EXOA6 | Planetary Atmospheres: a key to the evolution of planets


Planetary Atmospheres: a key to the evolution of planets
Co-organized by TP/OPS
Convener: Ann Carine Vandaele | Co-conveners: Giuliano Liuzzi, Yeon Joo Lee, Cédric Gillmann, Anne Grete Straume-Lindner
| Tue, 10 Sep, 14:30–16:00 (CEST)|Room Saturn (Hörsaal B)
| Attendance Tue, 10 Sep, 10:30–12:00 (CEST) | Display Tue, 10 Sep, 08:30–19:00
Orals |
Tue, 14:30
Tue, 10:30
Over the last decades, we have been getting closer to characterizing the atmospheres of exoplanets. This has sparked renewed investigations of how planetary atmospheres could act as a tracer of the evolution of planets as a whole system. Advances in planetary science have revealed an incredible diversity of possible atmospheres on the various planetary bodies in our galaxy and through time. Considerable efforts are being made at international level to better understand such diverse atmospheres and the driving forces behind their evolution. This session welcomes presentations regarding how our knowledge of current planetary atmospheres can shed light on their evolutionary paths. How can the exploration of planetary atmospheres inform about the history of planet formation, their long-term climate, and the interaction between atmosphere, surface, interior and volatile reservoirs?

Orals: Tue, 10 Sep | Room Saturn (Hörsaal B)

Virtual presentation
Bruce Jakosky

Introduction:  Understanding exoplanet habitability and its evolution requires understanding the relative importance of the different sinks for atmospheric volatiles.  While a lot of attention is paid to stripping of atmospheric gas by stellar EUV and stellar winds, geological and geochemical processes also can have a major affect volatiles.  This is demonstrated with the example of volatile sources and sinks for Mars.  Mars has undergone significant stripping of gas to space, but also has lost gas and had gas supplied by multiple other processes.  We focus here on CO2 and H2O as the most-relevant volatiles for climate and habitability. 

Martian CO2: CO2 has been the most important greenhouse gas for Mars, although other gases may be important as well. 

Supply of CO2 to the atmosphere and near-surface region involves early catastrophic outgassing and release from the mantle through volcanism or as gas dissolved in water released to the surface.

Loss of an early, thicker CO2 atmosphere to get to today’s 6-mbar atmosphere was driven by the following processes:

- Impact ejection to space during the tail end of planetary accretion and heavy bombardment.

- Stripping to space by the early EUV and the solar wind and solar storms, all of which were more intense than today.

- Storage in the polar ice caps, which is thought to contain the equivalent of ~6 mbar of CO2 today.

- Storage as H2O-CO2 clathrate hydrate, possibly present in the polar caps or high-latitude ground ice.

- Formation of near-surface carbonate minerals that can store CO2 in mineral form.

- Sequestration in the form of gas adsorbed onto regolith grains, which depends on the composition and thickness of the regolith.

- Deep-crustal carbonates, revealed where impacts or tectonic processes have exposed them.

Together, these sinks can account for a minimum of 1.5 bars of CO2 from an early atmosphere, with roughly half of the CO2 having gone to sinks other than loss to space.

Martian H2O:  Evidence points to Mars having had much more water at its surface early in its history.  The figure shows the range of potential processes that control the evolution of Martian H2O.

Supply of H2O to the atmosphere and near-surface region results from early catastrophic release as a result of planetary formation, differentiation, early crustal formation, and release from late-accreted material up until ~3.7 b.y.a.  In addition, water has been supplied by volcanism through time, and has been stored in the crust and released by catastrophic flooding.

Loss of Martian water was driven by the following processes:

- Sequestration in the polar caps and high-latitude ground ice, thought to be capable of exchanging with today’s atmosphere on various timescales.

- Loss to space, via photodissociation and escape of the atomic H and O and of molecular H2.

- Incorporation into minerals as water of hydration, oxidation, or adsorbed gas, with the minerals being identified and mapped today.

- Potential buried water ice, from an early ocean if the water did not evaporate back into the atmosphere.

- Free liquid water or ice sequestered in the crust or megaregolith, based on water released in the catastrophic floods that drained only a tenth of the crust.

These sinks can account for removal of ~400-2000 m H2O (global equivalent layer), with loss to space accounting for ~100-500 m.  For comparison, today’s atmosphere holds the equivalent of about 10 micrometers of water if it all were condensed onto the surface.

Discussion:  Clearly, evolution of Mars’ climate and habitability depends on more than just stripping of gas to space by the host star.  For Mars, the geological and geochemical processes of removing gas are important and may have dominated the total volatile loss; these sinks also can store gas and later release it back into the atmosphere.  (Additional processes may operate on exoplanets that have not operated on Mars, e.g., involving plate tectonics.)  There’s no reason to think that exoplanets will have the same relative importance of each process as does Mars.  However, processes intrinsic to a planet have to be considered as a key part of volatile and climate evolution. Even with the three very different examples of Earth, Venus, and Mars, we cannot predict the geologically driven behavior of volatiles on a rocky planet; clearly, however, these processes could dominate the evolution of exoplanet atmospheres and habitability


How to cite: Jakosky, B.: Evolution of exoplanet atmospheres:  The Mars example of geological sources and sinks in addition to solar/stellar stripping of gas, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-497, https://doi.org/10.5194/epsc2024-497, 2024.

On-site presentation
Ashwin Braude, Laura Kerber, Franck Lefèvre, Yassin Jaziri, Saira Hamid, Maxime Maurice, Maxence Lefèvre, Ehouarn Millour, and François Forget

Introduction:  Although Mars is now a cold, dry planet, the geological record shows that, early in its history, Mars not only went through episodes of wet-dry cycling [1], in which Mars could maintain liquid water on its surface for sustained periods of time, but was also volcanically active [2]. As a high-pressure CO2 and H2O atmosphere alone could not induce the required annually-averaged temperatures for liquid water given the brightness of the Sun at the time [3,4], one hypothesis suggested sulphur dioxide (SO2) and hydrogen sulphide (H2S) emitted by active volcanoes on the surface of Mars as a source of greenhouse warming [5]. Later studies then suggested that any greenhouse warming from SO2and H2S would be negated by the cooling effect of sulphuric acid (H2SO4) and elemental polysulphur (S8) clouds that would result from the reaction of SO2and H2S with water vapour in the atmosphere. However, these studies either relied on photochemical models in 1-D [6,7], which neglect spatial variations in cloud formation, or simple parametrisations of sulphur which do not adequately account for the formation timescales of H2SO4and S8 clouds [8]. All of these factors result in major uncertainties in the magnitude and duration of any warming or cooling on early Mars.

We therefore wish to investigate, using a 3-D Global Climate Model (GCM), how cycles of emission, reaction, condensation and deposition of sulphur would have affected the radiative balance of Mars, and hence the timescales of any volcanically-induced warming and cooling cycles that took place on Mars. In particular, we wish to observe whether the finite timescales of formation of H2SO4 and S clouds were significant enough to allow for a short period of time just following a volcanic eruption in which SO2 and H2S greenhouse warming could dominate over atmospheric cooling from H2SO4 and S clouds.

Method:  We present the first implementation of the sulphur cycle on early Mars in a 3-D Global Climate Model (the Generic Planetary Climate Model (PCM) [9]) that takes a number of processes, most notably atmospheric chemistry, into account as shown in Figure 1. We simulate volcanic emission of sulphur according to a point surface flux of SO2, H2S, S2, HCl, CO and H2 as per the thermodynamic constraints on silicate partitioning in the Martian mantle [2], with a more reducing mantle favouring emission of H2S and S2, and a more oxidising mantle favouring SO2. Assuming a background atmosphere of 95% carbon dioxide and variable water vapour [4], we then simulate atmospheric chemistry according to 270 reactions that take odd-hydrogen, sulphur, nitrogen and chlorine chemistry into account [6,10-12], with the end products being H2SO4 (favoured in an oxidising atmosphere) and S­8 (favoured in a reducing atmosphere). These two molecules then condense out of the atmosphere and are deposited onto the ground.

Although H2SO4 and H­2O are expected to condense out together, a complex microphysical model involving binary H­2SO4-H2O condensation is difficult to implement due to the lack of knowledge of the density of cloud condensation nuclei in the early Martian atmosphere, as well as the lack of laboratory constraints on microphysical parameters at the low atmospheric temperatures predicted for early Mars. We therefore assume a constant cloud particle radius and ratio of H2SO4 to H2O, and model condensation according to diffusion-limited growth [13] in order to allow for supersaturation of H2SO4 in the atmosphere and thereby delay the onset of the anti-greenhouse effect of H2SO4 clouds as much as possible.  

Figure 1. (top) a diagram of the major processes included in our model of the sulphur cycle, (bottom) the major photochemical pathways involved in the production of S8 and H2SO4 from outgassed SO2, H2S and S2 based on the redox state of the atmosphere.

Results: We confirm the results of [7,8] and find that the amount of greenhouse warming induced by volcanic SO2and H2S emission is both too weak and too short to melt liquid water on the surface of Mars. Although the anti-greenhouse effect from H2SO4 and S8 cloud formation can be delayed by increasing the atmospheric pressure, the increased thermal inertia of the atmosphere also delays the greenhouse effect from SO2 and H2S (Figure 2). A particularly large eruption can even induce runaway cooling of the atmosphere, eventually leading to atmospheric collapse as CO2 is no longer stable in the atmosphere in its gaseous form. We are unable to mitigate this either by changing the oxygen fugacity and water content of the Martian mantle, or the microphysical properties of the binary H2SO4-H2O condensate cloud particles.

Figure 2. Simulation of a volcanic outgassing event (at the green cross) starting from three different average surface pressures, (top) surface temperature 7 days after the event and (bottom) increase in temperature relative to scenario where no eruption took place.

Acknowledgments: This work was carried out at the Jet Propulsion Laboratory California Institute of Technology under a contract with NASA. We recognize support for this project from NASA grant  20-SSW20-0086.

References: [1] Rapin, W. et al. (2023) Nature, 620, 299-302. [2] Gaillard, F. et al. (2013) Space Sci. Rev., 174, 251-300. [3] Forget, F. et al. (2013) Icarus, 222, 81-99. [4] Wordsworth, R. et al. (2015) J. Geophys. Res. Plan., 120, 1201-1219. [5] Yung, Y. L. et al. (1997) Icarus, 130, 222-224. [6] Johnson, S. S. et al. (2009) J. Geophys. Res. Plan., 114, E11011. [7] Tian, F. et al. (2010) EPSL, 295, 412-418. [8] Kerber, L. et al. (2015) Icarus, 261, 133-148 [9] Forget, F. et al. (1999) J. Geophys. Res., 104, 24155-24176. [10] Catling, D. C. et al. (2010) J. Geophys. Res., 115, E00E11. [11] Sholes, S. F. et al. (2017). [12] Stolzenbach, A. et al. (2023) Icarus, 395, 115447. [13] Hu, R. et al. (2012) ApJ, 761, 166.

How to cite: Braude, A., Kerber, L., Lefèvre, F., Jaziri, Y., Hamid, S., Maurice, M., Lefèvre, M., Millour, E., and Forget, F.: Modelling the Effect of the Sulphur Cycle on Episodic Climactic Changes on Early Mars, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-135, https://doi.org/10.5194/epsc2024-135, 2024.

On-site presentation
Kaito Koizumi, Hiromu Nakagawa, Kyoko K. Tanaka, Hitoshi Fijiwara, Takuo Tsuda, Yuki Kimura, Shohei Aoki, Naoki Terada, Yasumasa Kasaba, Ann Carine Vandaele, Ian Thomas, Bojan Ristic, Frank Daerden, Zachary Flimon, Yannick Willame, Jonathon P. Mason, Manish R. Patel, Giuliano Liuzzi, Giancarlo Bellucci, and José Juan López-Moreno

In the mesosphere on Earth, water ice clouds are frequently observed in the low-temperature region (below -130℃) at altitudes 80-90 km in the polar region. Two mechanisms have been proposed to explain the formation of these ice particles. One is homogeneous nucleation, in which condensation nuclei are formed from water vapour. The other is heterogeneous nucleation, in which substrates such as aerosol in the atmosphere undergo a phase change as nuclei. The latest theoretical study shows that heterogeneous nucleation is predominant in the nucleation of mesospheric clouds on Earth and that homogeneous nucleation is unlikely to occur, when compared to observed conditions (Tanaka et al., 2022; https://doi.org/10.5194/acp-22-5639-2022). This theory may apply to cloud formation in other planetary atmospheres. On Mars, mesospheric clouds like those on Earth have been observed, but there are still many unresolved issues. In particular, the nucleation has only been studied theoretically by applying a classical theory for the lower atmospheric clouds (Määttänen et al., 2005). The purpose of this study is to clarify the nucleation mechanism of the Martian mesospheric clouds by comparing the mesospheric cloud observations obtained at Mars with theory of Tanaka et al. (2022).

We used the solar occultation spectral data obtained by the ultraviolet (UV) to visible (VIS) channel UVIS of the Nadir and Occultation for MArs Discovery (NOMAD) spectrometer on board the ExoMars Trace Gas Orbiter (TGO) to clarify the purpose. The observational data considered this study consist in 9249 atmospheric transmission profiles covering the period from Ls (areocentric longitude of the sun) = 163°in MY (Martian Year) 34 to Ls = 218°in MY 36 (2018/4/22-2022/4/30) (Figure 1). In this study, we derive the total optical depth along the line of sight (slant opacity) from the transmittance spectra (Streeter et al., 2021). We attempt to distinguish between water ice clouds and dust by comparing the slant opacity at 320 nm, where we assume a large contribution from water ice clouds, with the slant opacity of all aerosols, including dust, at 600 nm. The existence of water ice clouds is determined under the conditions that the optical thickness at 320 nm is larger than 0.01 at altitudes of 40-100 km and the slant opacity ratio (320 nm / 600 nm) is larger than 1.5. The atmospheric density, dust density, atmospheric temperature and cooling rate, dust particle size, and water vapour pressure of the atmospheric conditions are estimated from the Mars Climate Database (MCD) (version 5.3; Millour et al., 2012), a numerical atmospheric general circulation model, and applied to the theory of Tanaka et al. (2022) to investigate the possibility of homogeneous and heterogeneous nucleation.

Following the thresholds described above, Martian mesospheric water ice clouds were detected in 966 out of 9249 altitude distributions (152 in MY 34, 615 in MY 35, and 199 in MY 36). In addition, the relationship between clouds and the background atmospheric field was investigated, and it was clear that clouds tend to form under atmospheric conditions where the water vapor pressure is above 10-5 Pa and the temperature is below 200 K (Figure 2). Out of the 966 data, data were selected by saturated vapour pressure corresponding to every 10 K in the range of 130 K to 180 K. These were compared with the conditions obtained by Tanaka et al. (2022) for whether homogeneous or heterogenous nucleation predominates (Figure 3). The results suggested that when the background atmospheric water vapour pressure is above 1.56-5 Pa (saturated water vapour pressure at 150 K) at the time of cloud formation, the Martian atmosphere can only have atmospheric conditions where heterogeneous nucleation occurs, as on Earth. This result clarified that heterogeneous nucleation is predominant in the nucleation of mesospheric water ice clouds on Mars. On the other hand, when the water vapour pressure is less than 9.40-7 Pa (saturated water vapour pressure at 140 K), it was indicated that the Martian atmosphere can have atmospheric conditions that produce homogeneous nucleation. In fact, some of the clouds detected at altitudes above 70 km below the saturated water vapour pressure of 140 K suggested the possibilities of homogeneous nucleation. The latter is unexpected because it is a Mars-specific event that cannot occur on Earth. Detailed analysis of the dust density and dust particle size using the results derived from the instrument's observation data is needed in the future, to clarify the atmospheric conditions under which homogeneous nucleation can occur, which is not seen on Earth but is suggested on Mars.


How to cite: Koizumi, K., Nakagawa, H., K. Tanaka, K., Fijiwara, H., Tsuda, T., Kimura, Y., Aoki, S., Terada, N., Kasaba, Y., Vandaele, A. C., Thomas, I., Ristic, B., Daerden, F., Flimon, Z., Willame, Y., P. Mason, J., R. Patel, M., Liuzzi, G., Bellucci, G., and López-Moreno, J. J.: Nucleation mechanism of mesospheric water ice clouds on Mars observed by TGO/NOMAD, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-718, https://doi.org/10.5194/epsc2024-718, 2024.

On-site presentation
Michal Steiner

Over 5500 exoplanets have been discovered, predominantly through transits on short orbits. Notably, hot Jupiters and the absence of Neptune-sized planets (Neptune desert) have been identified, thanks to missions like Kepler. These types of planets can be very different in density, mainly due to the radius-inflation effect, whose origin is unclear. This, in particular, changes the atmospheric properties and chemical composition, which can be extracted through transmission spectroscopy at both low and high resolution. Furthermore, at high resolution, we can also observe the Rossiter-McLaughlin effect, providing us with the projected spin-orbit angle, an excellent probe into the dynamical history of the system. We will show the results of high-resolution transmission spectroscopy and the Rossiter-McLaughlin effect of WASP-31 b, a Jupiter-sized planet, using the ESPRESSO spectrograph. 


This planet has already been studied by a plethora of instruments. In particular, Sing+2016 found, using HST/STIS, an extremely strong signature of potassium. However, Gibson+2017 and later Gibson+2019, using VLT/FORS2 and VLT/UVES respectively, contradicted this signature. Furthermore, Flagg+2023 and later Flagg+2024 found CrH for the first time in an exoplanet's atmosphere. Brown+2017 analyzed the Rossiter-McLaughlin signature of this planet, which shows WASP-31b to be aligned (projected obliquity, λ). 


In this analysis, we focused on the species sodium (Na), potassium (K), and iron (Fe). We also used the CrH template, although it is weaker in the wavelength range of ESPRESSO.

How to cite: Steiner, M.: High-resolution spectroscopy of WASP-31b with ESPRESSO, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-307, https://doi.org/10.5194/epsc2024-307, 2024.

On-site presentation
Clàudia Soriano Guerrero


Hot Jupiters (HJs) are gas giants orbiting very close to their host stars, with orbital periods of a few days, corresponding to distances within about 0.1 AU. Due to the high irradiation from their host stars and the tidal locking of the rotational and orbital periods, strong temperature differences persist between the dayside and the nightside. This triggers strong thermal zonal jets that tend to redistribute the heat, as shown in global circulation models (GCMs).
Most HJs have inflated radii, up to double of what cooling models for planetary evolution predict. A strong correlation with the irradiation is observed, with inflation starting to appear for equilibrium temperatures above about Teq = 1000 K. However, the effects of irradiation alone are not quantitatively sufficient to explain the large radii inflation, given the shallowness of the absorbing layer of the radiation. Therefore, the most probable explanation is the continuous deposition of some additional heat.
Among the possible physical mechanisms, one of the most popular is Ohmic heating due to the dissipation of currents induced by the magnetic field which is produced by the zonal winds composed of ionized material. The Ohmic mechanism fits the inferred efficiency trend above: as the irradiation increases, the conductivity and the induced currents increase monotonically, until the generated magnetic fields are strong enough to slow down the global zonal winds via magnetic drag, thus self-regulating the system and limiting the overall efficiency of the mechanism

Most existing studies considered semi-analytical estimates within the linear regime of the induction, i.e. when the atmospheric dynamics produces a small perturbation over the background magnetic field generated in the interior. This approach is valid for relatively low conductivities, corresponding to temperatures T < 1500 K. For higher temperatures, the induced magnetic field is locally so high that the linear approximation fails. Our project focuses on simulations that can connect both regimes.


As a first step, in our first work we focused on the non-linear regime, i.e. when the induced magnetic fields are comparable or larger than the internal ones. We presented local ideal MHD simulations of a narrow atmospheric column in the dayside radiative layers of a HJ upper atmosphere (1 mbar-10 bar), which can be seen as an extension of the earlier non-magnetic studies. We included realistic, parametrized profiles for the wind velocity, mimicking the steepest profiles of GCMs and turbulent perturbations. We found that, under conditions that are typical of ultra hot Jupiters (T > 3000 K), a strong toroidal field (of the order of several hundred gauss) is created in the shear layer, confined by meridional currents. Moreover, turbulent small-scale structures induce further currents in deeper regions, but more detailed simulations were needed to assess this clearly.

In this second work, we go a step further to quantify such dissipation, we study the combined effect of winding and atmospheric turbulence. We use realistic profiles for the wind velocity and pressure, obtained from GCM simulations, for different exoplanets. We also include realistic conductivity, which depends on temperature and pressure and can be approximated by classical formulae for the potassium contribution, dominant for the typical HJ. We consider the modelling of four concrete exoplanets, as an application: two moderately irradiated (HD209458b, HD189733b), and two highly irradiated (WASP18b, WASP121b).


In our simulations we observed modifications to the profiles and intensities of magnetic fields and currents, compared to both the ideal MHD scenario and the linear regime, especially for intermediate T of about 1500-2000 K, where the bulk of observed HJs lies, due to the winding effect. Such profiles change within the same planet, having a more extreme profiles (in terms of shear of the zonal wind) close to the substellar point, and being more mild at different latitudes and longitudes.

On the other hand, 1D simulations give us information about the winding effect and the amplification of the magnetic field as seen before, however full 3D simulations are very important, since they provide us with information about the amount of currents that can eventually penetrate the convective region below the radiative-convective boundary (RCB) for different cases due to perturbations. These simulations have found that the extremely strong electrical currents generated can be sufficient to account for the observed inflation of HJs' radii, provided these currents reach the inner layers. Furthermore, magnetic fields in the hottest planets can reach up to kilogauss levels locally around shear layers, with significant variability in induced currents influenced by local planetary temperatures. This work lays the groundwork for future studies on the radio detectability of these features.

How to cite: Soriano Guerrero, C.: Magnetic winding and turbulence in hot Jupiters, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-225, https://doi.org/10.5194/epsc2024-225, 2024.

On-site presentation
Alexandra Lehtmets, Mihkel Kama, Anna Aret, and Luca Fossati

In our study, we investigate how early-type stars influence the gases escaping from exoplanet atmospheres into space. We focus on two key aspects: how the star's radiation force and gravity affect the path of these gases, and how fast neutral atoms speed up before changing into ions. By combining theories and models, we aim to understand these processes better. Our research not only deepens our understanding of exoplanets but also sheds light on their relationship with the stars they orbit. Additionally, our models could help predict which chemical elements end up accreting on to the host star. For early-type stars, our predictions might even show up as observable patterns in their spectra, because one of the unique features of early-type stars is that material accreting onto them can easily “pollute” the photosphere. 


How to cite: Lehtmets, A., Kama, M., Aret, A., and Fossati, L.: Evaporated atmosphere in the interplanetary medium of early-type stars, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-33, https://doi.org/10.5194/epsc2024-33, 2024.

On-site presentation
Philipp Baumeister, Nicola Tosi, Caroline Brachmann, John Lee Grenfell, and Lena Noack

The James Webb Space Telescope has ushered in the age of exoplanet atmosphere characterization. Not only is it possible for the first time to detect atmospheres on rocky exoplanets, the spectral analysis of the atmosphere allows a compositional characterization of the major gas species. This holds the promise of gaining insight into the interiors of exoplanets and their mineralogical make-up, which are otherwise hidden from view.

The atmosphere and interior of a rocky planet do not form separate systems, but are coupled by an intricate network of feedback processes which link the evolution of the atmosphere to the evolution of the interior, and vice-versa. In particular, volcanic outgassing of volatile species from the planet’s silicate mantle shapes the atmospheric composition, temperature, and pressure, but the exact composition of outgassed species not only depends on the volatile content and oxidation state of the mantle, but also on the current state - i.e., pressure, composition, and temperature - of the atmosphere. In particular, many feedback loops rely on (or are influenced) by the presence of water: The climate-stabilizing carbonate-silicate cycle depends on an active water cycle for the weathering of silicates, i.e. surface temperatures which permit liquid water. The presence of liquid water is a necessary precondition for the development of life. Water in the form of hydrous minerals significantly influences the convection dynamics of the mantle by lowering the viscosity and melting point of rocks, promoting more vigorous convection and volcanic activity, which in turn drives the atmospheric evolution. An understanding of the interplay of these processes is necessary to interpret observed exoplanet atmospheres and to quantify the necessary planetary properties which lead to the emergence of habitable conditions. 

Here, we explore the diversity of atmospheres that may emerge on stagnant-lid exoplanets — those without plate tectonics — and identify the parameters which lead to the emergence of habitable conditions. Our investigation includes various key parameters, such as planet mass, the size of the iron core, the oxidation state and water content of the mantle, as well as the distance of the planet to its host star. We use a 1D numerical model to simulate the coupled evolution of the interior and atmosphere. We include a comprehensive array of feedback processes and interactions between interior and atmosphere, such as a CO2 weathering cycle, volcanic outgassing, a water cycle between ocean and atmosphere, greenhouse heating, as well as escape processes of H2. While many atmosphere-interior feedback processes have been studied before in detail, we present here a comprehensive model combining the important planetary processes across a wide range of terrestrial planets.

The modeling of more than 280 000 coupled atmosphere-interior evolutions shows that a wide diversity of atmospheric compositions develops in response to interior properties, in particular driven by the oxidation state of the mantle and its water content. Only a narrow range of mantle oxidation states allows long-term habitable conditions, and many planets with oxidized mantles end up with Venus-like hot, dense atmospheres instead. On the other hand, on planets with more reducing mantles, the amount of outgassed greenhouse gasses is often too low to keep the surface above the freezing point of water.

How to cite: Baumeister, P., Tosi, N., Brachmann, C., Grenfell, J. L., and Noack, L.: Redox state and interior structure control on the long-term habitability of stagnant-lid planets, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-425, https://doi.org/10.5194/epsc2024-425, 2024.


Posters: Tue, 10 Sep, 10:30–12:00

Display time: Tue, 10 Sep 08:30–Tue, 10 Sep 19:00
On-site presentation
Hiroto Mitani

The intense extreme ultraviolet radiation heats the upper atmosphere of close-in exoplanets and drives the atmospheric escape through photoionization of hydrogen atoms. The intense atmospheric escape is a key process to understand the evolution of close-in exoplanets. The mass loss rate depends on the planetary environment and parameters (e.g. UV flux at the planet, planetary radius, mass).

The escape process can be characterized by the gravity, photoheating/cooling, and gas expansion. We introduce the relevant physical quantities which describe the dominant physics in the atmosphere. Particularly the introduction of a characteristic temperature describing how much the atmosphere is heated by photoionization can be used to understand physical quantities of atmospheric escape, including the mass-loss rate. We find that the equilibrium temperature for phootoionization of hydrogen and the characteristic temperature determine whether the system becomes energy-limited or recombination-limited. The atmospheric temperature can be given by these temperatures.

We derive an analytic formulae for mass-loss rate and efficiency driven by EUV photoinization which can explain the results from 1D hydrodynamic simulations. We also classify close-in exoplanets with Ly-a, Ha, and Helium triplet observations which reflects the thermo-chemical structure of the upper atmosphere. Our classification suggests the future candidate to observe absorption by the upper atmosphere with longer photoionization timescale and larger mass-loss rates.

How to cite: Mitani, H.: Theoretical undestanding of atmospheric escape of close-in planets driven by EUV photoionization, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-198, https://doi.org/10.5194/epsc2024-198, 2024.

On-site presentation
Alexandre Gillet

Planetary mass-loss is governed by several physical mechanisms such as: thermal hydrodynamic escape, photochemical escape, ionospheric outflow, interaction with the stellar wind and dynamical events such as flares. All these processes affect the model-estimated atmospheric mass loss rates. The phenomenon of hydrodynamic escape has long been postulated to have acted upon Earth, Venus and Mars in their early lives. The ongoing detection and characterisation of exoplanets offers a new window into the underlying physics. With this new insight, we expect to offer new clues into the formation of planets near and afar. Moreover, the stellar radiation energy deposited as heat depends strongly on the energy of the primary electrons following photoionisation and on the local fractional ionisation. We perform 1D spherical and 2D Cartesian HD simulations with the PLUTO code of an atomic hydrogen planetary atmosphere. We assess the impact of the shape of different XUV spectra taken from the MUSCLES survey of type K and M type stars on the mass loss rate and the impact of flare events on the planetary atmosphere. For the first time, we take into account the effect of secondary ionisation by photoelectrons self-consistently in different Exosystems. In our explored sample, we also vary the planetary masses and report a significant diminution up to 54% of the planetary mass loss rate for a planet with a mass of 0.02 Mj.

How to cite: Gillet, A.: Influence of secondary ionisation by photoelectrons on exoplanetary atmospheres, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-486, https://doi.org/10.5194/epsc2024-486, 2024.

On-site presentation
zachary flimon, Justin Erwin, Severine Robert, Lori Neary, Arianna Piccialli, Loic Trompet, Yannick Willame, Frank Daerden, Sophie Bauduin, Michael Wolff, Ian Thomas, Bojan Ristic, Giancarlo Bellucci, Manish Patel, Cedric Depiesse, Ann-Carine Vandaele, Jon P Mason, José juan Lopez-Moreno, and Filip Vanhellemont

Aerosols are an important part of the Martian atmosphere. They are composed of dust, H2O ice, and CO2 ice. Dust is the main aerosol and has a significant contribution to the radiative transfer budget, as it absorbs solar radiation, leading to local heating of the atmosphere. Dust is confined to lower altitudes during the aphelion season and can reach higher altitudes during the perihelion, especially during dust storms that frequently arise on Mars during this period. The seasonal behavior of the dust will lead to temperature variations in the atmosphere that are important, especially for modelers. Ice clouds are more present during the aphelion when the temperature is colder and follow a seasonal pattern. Different types of clouds can be found throughout the year and contrary to dust, they reflect sunlight and locally cool the atmosphere.

The thermal and dynamical structure of the atmosphere, as well as the distribution of chemical species are sensitive to the aerosol’s abundance and size.

The NOMAD (“Nadir and Occultation for MArs Discovery”) spectrometer suite onboard the ExoMars Trace Gas Orbiter (TGO) is composed of three spectrometers. In this work, we will use the UVIS and SO channels in occultation mode. Both channels are respectively in the UV-Visible (200-650 nm) and infrared (2.3-4.3 µm).

We first developed a methodology to compute extinction and particle sizes with the UVIS channel. The climatology produced allowed us to study aerosols along different seasons and latitudes between the second half of Martian Year (MY) 34 up to the end of MY 36 (figure 1).

Using only the spectral range of UVIS in occultation, dust, H2O ice, and CO2 ice cannot be differentiated because the three aerosols have similar extinction features. To model the extinction cross-section, we assume spherical symmetry and use a Mie scattering code (Bohren, et al., 1998). We use the commonly used log-normal size distribution with the parameterization of (Hansen, et al., 1974).

We show that with UVIS it is possible to distinguish size between 0.1 to 0.8 µm with confidence. When the particles are larger, it is not possible to retrieve the precise size, as the spectra does not possess any absorption bands.

With the addition of the infrared channel, NOMAD SO, we can broaden the sensitivity with respect to particle size and can retrieve the composition of the aerosols. H2O ice, CO2 ice, and dust possess different signatures in the IR (figure 2) and it is possible to differentiate them with confidence. The combination of both UVIS and SO greatly improves the retrieval of particle size as it allows us to have more sensitivity for larger particles.

Several works have already published climatologies of aerosols with NOMAD.   Liuzzi et al., (2019) study water ice cloud and dust particles with the SO channel during MY34 and the beginning of Martian year 35.They were able to discriminate the aerosols and study the presence and evolution of water ice clouds during dust storms. Stolzenbach et al., (2023) also made a similar study , also using SO,  from MY 34 to MY 35. Both works were able to study in detail the size distribution during dust events.

Streeter et al (2022), used the UVIS channel to produce a climatology of aerosols between MY34 to the end of MY35. They derived extinction vertical profiles but not the size of the particles. Using a model, they were also able to study the presence of water ice clouds and dust in the atmosphere.

By the combination of previous work’s results, and the methodology developed for the UVIS channel, we aim to create a new climatology covering from MY34 to the end of MY 36. This new data set will use information contained in the UV and IR channels allowing us to have greater constraints on size and composition of the aerosols. We will be able to study in detail the evolution and occurrence of detached layers during several seasons and latitudes.


Figure 1: Extinction vertical profiles with the UVIS channel as a function of LS for the northern ([30°,70°] Lat, Top panel), equatorial ([-30°,30°] Lat, Middle panel), and southern latitude ([-70°,-30°] Lat, Bottom panel) regions for Martian Years 34, 35, and 36. The extinction is taken as the average between 320 and 360 nm. Shaded regions denote periods where there are no observations due to orbital geometry, while the white regions are where the spectrum is rejected. Both sunset and sunrise occultations are averaged in this figure.

Figure 2: Example of SO extinction spectra (in red) showing the absorption due to water ice (in orange) with other aerosols here for comparison.

How to cite: flimon, Z., Erwin, J., Robert, S., Neary, L., Piccialli, A., Trompet, L., Willame, Y., Daerden, F., Bauduin, S., Wolff, M., Thomas, I., Ristic, B., Bellucci, G., Patel, M., Depiesse, C., Vandaele, A.-C., Mason, J. P., Lopez-Moreno, J. J., and Vanhellemont, F.: Aerosol Climatology on Mars as Observed by NOMAD UVIS/SO on ExoMars TGO, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1014, https://doi.org/10.5194/epsc2024-1014, 2024.

On-site presentation
Jeanna Buldyreva

The advent of new-generation space missions (such as WFIRST and ARIEL) as well as high-performance observatories both space-born and ground-based (such as JWST and ELTs) should start to answer fundamental questions about the formation, composition and properties of exoplanets. A reliable interpretation of the observations will rely on a huge amount of spectroscopic data, with a particular emphasis on high-resolution spectroscopic data.

Because of the extreme conditions characteristic of exoplanetary atmospheres (high temperatures and high levels of insolation), much information on molecular processes and their spectroscopic signatures is not available. In particular, lack of adequate procedures to measure or calculate collisional line-shape parameters for billions of transitions required limits severely the quality of the atmospheric modelling and retrievals. Line-shape profiles and pressure-broadening coefficients for “exotic” molecular species constitute a basis for cross-sections calculations which are further used to calculate atmospheric opacities. It was shown recently [1] that account of pressure-broadening effect on the spectral line shapes is essential to enhance our capacity for studying exoplanets. Several spectroscopic databases, such as HITRAN [2], GEISA [3], ExoMol [4], TheoReTS [5] and MoLList [6]) provide extensive line lists of positions and intensities of isolated spectral transitions, some of which contain many billions of lines.  However, the associated pressure-broadening and shift parameters, as well as their temperature dependences, remain poorly determined or completely missing. Therefore, there is a huge demand for robust theoretical approaches and estimates that could provide line-shape parameters for a large range of excitations covering wide ranges of temperatures and pressures and large variety of perturbers.

First steps in this direction have been made recently with developing at least approximate theoretical approaches [7] to getting pressure-broadening parameters for most infrared-active molecules detected or expected in exoplanetary atmospheres. Rotationally independent estimates of pressure-broadening coefficients have been generated for more than 50 active species (see Table) and 12 perturbers (Ar, CH4, CO, CO2, H2, H2O, He, N2, NH3, NO, O2 and self). Full data sets have been put in a specifically designed for this purpose prototype database COLLINE [8] for testing, and one-value data have been selected for each molecular pair for including in the 2024 release [4] of ExoMol.

Table: Exomolecules with new line-broadening coefficients.

























































In this work, we describe the main features of newly produced line-broadening data, their organization in the COLLINE database and selection of some of them for including in ExoMol. We provide also some examples showing the influence of different pertubers on the cross-sections calculated for active molecules. Ways to further populating of databases for exoplanetary molecules will be outlined.



[1] J.J. Fortney, T.D. Robinson, S. Domagal-Goldman et al., arXiv:1905.07064 (2019)

[2] I.E. Gordon, L.S. Rothman, R.J. Hargreaves et al., J. Quant. Spectrosc. Radiat. Transfer 277, 107949 (2022)

[3] N. Jacquinet-Husson et al., J. Mol. Spectrosc. 327, 31 (2016)

[4] J. Tennyson, S.N. Yurchenko, J. Zhang et al., J. Quant. Spectrosc. Radiat. Transfer, under revision (2024)

[5] A.V. Nikitin, Y.L. Babikov, V. G. Tyuterev, J. Mol. Spectrosc. 327, 138 (2016)

[6] P.F. Bernath, J. Quant. Spectrosc. Radiat. Transfer 240, 106687 (2020)

[7] J. Buldyreva, S.N. Yurchenko, J. Tennyson, RASTI 1, 43 (2022)

[8] COLLINE database: https://colline.u-bourgogne.fr

How to cite: Buldyreva, J.: Influence of molecular collisions on the atmospheric modelling: new data and updates in spectroscopic databases, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1084, https://doi.org/10.5194/epsc2024-1084, 2024.

On-site presentation
Caroline Brachmann, Lena Noack, Frank Sohl, and Fabrice Gaillard

Rocky exoplanets' internal constitution is inferred indirectly through their atmospheric composition. Confidence in this inference necessitates coupling interior and atmospheric models. In the past, various atmospheric redistribution models were developed to determine the composition of exoplanetary atmospheres by varying element abundance, temperature and pressure (Woitke et al., 2021).

However, these models neglect that present-day atmospheres were formed via volcanic degassing and, consequently, element abundances are limited by thermodynamic processes accompanying magma ascent and volatile release. Here we combine volcanic outgassing with an atmospheric chemistry model to simulate the evolution of C-H-O-N-S atmospheres in thermal equilibrium below 600 K. These volatiles can be stored in significant amounts in basaltic magmas and are the most commonly degassed species.

Our model calculates possible atmospheric compositions by varying oxygen fugacity, melt and surface temperature, and volatile abundances, considering phase solubility, atmospheric processes (e.g., water condensation, hydrogen escape), the change in redox conditions caused by volcanic activity and the influence of existing atmospheres on further degassing.

Our findings indicate that the prevailing atmospheric type below 600 K typically consists of CO2, N2, CH4, and, depending on temperature, H2O. Moreover, we illustrate that evolving atmospheric pressure and composition hinge significantly on the oxygen fugacity of the melt due to its impact on gas speciation and solubility. Reduced conditions yield atmospheres dominated by H2, NH3, CH4, and H2O, with exceedingly low atmospheric pressures. In contrast, oxidized conditions result in atmospheres comprising H2O, CO2, N2, and limited CH4, accompanied by high atmospheric pressures. Sulfur gases emerge predominantly at higher surface temperatures, manifesting as S2 or H2S under low mantle redox states and as SO2 under high mantle redox states. Notably, O2 is not generated abiotically, as sufficient carbon or hydrogen remains available to form H2O, CO, or CO2. Therefore, the formation of O2-dominated atmospheres would require excessive photodissociation of H2O or CO2 (Chang et al., 2021), a phenomenon likely common on planets orbiting M-dwarf stars.

In addition to highlighting the indirect inference of rocky exoplanets' internal constitution through their atmospheric composition, we demonstrate that reduced magmas can oxidize via H2 and CO degassing, whereas oxidized magmas may undergo reduction through SO2 degassing. Furthermore, we conclude that the depth of the magma source region and the planetary size significantly influence atmospheric compositions due to the varying pressure dependence of degassed species' solubilities.

How to cite: Brachmann, C., Noack, L., Sohl, F., and Gaillard, F.: Atmospheric compositional variations due to changes in mantle redox state , Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-209, https://doi.org/10.5194/epsc2024-209, 2024.