Decyphering the chemical composition and atmospheric conditions of terrestrial planets around other stars is one of the main driver of exoplanetary science. In fact, atmospheric characterisation of Earth-like planets is expected to bring the first insights into the possibility of biological activity on another planet than Earth. Although the road to the detection of such potential biomarkers is long and challenging, recent spectacular progress have been achieved about the composition, climates and evolution of giant exoplanets with new instruments in space (with the James Webb Space Telescope or the Characterising Exoplanets Satellite) and on the ground (with high-resolution spectrographs at giant telescopes). Today, future projects are being designed to bridge the gap between hot gas giants and temperate terrestrial planets and take us closer and closer to this scientific goal. In this talk, I will review the current challenges and exciting perspectives about the atmospheric characterisation of terrestrial exoplanets.

How to cite: Ehrenreich, D.: Challenges and perspectives for the characterisation of the atmospheres and exospheres of 'terrestrial’ exoplanets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7647, https://doi.org/10.5194/egusphere-egu23-7647, 2023.

We investigate the past evolution of the climate of Earth and Earth-like planets as a coupled interior/atmosphere system. We compare climatic states obtained through parameterized modelling versus a physics-based 3D General Circulation Model (GCM). Finally, we identify characteristics in the 3D simulations that most affect the climate, and how that impacts the reliability of parameterized modeling.

In long-term planetary evolution studies, surface conditions are often characterized using global average temperatures, and calculated using simple models (i.e., Eddington approximation, 1D radiative convective gray atmosphere). For instance, these models treat albedo and cloud cover in a parameterized way and are not always able to assess local variations (i.e., latitudinal). A more self-consistent approach uses a 3D GCM, which requires extensive computing resources and time. This makes GCMs unpractical for long-term evolution modelling. Instead, here, successive windows into the past states of the atmosphere/surface are modeled.

The past thermal history of Earth’s interior is used as a representative case for a range of possible past states and evolution of the mantles of Earth-like exoplanets. This feeds a parameterized model for mantle thermal and dynamic evolution. From the computation of melt generation and volcanism, the volatile delivery from the mantle into the atmosphere is estimated. This produces a variety of atmospheric composition evolutionary pathways, which, in turn, govern planetary climate evolution.

We use the ROCKE3D GCM during significant windows of the long-term evolution to understand the differences between the parameterized (coupled evolution) and more complete (GCM) approaches. We compare average surface temperatures and albedos obtained in both simulations. We then evaluate the ice coverage obtained in GCM simulations and compare it to the usual criteria for habitability (such as average temperatures above 273-258 K). Finally, we assess the reasons for discrepancies between the models.

In particular, we study the influence of the total atmosphere pressure, and its composition (N₂, CO₂, O₂, CH₄), consistently with Earth observation, as well as solar insolation and length of day variation, depending on the different eras we consider. We further study the impact of continental distribution (i.e., present-day-like or supercontinent distributions) and topography. We use the mantle dynamics simulation output based on the thermal history to assess the characteristics of the surface features. The trend of the variations of average temperature through time (and CO₂ abundances) is consistent in parameterized vs. GCM models. Perturbation around the reference model result in stronger temperature variations in the GCM due to albedo feedback. Indeed the albedo variations can be significant in 3D simulations and are not considered in the parameterized approach. Supercontinent setups result in markedly dryer land than present-day Earth. Even models with average temperatures below 273-268 K have significant ice-free ground in all continental setups.

How to cite: Gillmann, C., Seales, J., Hassanzadeh, P., and Lenardic, A.: The Climate of Earth and Earth-like (Exo)planets in Coupled Evolution Models: Insights from 3D GCM., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2829, https://doi.org/10.5194/egusphere-egu23-2829, 2023.

Previous studies have found that high-energy radiation like cosmic rays and stellar energetic particles, can induce the initial nucleation of cloud particles from molecular clusters, but the effect on larger existing particles is still poorly understood.

This study explores the question “How is the aggregation of mineral cloud particles affected by high-energy radiation and humidity?”. We present experiments conducted in an atmosphere chamber on the charging and aggregation of 50nm SiO₂ particles under varying degrees of gamma radiation and relative humidity. 
We observe an aggregation of the SiO₂ particles to form larger clusters, and that this aggregation is inhibited by irradiation with gamma radiation. We find that non-irradiation SiO₂ particles are generally more positively charged in comparison to a bipolar charge distribution, and that gamma radiation shifts the particles to a more negative charge. The effect of gamma radiation on the aggregation and charge of the particles is present both at lower (~20%) and higher (~60%) relative humidity. When varying the relative humidity from ~20% to ~80% we find no significant direct effect of relative humidity on the aggregation of the particles. These results are presented and discussed in relation to previous studies of nucleation and condensation.

In recent years, exoplanet research has focused on how we can interpret atmosphere observations through models, and here cloud formation has proven to be a challenge. Clouds are known to play a role in both the energy balance and chemistry of atmospheres, as well as directly affecting the spectrum observed from a planet. Exoplanet clouds are believed to be very chemically heterogeneous and SiO₂ is one of the species that easily condense, making SiO₂ relevant both as a nucleation seed on Earth-like planets and as a cloud species on Exoplanets. Since cloud formation has been found to be affected not only by the atmospheric properties, but also by high-energy radiation from outside the atmosphere it indicates that the host star and interstellar environment of an exoplanet might affect its clouds.

How to cite: Bach-Møller, N., Helling, C., Gråe Jørgensen, U., and Bødker Enghoff, M.: Aggregation and charging of mineral cloud particles underhigh-energy irradiation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14084, https://doi.org/10.5194/egusphere-egu23-14084, 2023.

In this study, we employ a cloud-resolving model (CRM) to investigate how gravity influences convection and clouds in a small-domain (96 km by 96 km) radiative-convective equilibrium (RCE). Our experiments are performed with a horizontal grid spacing of 1 km, which can resolve large (> 1 km²) convective cells. We find that under a given stellar flux, sea surface temperature increases with decreasing gravity. This is because a lower-gravity planet has larger water vapor content and more clouds, resulting in a larger clear-sky greenhouse effect and a stronger cloud warming effect in the small domain. By increasing stellar flux under different gravity values, we find that the convection shifts from a quasi-steady state to an oscillatory state. In the oscillatory state, there are convection cycles with a period of several days, comprised of a short wet phase with intense surface precipitation and a dry phase with no surface precipitation. When convection shifts to the oscillatory state, water vapor content and high-level cloud fraction increase substantially, resulting in rapid warming. After the transition to the oscillatory state, the cloud net positive radiative effect decreases with increasing stellar flux, which indicates a stabilizing climate effect. In the quasi-steady state, the atmospheric absorption features of CO₂ are more detectable on lower-gravity planets because of their larger atmospheric heights. While in the oscillatory state, the high-level clouds mute almost all the absorption features, making the atmospheric components hard to be characterized.

How to cite: Liu, J., Yang, J., Zhang, Y., and Tan, Z.: Convection and Clouds under Different Planetary Gravities Simulated by a Small-domain Cloud-resolving Model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2306, https://doi.org/10.5194/egusphere-egu23-2306, 2023.

The history of water escape from Mars has been a topic of intense interest among the scientific community. Water escape from Mars is generally studied by measuring the escape rate of atomic hydrogen from its exosphere and tracing it back in time to determine the total amount lost by the planet. However, the loss rates are estimated assuming thermal properties for the H atoms, and are therefore a lower limit. Past analyses of spacecraft observations presented indirect evidence for the existence of an energetic non-thermal H population. However, all these observations lacked a clear detection. Here we present the first unambiguous observational signature of non-thermal H at Mars, consistent with solar wind charge exchange as the primary driver for its production. The calculated non-thermal H escape rates reach as high as ~26% of the thermal escape rate near aphelion. An active Sun today would increase the present-day escape rate of H and a younger energetic Sun likely contributed towards a significant loss of water from Mars, thereby shortening the martian water escape history timeline.

How to cite: Clarke, J., Bhattacharyya, D., Mayyasi, M., Shematovich, V., Bisikalo, D., Chaufray, J.-Y., Thiemann, E., Halekas, J., Schmidt, C., Bertaux, J.-L., Chaffin, M., and Schneider, N.: Evidence of Hot Hydrogen in the Exosphere of Mars Resulting in Enhanced Water Loss, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9581, https://doi.org/10.5194/egusphere-egu23-9581, 2023.

Analyzing extreme ultraviolet spectra of the Martian upper atmosphere obtained from the Hisaki space telescope, we found anti-correlation between hydrogen (HI Ly-β) and oxygen (OI 1356 Å and OI 1304 Å) airglow brightness during one of the major regional dust storms in Mars Year 33 (Masunaga et al., 2022). Ly-β brightness gradually increased by a factor of 2 over the observation period (L_S=213°–232°) while oxygen airglow temporarily decreased by a factor of 3 during the dust storm period. We also found that their brightness varied alternately with a periodicity of ~6–8 days. The magnitude of their periodic airglow variations was ~20–50% for the whole disk, and the periodicity was consistent with that of atmospheric waves observed by the Curiosity Rover on the surface of Mars. These results suggest that hydrogen and oxygen abundances in the Martian upper atmosphere are highly controlled by dust- and wave-couplings between the lower and upper atmosphere, possibly altering the efficiency of hydrogen and oxygen escape from Mars.

Reference

Masunaga, K., N. Terada, N. Yoshida, Y. Nakamura, T. Kuroda, K. Yoshioka, Y. Suzuki, H. Nakagawa, T. Kimura, F. Tsuchiya, G. Murakami, A. Yamazaki, T. Usui, and I. Yoshikawa, Alternate oscillations of Martian hydrogen and oxygen upper atmospheres during a major dust storm, Nature Communications, 13, 6609, 2022

How to cite: Masunaga, K., Terada, N., Yoshida, N., Nakamura, Y., Kuroda, T., Yoshioka, K., Suzuki, Y., Nakagawa, H., Kimura, T., Tsuchiya, F., Murakami, G., Yamazaki, A., Usui, T., and Yoshikawa, I.: Hisaki space telescope observations of the large oscillations of Martian hydrogen and oxygen upper atmospheres, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1968, https://doi.org/10.5194/egusphere-egu23-1968, 2023.

Observations of the sodium exosphere of Mercury show a peculiar yearly variability, with two intensity maxima at aphelion and perihelion. Here we present an analytical model for the total Na exosphere content, and we compare our results with ground-based observations. The model is able to reproduce the observed data, both in magnitude and in the seasonal variability. The combined effect of the planetary rotation with the modulation of sources and losses magnitude along the orbit, is able to produce a source of Na at dawn, which is needed to explain the observed maximum at aphelion. Also, we demonstrate that a process producing a consistent Na supply rate at the nightside, which can either be plasma or micrometeoroid precipitation, is needed as well. With the help of the model, we also propose a possible explanation for the dusk enhancement of Na that was seen in the MESSENGER data during the inbound leg of Mercury's orbit.

How to cite: Mura, A., Plainaki, C., Milillo, A., Mangano, V., Alberti, T., Massetti, S., Orsini, S., Moroni, M., De Angelis, E., Rispoli, R., and Sordini, R.: The Yearly Variability of the Sodium Exosphere of Mercury: a Toy Model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6215, https://doi.org/10.5194/egusphere-egu23-6215, 2023.

Europa is the innermost of Jupiter's three large icy moons. The existence of a torus of neutral gas in Europa's orbit has been inferred from in-situ plasma measurements as well as remote mapping of energetic neutral atoms around Jupiter. Simulations suggest that such a neutral gas torus can be sustained by escape from Europa’s global atmosphere and consists primarily of molecular hydrogen. Recently, the Juno spacecraft confirmed the torus through measurements of H₂⁺ ions.  However, the neutrals in this torus have never been observed more directly. Here we present observations by the highly sensitive Cosmic Origins Spectrograph of the Hubble Space Telescope (HST/COS) from 2020 and 2021. COS scanned the equatorial plane of the Jupiter system across the orbital distance of Europa between 8 and 10 planetary radii west of the planet . We report constraints from the COS high-resolution spectra on the primary neutral gasses (H₂, H, O, and O₂) near Europa's orbit and compare them to simulation results from the neutral torus model developed by Smith et al. (2019).

How to cite: Roth, L., Smith, H. T., Yoshioka, K., Becker, T., Blöcker, A., Cunningham, N., Ivchenko, N., Retherford, K., Velez, M., Saur, J., and Tsuchiya, F.: Observational constraints on the water group torus in the orbit of Jupiter moon Europa, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11814, https://doi.org/10.5194/egusphere-egu23-11814, 2023.

How much Io's SO₂ atmosphere is driven by direct volcanic outgasing or the sublimation of SO₂ surface frost is still debated. Since the sublimation supported part of the atmosphere is highly surface temperature dependent, the atmosphere is expected to have a lower SO₂ column density on the nightside consistent with observations of a decreased column density in eclipse. Furthermore, the atmosphere is observed to be thicker in equatorial regions compared to the poles and when Jupiter is in Perihelion.
To investigate how well observed structures of Io's SO₂ distribution can be explained with a purely sublimation driven atmosphere, we developed a time dependent surface temperature model including the effect of thermal inertia. Analyzing the conductive heat transfer from Io's surface towards its interior and vice versa, which is mainly determined by the thermal diffusivity α, allows us to show that many observations can be well explained by assuming a sublimation dominated atmosphere. Simulations show that α=3.1x10^-6 m² / s yields an averaged atmospheric SO₂ column density decreasing from 10¹⁶ to 2.5x10¹⁴ cm^-2 from the equator to the poles. In a parameter study regarding the thermal inertia we discuss the influence of different values of the thermal inertia on the diurnal surface temperature and column density variation and find that a thermal diffusivity lower by a factor of 10 results in an atmosphere having both features, a less pronounced latitudinal dependence but a strong day-night asymmetry. Due to Io's inclination, we also find features of the surface temperature and column density that vary seasonally. 

How to cite: Dott, A.-C., Saur, J., Schlegel, S., and Strobel, D.: Latitudinal and Longitudinal Structure of Io's Atmosphere explained by an Atmosphere that is purely Sublimation Driven, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16013, https://doi.org/10.5194/egusphere-egu23-16013, 2023.

We explore the parameter space for the contribution to Callisto's H corona observed by the Hubble Space Telescope from sublimated H₂O and radiolytically produced H₂ using the Direct Simulation Monte Carlo (DSMC) method. The spatial morphology of this corona produced via photo- and magnetospheric electron impact-induced dissociation is described by tracking the motion of and simulating collisions between the hot H atoms and thermal molecules including a near-surface O₂ component. Our results presented indicate that sublimated H₂O produced from the surface ice, whether assumed to be intimately mixed with or distinctly segregated from the dark non-ice or ice-poor regolith, cannot explain the observed structure of the H corona. On the other hand, a global H₂ component can reproduce the observation, and is also capable of producing the enhanced electron densities observed at high altitudes by Galileo's plasma-wave instrument, providing the first evidence of H₂ in Callisto's atmosphere. Finally, we discuss the implications of these results, in particular how they compare to Europa and Ganymede.

How to cite: Carberry Mogan, S., Tucker, O. J., Johnson, R. E., Roth, L., Alday, J., Vorburger, A., Wurz, P., Galli, A., Smith, H. T., Oza, A. V., Liuzzo, L., and Poppe, A. R.: Callisto’s atmosphere: First evidence for H2, and the implications this has for Europa’s and Ganymede’s atmosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8541, https://doi.org/10.5194/egusphere-egu23-8541, 2023.

The samples returned from the near-Earth asteroid (162173) Ryugu by the Hayabusa2 spacecraft provide the first opportunity for laboratory study of space weathering signatures on the most abundant C-type asteroids. Many (about 60%) of them are thought to have experienced high degrees of the aqueous alteration as shown in CI and CM carbonaceous chondrites. Hayabusa2 measured in situ near-infrared reflectance spectra of Ryugu using the NIRS3 spectrometer. The shallow 2.7-µm absorption band in the spectra was interpreted as a signature of thermal metamorphism or solar radiation heating. However, all the investigations of Ryugu grains performed to date show that the Ryugu materials are genetically common to CI chondrites. The Ryugu grains are abundant in phyllosilicates (saponite and serpentine), magnetite, Fe-Ni sulfides, and carbonates. This study about the space weathering of Ryugu grains explains this discrepancy. Ryugu is exposed to the major agents of space weathering of airless bodies. However, the resultant space-weathering products are substantially different from that of the Moon and Itokawa, both of which are composed of anhydrous minerals. Weathered Ryugu grains show areas of surface amorphization and partial melting of phyllosilicates, in which reduction from Fe³⁺ to Fe²⁺ and dehydration developed. Comparison of space-weathered materials with the run products of a helium irradiation experiment on non-space-weathered grains and of laser irradiation experiments of Murchison CM chondrite shows that the amorphization of phyllosilicates may be caused by solar wind irradiation and the partial melting, by micrometeoroid impact heating. Space weathering likely contributed to dehydration by dehydroxylation of Ryugu surface phyllosilicates that had already lost interlayer water molecules and to the weakening of the 2.7-µm hydroxyl (–OH) band in reflectance spectra. For C-type asteroids in general, this indicates that a weak 2.7-µm band can signify space weathering-induced surface dehydration, rather than bulk volatile loss.

How to cite: Noguchi, T. and the the Hayabusa2 Initial Analysis “Sand” Team and the Hayabusa2 Initial Analysis Team Core: Space weathering observed on the samples returned from Ryugu, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4647, https://doi.org/10.5194/egusphere-egu23-4647, 2023.

Irradiation by energetic ions, electrons, and UV photons induces sputtering and chemical processes (radiolysis) on the surfaces of icy moons and comets. Radiolysis of water ice has important implications for the chemistry and evolution of these celestial bodies. In this work, we carried out a series of laboratory experiments to investigate the products of radiolysis and the retention of O₂ in porous water ice samples when irradiated with high-energy electrons.

To conduct our experiments, we irradiated two types of water ice samples with high energy electrons (0.5 keV to 5 keV ) and measured the resulting chemical species using time of flight mass spectrometry. The experiments were performed under conditions replicating the icy moons’ surface conditions ( K and ^-7 mbar). Our results showed production of H₂ and O₂ radicals, but other predicted radiolysis species, such as H₂O₂ and O₃, were not detected so far; their abundances remain below 0.005 by number compared to the release of O₂. This is in contrast to previous studies, which have reported the production of OH and H₂O₂ through the radiolysis of water ice.

We also studied the retention of oxygen in the ice. By computing the timescales of rise for the O₂ signal upon irradiation, we observed that it rises faster for non-pristine (follow-up) ice irradiations. This suggests that O₂ (or an O₂ precursor) produced during the first irradiation can be retained in the ice.

For some irradiations, the electron energy and current were chosen higher to provoke the water ice's sublimation. The water release showed different properties depending on the porosity and grain size of the irradiated ice.

Overall, our results contribute to our understanding of the radiolysis of water ice and its role in the chemistry and evolution of ice-covered bodies in the solar system. Further studies will be needed to fully understand the factors that influence the production and retention of different chemical species during the radiolysis of water ice.

How to cite: Tinner, C., Galli, A., Bär, F., Pommerol, A., Rubin, M., Vorburger, A., and Wurz, P.: Electron-induced radiolysis of water ice and the buildup of O2, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7540, https://doi.org/10.5194/egusphere-egu23-7540, 2023.

The study of small bodies in our solar system is fundamental for understanding its youth and evolution. These "primitive" bodies are "undifferentiated" (their components did not separate according to their density, irreversibly altering their mineralogy). They have evolved very little since their birth, spurring a composition relatively close to that of the primordial proto-planetary disk (Scott et al. 2018). However, other processes such as thermal alteration, aqueous alteration, shocks, or space weathering can affect these bodies’ surfaces. This may introduce certain compositional biases in remote-sensed data focusing on the surface of these bodies. Therefore, it is paramount to understand the processes affecting the surface of primitive asteroids to correctly assess their composition.

There are several ways to study the surface of primitive asteroids, such as remotely, by acquiring spectroscopic data (gaining access to surface chemical and mineralogical composition). It is also possible to study these bodies in a laboratory environment, by working on analogous materials such as certain classes of "primitive" meteorites (Greenwood et al. 2020) (carbonaceous chondrites), on terrestrial analogues such as hydrated silicates - which dominates the mineral composition of “primitive” bodies (Usui et al. 2018), or directly on extra-terrestrial materials brought back by sample return missions (Yokoyama et al. 2022, Nakalura et al. 2022, Noguchi et al. 2022).

In this work, we replicate in a laboratory environment the effects of space weathering (SpWe) on the surface of primitive asteroids. We focus on the effects of solar wind, the dominant SpWe process on "young" surfaces (Brunetto et al. 2015, Clark et al. 2002). We have chosen three terrestrial minerals analogous to a "primitive" surface - three hydrated minerals (two serpentines and one saponite) - of which we have produced several pellets which have been bombarded using He and Ar ions. In doing so, we made analogous materials of weathered primitive surface matter. These analogues were then characterized by infrared spectroscopy, from the visible to the far-infrared range, to study chemical changes prompted by ion bombardment. This was done by investigating how certain spectroscopic features – characteristic of hydrated silicates – changed upon ion-bombardment. We detected several effects, such as darkening in the visible range, visible slope reddening and bluing as well as a systematic shift towards longer wavelength affecting the position of several spectroscopic features.

This was followed by a study at a smaller scale, using electron microscopy. We first characterized the surface of our weathered analogues using scanning electron microscopy, and then investigated the morphological and physicochemical changes taking place in the bombarded layer, at a nanometre scale, using transmission electron microscopy. Strong vesiculation effects of various kinds were identified in the ion bombarded amorphized layers, as well as textural changes and some elemental concentration evolution (such as the loss of oxygen in the utmost top surfaces, preferential amorphization of magnesium, etc.).

The coupling between these two techniques, Vis/IR spectroscopy and electron microscopy, has allowed us to start probing the relations between SpWe induced effects seen at different scales.

How to cite: Rubino, S., Lantz, C., Aléon-Toppani, A., Baklouti, D., Djouadi, Z., Troadec, D., Palomba, E., Borondics, F., Leroux, H., and Brunetto, R.: Combining Visible/Infrared Spectroscopy and Transmission-Electron-Microscopy To Investigate Space-Weathering Induced Changes In Hydrated Silicates, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5262, https://doi.org/10.5194/egusphere-egu23-5262, 2023.

Introduction: Space weathering by ion irradiation is ubiquitous on the surfaces of airless bodies in the Solar System. Sputtering occurs when solar wind (SW) or magnetosphere ions (MI) impact the suraces of bodies in space. Asteroids and moons are too small to maintain a significant atmosphere, and therefore they are directly exposed to ionizing radiation from the solar wind and magnetospheric plasmas. Incident ions can transfer sufficient energy to surface species to cause them to desorb and potentially escape to space. A small fraction of the sputtered species can escape as ions, called sputtered secondary ions (SSI). Mass, charge, and energy analysis of the sputtered ions using secondary ion mass spectrometry is highly diagnostic of the irradiated surface composition. The upcoming JAXA MMX mission will carry a Mass Spectral Analyzer (MSA) instrument will be capable of making measurements of SSI around its target bodies Phobos and Deimos (P&D). However, there is currently limited estimates of SSI yields from relevant surface compositions under relevant irradiation conditions, and the expected SSI fluxes around P&D are not well constrained.

Background: Although P&D are exposed to both the SW and MI and SSI are expected to be present throughout their orbits. However, several challenges arise when attempting to derive a precise surface composition from a measured SIMS spectra, or when estimating the expected count rates and elemental ratios that will be observed by MSA for a given composition: (i) the relative abundances measured by SIMS are not directly correlated with the actual surface composition, and (ii) the relative and absolute SSI yields (# of SSI ejected per incident ion) likely depend on the surface chemistry and exposure history, and on the incident ion type and energy.

Results: A combined computational and experimental approach has been used in order to better constrain the solar wind sputtering rates of small, rocky bodies. First, a series of SIMS measurements in the laboratory were carried out to determine the relative ion sputtering ratios from several lunar samples of known composition. Then, using Monte Carlo simulations of sputtering due to both solar wind and magnetosphere ions and the measured SSI energy distributions to determine the total sputtering yields, the total abundance and relative composition of sputtered ions can be determined for an arbitrary small body. This work will (1) estimate the the SSI yields from analog Mars and Carbonaceous Chondrite analog materials and correlate the expected yields with the surface composition, and (2) provide estimates the SSI fluxes and densities during their orbits around Mars. Further, this work will demonstrate how measurement of the elemental ratios of SSI can be used to estimate the potential origins scenarios for small bodies.

How to cite: Schaible, M., Morrissey, L., Sarantos, M., and Johnson, R.: Determining the Sputtered Secondary Ion Densities at Phobos and Deimos: A combined computational and experimental study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16977, https://doi.org/10.5194/egusphere-egu23-16977, 2023.

One of the influences that the Moon experiences in the space environment is the bombardment of the surface by solar wind ions, mostly protons and alpha particles. A consequence of this irradiation is the liberation of material through the process of sputtering. The ejected particles subsequently take part in the formation of the lunar exosphere [1]. Understanding the sputtering of the Moon’s surface and experimentally constraining the process quantities like sputter yield and angular distribution of ejecta is thus necessary to properly model the exosphere creation [2].

For this purpose, previous studies used analogue materials to investigate their erosion. We now present studies of two types of samples prepared from actual lunar soil obtained during the Apollo 16 mission: First, regolith material was pressed into stainless steel holders to form pellets, analogue to the sample preparation described in [3]. Apart from the application of pressure necessary for the pellet formation, the specimens were not further altered. Moreover, pulsed laser deposition was carried out to grow thin films onto quartz resonators using one such pellet as donor. While these films were checked to have the same chemical composition as the source material, they are however flat and vitreous.

Using such a resonator with the deposited lunar material as a Quartz Crystal Microbalance (QCM), we studied the mass depletion of the sample layer due to He⁺ and H⁺ ion bombardment in situ and in real time. Because this direct means of measuring the sputter yield cannot be applied to the rough and more pristine regolith pellets, another QCM was used. This second microbalance maintains a fixed distance d to the centre of the irradiated target and allows for variation of the polar angle β with respect to the target surface normal. The setup enables us to probe the angular distribution of particle flux by collecting a fraction of the liberated material. It is sketched in figure 1. With the thin film irradiations used as calibration, these differential sputter yields give indirect insight into the total mass sputtered away as a function of ion incidence angle. This approach has already proven to work well with analogue materials for the surfaces of celestial bodies [4]. We will present our experimental findings for both thin film and pellet irradiations along with simulation approaches to model these results. This study represents an important extension of previous experiments to actual lunar surface samples and will thus provide essential insights into constraining sputtering of the surface of the Moon and other planetary bodies.

Figure 1: Illustration of the experimental setup. Using the catcher QCM, the sputtered ejecta flux can be probed along the emission angle β under various incidence angles α.

[1] Hapke, B. et al; J. Geophys. Res. 106 (2001): 10039
[2] Wurz, P. et al; Icarus 192 (2007): 486
[3] Jäggi, N. et al; Icarus 365 (2021): 114492
[4] Biber, H. et al; Planet. Sci. J. 12 (2022)

How to cite: Brötzner, J., Biber, H., Jäggi, N., Nenning, A., Szabo, P. S., Odin, K., Rizek, B., Galli, A., Wurz, P., and Aumayr, F.: Quantifying sputter yields of lunar soils, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16456, https://doi.org/10.5194/egusphere-egu23-16456, 2023.

Titan's palaeoclimate after the onset of the putative last major methane outgassing event 700 Myr ago is simulated by a global climate model. If the atmosphere was methane-depleted prior to outgassing, outgassed methane initially causes warming due to increased greenhouse effect. Further outgassing leads to methane snowfall, which in turn cools the troposphere and surface by an ice-albedo feedback and thereby initiates a lengthy ice age. Formation of ice sheets begins in the polar region, but with increasing methane inventory the entire globe is eventually covered by surface methane frost as thick as 100 m, with local accumulation on elevated terrains. Among various time-dependent input parameters the methane inventory by far exerts the greatest control over the climate evolution. As Titan's climate transitions from a dry state via a partially ice-covered state to a globally ice-covered state, the circulation and precipitation pattern change profoundly and the tropospheric temperature further decreases. Globally ice-covered snowball Titan is characterized by weak meridional circulation, weak seasonality and widespread snowfall. Frost ablation begins after the end of outgassing due to photochemical destruction of atmospheric methane. It is conceivable that Titan's polar seas resulted from melting of the polar caps within the past 10 Myr and subsequent drainage to the polar basins. Surface methane frost could only melt when the frost retreated to the polar region, which led to global warming by lowering of the surface albedo at low latitudes and increased greenhouse effect.

How to cite: Tokano, T. and Lorenz, R. D.: Palaeoclimate evolution on Titan after episodic massive methane outgassing simulated by a global climate model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2061, https://doi.org/10.5194/egusphere-egu23-2061, 2023.

Introduction:  Solar wind, which comprises high energy hydrogen ions, continuously strikes the lunar surface, which is rich in oxygen. This presents an opportunity for hydroxylation - the creation of OH on lunar soil. Both OH and H2O have been detected on the lunar surface, with some variability in abundance throughout the lunar day. It is important to understand how space weathering contributes to the production and proliferation of hydrogen-bearing resources such as water within the lunar environment.

OH shows a distinct absorption feature in the infrared (IR) at ~3 µm^-1 that can be readily studied. Fourier Transform Infrared (FTIR) Spectroscopy is a fast and accurate way to detect changes in the infrared spectra of lunar soil. Previous studies have examined the changes in IR spectra of amorphous silica and olivine, as well as lunar soil before and after hydrogen irradiation. However, the evolution of the OH band and other IR features has not been studied during hydrogen radiation itself. It is especially important to not expose the samples to terrestrial air, which will contaminate the samples with water.

Method and Results: We present FTIR spectra on Apollo-era soil samples obtained simultaneously with high energy hydrogen plasma irradiation, similar to the solar wind. Samples are first prepared by baking under vacuum to drive off any surface water. Samples are also brought through thermal cycling and heated to 400K (lunar dayside maximum temperature) in-situ, and changes in their IR spectra are reported. Comparisons between Apollo samples with different minerology and with a control of crushed SiO₂ are also provided. Results show broad but distinct growths in the 3 µm^-1 absorption band for lunar samples compared to a sharper peak for SiO₂. Since the samples are not exposed to terrestrial water during measurements, the evidence of hydroxylation presented is likely due to hydrogen irradiation.

How to cite: Yeo, L. H., McLain, J., and Killen, R.: Hydroxylation of Lunar Soil with Solar Wind, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9917, https://doi.org/10.5194/egusphere-egu23-9917, 2023.