combination of radiometric measurements and optical images collected by the onboard navigation cameras.

The reconstructed spacecraft and comet trajectories were obtained combining several long-arc and short-arc orbit determination solutions generated by ESOC Flight Dynamics during the Rosetta operations. Several discontinuities are present within these trajectories, due to the lack of a dynamical model for the representation of the comet Non-Gravitational Accelerations (NGA).

The work presented in this study represents an effort to produce an accurate and continuous ephemeris reconstruction for comet 67P/Churyumov-Gerasimenko for the period between July 2014 and October 2016, through a complete reanalysis of the Range and ΔDOR measurements collected by Rosetta during its proximity phase with the comet.

Using as input the reconstructed relative orbit of Rosetta, the radiometric observables were mapped to the comet nucleus and used to estimate the comet state and some key physical and observational parameters within a Square Root Information batch filter implemented in MONTE, most notably the NGA acting on the comet nucleus due to surface outgassing.

Several orbit determination solutions were generated by varying the model used to represent the NGA. More specifically, empirical and stochastic models were compared by evaluating the reduced χ2 statistics of the measurement residuals to identify the most suitable trajectory estimations for each of the proposed models. From this narrow list of solutions, a preliminary selection for the final ephemeris reconstruction is proposed, based on its adherence to the original ESOC trajectory and on the consistency of the formal state uncertainties with the estimated solutions.

It will be shown that the selected ephemeris solution, using a piecewise linear stochastic NGA model with intervals between 3 and 4 weeks, produces a continuous ephemeris reconstruction for 67P/Churyumov-Gerasimenko with maximum formal uncertainties around perihelion of σpos ≅ [20 km, 30 km, 200 km] in the Radial-Tangential-Normal reference frame. The advantage of using simple stochastic models, with limited a-priori assumptions on the involved physical processes, is that they allow to produce an unbiased estimation of the NGA variations around perihelion, which represent a valuable input for further investigations involving detailed physical models of the cometary activity.

How to cite: Lasagni Manghi, R., Zannoni, M., Tortora, P., Küppers, M., O'Rourke, L., Martin, P., Mottola, S., Budnik, F., Mackenzie, R., Godard, B., Jorda, L., Groussin, O., and Thomas, N.: Accurate ephemeris reconstruction for comet 67P/Churyumov-Gerasimenko from Rosetta data analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14765, https://doi.org/10.5194/egusphere-egu21-14765, 2021.

EGU21-10426 | vPICO presentations | PS3.1

In the context of Comet Interceptor: Unexpected polarimetric properties of some dust particles in cometary comae and on small bodies surfaces

A.Chantal Levasseur-Regourd, Edith Hadamcik, Jérémie Lasue, Julien Milli, and Jean-Baptiste Renard

The ESA-JAXA Comet Interceptor mission is expected to flyby a dynamically new comet (or an interstellar one) and better reveal the properties of its dust particles and nucleus surface. We therefore tentatively compare polarimetric properties of dust released by some comets, as well as present on surfaces of some small bodies.

Phase curves of the linear polarization of cometary dust particles (observed in equivalent wavelength ranges) show analogous trends. Some unique dynamically new comets or fragmenting comets (e.g. C/1995 O1 Hale-Bopp, C/1999 S4 LINEAR) may nevertheless present a higher positive branch than Halley-type or Jupiter-family comets (e.g. 1P/Halley, 67P/Churyumov-Gerasimenko). Such differences are clues to differences in the properties (sizes, morphologies, complex optical indices) of the dust particles. Dust particles, ejected by nuclei frequently plunging in the inner Solar System, might indeed partly come from quite dense a surface layer, as detected on the small lobe of comet 67P by Rosetta [1].

Although polarimetric observations of surfaces of cometary nuclei are almost impossible, observations of the rather quiescent nucleus of 1P/Encke have been obtained [2].  Similarities between polarimetric properties of 1P/Encke and atypical small bodies (e.g. Phaeton and particularly Bennu [3]), and of dust in cometary comae may be pointed out. Numerical and laboratory simulations could represent a unique tool to better understand such similarities. It may also be added that dust particles originating from comets, with emphasis on those of Jupiter-family, may survive atmospheric entry, as CP-IDPs collected in the Earth’s stratosphere, and that dust found in debris disks of stellar systems shows levels of polarization similar to those of highly-polarized comets [4].

 

[1] Kofman et al., MNRAS, 497, 2616-2622, 2020, [2] Boehnhardt et al., A&A, 489, 1337-1343, 2008. [3] Cellino et al., MNRAS, 481, L49-L53, 2018. [4] Levasseur-Regourd et al., PSS, 186, 104896, 2020,

 

How to cite: Levasseur-Regourd, A. C., Hadamcik, E., Lasue, J., Milli, J., and Renard, J.-B.: In the context of Comet Interceptor: Unexpected polarimetric properties of some dust particles in cometary comae and on small bodies surfaces, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10426, https://doi.org/10.5194/egusphere-egu21-10426, 2021.

EGU21-8959 | vPICO presentations | PS3.1

Dust Grain Detection by Solar Orbiter, Parker Solar Probe, and Magnetospheric Multiscale (MMS) Mission — Similarities and Differences

Jakub Vaverka, Jiří Pavlů, Libor Nouzák, Samuel Kočiščák, Jana Šafránková, Zdeněk Němeček, David Píša, Jan Souček, Arnaud Zaslavsky, Ingrid Mann, Milan Maksimovic, Stuart Bale, and Per-Arne Linqvist

The dust impact detection by electric field instruments is already a well-established technique. On the other hand, not all aspects of signal generation by dust impacts and its consequent detection are completely understood and explained. It has been shown that the design and configuration (monopole/dipole) of the electric field antennas/probes are very important for dust impact detection and understanding of the measured signal. Therefore, it is not straightforward to compare detected signals by various spacecraft. Most of space missions use at the same time either monopole or dipole antenna configuration. However, the MMS simultaneous monopole and dipole measurements provide us with interesting information about dust impact signals. We have analyzed individual electric field waveforms of dust impacts detected by Solar Orbiter, Parker Solar Probe, and MMS to understand similarities and differences of dust detection by various spacecraft with different antenna designs and configurations. This understanding will allow us to reliably compare obtained dust fluxes among individual missions.  

How to cite: Vaverka, J., Pavlů, J., Nouzák, L., Kočiščák, S., Šafránková, J., Němeček, Z., Píša, D., Souček, J., Zaslavsky, A., Mann, I., Maksimovic, M., Bale, S., and Linqvist, P.-A.: Dust Grain Detection by Solar Orbiter, Parker Solar Probe, and Magnetospheric Multiscale (MMS) Mission — Similarities and Differences, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8959, https://doi.org/10.5194/egusphere-egu21-8959, 2021.

EGU21-12698 | vPICO presentations | PS3.1

Ambipolar electrostatic field in negatively charged dusty plasma

Lina Hadid, Oleg Shebanits, Jan-Erik Wahlund, Michiko Morooka, Andrew Nagy, William M. Farrell, Mika Holmberg, Ronan Modolo, Ann Persoon, and Wendy Tseng

EGU21-14909 | vPICO presentations | PS3.1

The Effective Temperature of Dust Impact Plasmas — Olivine Dust on Tungsten Target

Jiří Pavlů, Samuel Kočiščák, Åshild Fredriksen, Michael DeLuca, and Zoltan Sternovsky

We experimentally observe both positive and negative charge carriers in impact plasma and estimate their effective temperatures. The measurements are carried on a dust accelerator using polypyrrole (PPy)-coated olivine dust particles impacting tungsten (W) target in the velocity range of 2–18 km/s. We measure the retained impact charge as a function of applied bias potential to the control grid. The temperatures are estimated from the data fit. The estimated effective temperatures of the positive ions are approximately 7 eV and seems to be independent of the impact speed. The negative charge carriers' temperatures vary from as low as 1 eV for the lowest speeds to almost ten times higher speeds. The presented values differ significantly from previous studies using Fe dust particles. Yet, the discrepancy can be attributed to a larger fraction of negative ions in the impact plasma that likely originates from the PPy coating.

How to cite: Pavlů, J., Kočiščák, S., Fredriksen, Å., DeLuca, M., and Sternovsky, Z.: The Effective Temperature of Dust Impact Plasmas — Olivine Dust on Tungsten Target, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14909, https://doi.org/10.5194/egusphere-egu21-14909, 2021.

EGU21-11161 | vPICO presentations | PS3.1

Interpretation of dust impact signals detected by Cassini at Saturn

Libor Nouzak, Jiří Pavlů, Jakub Vaverka, Jana Šafránková, Zdeněk Němeček, David Píša, Mitchell H. Shen, Zoltan Sternovsky, and Shengyi Ye

The Cassini spacecraft spent more than 13 years in the dusty environment of Saturn. During this long period of investigations of the Saturn magnetosphere, the RPWS (Radio Plasma Wave Science) instrument recorded more than half a million spiky signatures. However, not all of them can be interpreted as dust impact signals because plasma structures like solitary waves can result in similar pulses.

We select the registered spike waveforms recorded by both dipole and monopole configurations of electric field antennas operated in 10 kHz or 80 kHz sampling rates at the distance of 0.2 Rs around the rings mid-plane. These waveforms were corrected using Cassini WBR (Wide Band Receiver) transfer function to obtain the correct shape of the signal. The signal polarity, amplitude, and timescales of different parts of the waveforms were quantitatively inspected according to the spacecraft potential, the density of the ambient plasma, the intensity of the Saturn’s magnetic field, and its orientation with respect to the spacecraft. The magnetic field orientation was also used for distinguishing between signals resulting from dust impacts and signals produced by solitary waves misinterpreted as dust impact signals.

The preliminary results of our study indicate similarities with previous laboratory studies of dust impact waveforms on the reduced model of Cassini bombarded with submicron-sized iron grains in external magnetic fields at the LASP facility of the University of Colorado. The polarity of the signals changes in accordance with a polarity of the spacecraft potential and pre-spike signals are also observed. The core of the paper is devoted to the relation between characteristics of dust impact signals and local plasma parameters and magnetic field intensity at the radial distance from 2 Rs to 60 Rs from Saturn surface.

How to cite: Nouzak, L., Pavlů, J., Vaverka, J., Šafránková, J., Němeček, Z., Píša, D., Shen, M. H., Sternovsky, Z., and Ye, S.: Interpretation of dust impact signals detected by Cassini at Saturn, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11161, https://doi.org/10.5194/egusphere-egu21-11161, 2021.

EGU21-3519 | vPICO presentations | PS3.1

Flattening of ring particles and self-gravity wakes in Saturn’s rings

Larry W. Esposito, Miodrag Sremcevic, Joshua Colwell, Stephanie Eckert, and Richard Jerousek

The varying geometry of Cassini star occultations by Saturn’s rings constrains both the size and shape of structures that block starlight. Statistics of UVIS star occultations measure structures as small as meters, on times scales of minutes to decades. We calculate the excess variance, skewness and kurtosis including the effects of irregular particle shadows, along with a granola bar model of gaps, ghosts and clumps. The widths W and separation S of rectangular clumps play an analogous role to the relative size of the particle shadows, δ. In the first model considered, our calculations are based on the moments of the transparency T in that part of the ring sampled by the occultation, thus extending the work of  Showalter and Nicholson (1990) to larger τ  and δ, and to higher central moments, without their simplifying assumptions. We also calculate these statistics using an approach based on the autocovariance, autocoskewness and autocokurtosis.

These new approaches compare well to the formula for excess variance from Showalter and Nicholson in the region where all are accurate, δτ1. Skewness for small τ has a different sign for transparent and opaque structures, distinguishing gaps from clumps. The higher order central moments are more sensitive to the extremes of the size distribution and opacity.

We explain the upward curvature of the dependence of normalized excess variance for Saturn’s background C ring by the observation of Jerousek etal (2018) that the measured optical depth is correlated with particle size. For a linear dependence Reff = 12 * (τ – 0.08) + 1.8m from Jerousek’s results, we match the curvature of normalized excess variance, the skewness and the kurtosis in the region between 78,000 and 84,600km from Saturn.

Statistics calculated from the granola bar model give different predictions from individual particles. The different τ dependence suggests that the wave crests compress the gaps more than the wakes, and produce more regularity among the clumps; and larger and more opaque self-gravity wakes in the wave crests, with transparent ghosts. The UVIS observations fall between the most regular and the most irregular granola bar models.

We compare selected occultations (Eckert etal 2020) at different values of the elevation B to estimate the flattening and axial ratio of ring particles and clumps. In Ring C, we find spheres: The statistical measures from multiple occultations follow the expected dependence on sin B, e.g. Showalter & Nicholson (1990). However, in the Janus 2:1 and Mimas 5:3 density waves, the excess variance for stars β Cen, λ Sco and σ Sgr shows no B dependence. This is exactly the expectation for completely flat (H/W =0) self-gravity wakes that we have derived from the autocovariance of the wake shadows. A closer analysis of this particular case gives H/W < 0.04, different from Colwell etal (2007), suggesting wakes are more like linguine than granola bars.

How to cite: Esposito, L. W., Sremcevic, M., Colwell, J., Eckert, S., and Jerousek, R.: Flattening of ring particles and self-gravity wakes in Saturn’s rings, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3519, https://doi.org/10.5194/egusphere-egu21-3519, 2021.