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.

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_8­ 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_8­ 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.

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.

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.

INTRODUCTION

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.

OHMIC DISSIPATION STUDY

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).

RESULTS AND CONCLUSIONS

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.

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.

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.