PS4.1 | Atmospheres, exospheres, and surfaces of terrestrial planets, satellites, small bodies, and exoplanets
EDI
Atmospheres, exospheres, and surfaces of terrestrial planets, satellites, small bodies, and exoplanets
Convener: Arnaud Beth | Co-conveners: Arianna Piccialli, Audrey Vorburger, Quentin NenonECSECS, Rosario Brunetto, André Galli, Francois Leblanc
Orals
| Thu, 27 Apr, 14:00–17:55 (CEST)
 
Room 1.61/62
Posters on site
| Attendance Thu, 27 Apr, 16:15–18:00 (CEST)
 
Hall X4
Posters virtual
| Attendance Thu, 27 Apr, 16:15–18:00 (CEST)
 
vHall ST/PS
Orals |
Thu, 14:00
Thu, 16:15
Thu, 16:15
This session primarily focuses on neutral atmospheres, surfaces, and exospheres of terrestrial bodies other than the Earth. This includes not only Venus and Mars, but also exoplanets with comparable envelopes, small bodies and satellites carrying dense atmospheres such as Titan, exospheres such as Ganymede, or with a surface directly exposed to space like asteroids. We welcome contributions dealing with processes affecting the atmospheres of these bodies, from the surface to the exosphere. We invite abstracts concerning observations, both from Earth or from space, modeling and theoretical studies, or laboratory work. Comparative planetology abstracts will be particularly appreciated.

Orals: Thu, 27 Apr | Room 1.61/62

Chairpersons: Quentin Nenon, André Galli
Atmospheres and exospheres
14:00–14:20
|
EGU23-7647
|
PS4.1
|
solicited
|
On-site presentation
David Ehrenreich

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.

14:20–14:30
|
EGU23-2829
|
PS4.1
|
On-site presentation
Cédric Gillmann, Johnny Seales, Pedram Hassanzadeh, and Adrian Lenardic

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.

14:30–14:40
|
EGU23-14084
|
PS4.1
|
ECS
|
On-site presentation
Nanna Bach-Møller, Christiane Helling, Uffe Gråe Jørgensen, and Martin Bødker Enghoff

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.

14:40–14:50
|
EGU23-2306
|
PS4.1
|
ECS
|
On-site presentation
Jiachen Liu, Jun Yang, Yixiao Zhang, and Zhihong Tan

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.

14:50–15:00
|
EGU23-9581
|
PS4.1
|
On-site presentation
John Clarke, Dolon Bhattacharyya, Majd Mayyasi, Valery Shematovich, Dimitri Bisikalo, Jean-Yves Chaufray, Ed Thiemann, Jasper Halekas, Carl Schmidt, Jean-Loup Bertaux, Michael Chaffin, and Nick Schneider

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.

15:00–15:10
|
EGU23-1968
|
PS4.1
|
On-site presentation
Kei Masunaga, Naoki Terada, Nao Yoshida, Yuki Nakamura, Takeshi Kuroda, Kazuo Yoshioka, Yudai Suzuki, Hiromu Nakagawa, Tomoki Kimura, Fuminori Tsuchiya, Go Murakami, Atsushi Yamazaki, Tomohiro Usui, and Ichiro Yoshikawa

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 (LS=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.

15:10–15:20
|
EGU23-6215
|
PS4.1
|
solicited
|
On-site presentation
Alessandro Mura, Christina Plainaki, Anna Milillo, Valeria Mangano, Tommaso Alberti, Stefano Massetti, Stefano Orsini, Martina Moroni, Elisabetta De Angelis, Rosanna Rispoli, and Roberto Sordini

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.

15:20–15:30
|
EGU23-11814
|
PS4.1
|
On-site presentation
Lorenz Roth, H. Todd Smith, Kazuo Yoshioka, Tracy Becker, Aljona Blöcker, Nathaniel Cunningham, Nickolay Ivchenko, Kurt Retherford, Michael Velez, Joachim Saur, and Fuminori Tsuchiya

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.

15:30–15:40
|
EGU23-16013
|
PS4.1
|
ECS
|
On-site presentation
Anne-Cathrine Dott, Joachim Saur, Stephan Schlegel, and Darrell Strobel

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.

Coffee break
Chairperson: Quentin Nenon
16:15–16:25
|
EGU23-8541
|
PS4.1
|
ECS
|
On-site presentation
Shane Carberry Mogan, Orenthal J. Tucker, Robert E. Johnson, Lorenz Roth, Juan Alday, Audrey Vorburger, Peter Wurz, Andre Galli, H. Todd Smith, Apurva V. Oza, Lucas Liuzzo, and Andrew R. Poppe

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.

Surface and space weathering
16:25–16:45
|
EGU23-4647
|
PS4.1
|
solicited
|
Virtual presentation
Takaaki Noguchi and the the Hayabusa2 Initial Analysis “Sand” Team and the Hayabusa2 Initial Analysis Team Core

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.

16:45–16:55
|
EGU23-1299
|
PS4.1
|
ECS
|
On-site presentation
|
Noah Jäggi, Andreas Mutzke, Herbert Biber, Paul S. Szabo, Johannes Brötzner, Friedrich Aumayr, Peter Wurz, and André Galli

The sputtering of material is mostly modeled using Binary Collision Approximation programs. Several advances were made in the last few years focusing on modeling mineral sputtering by ion impacts relevant for rocky planets exposed to solar wind. The most recent contribution, from Biber et al. [1], includes not only sputter yields, but also angular distribution data for the mineral enstatite. The existing data, although scarce, are important to validate mineral sputter simulations. A widely applicable model is integral for obtaining and interpreting information of particles ejected from exposed rocky bodies such as Mercury and the Moon. Moreover, ease of use is crucial whenever a new approach is proposed, which is to compete with the default model found in the user-friendly, but inaccurate TRIM code [2]. 

To best recreate experimental data from mineral sputtering, previously suggested approaches rely on increased surface binding energies as well as increased sample densities [3,4]. We review the capabilities and limitations of these and propose a new model to best approximate experimental results. In contrast to the earlier models, our approach achieves unprecedented agreement with available experimental data under normal incidence (Fig. 1). It thereby does not require any manual adjustments of simulation parameters to achieve realistic mineral densities and does not depend on computationally intensive determination of species-specific surface binding energies [4].

The new model considers a surface binding energy for species leaving the sample as well as a bulk binding energy within the sample based on the enthalpy of formation. The latter prevents long collision cascades due to energy loss in the sample whenever a bond of a mineral-forming compound (i.e., an oxide or sulfide) is broken. Favoring short collision cascades leads to a more prominent forward-tilt of the ejecta distribution as it is seen in experiments. The increased energy loss within the sample also causes a peak broadening in the energy distribution of ejected particles whilst shifting the peak positions slightly towards larger energies. We expect to see this behavior on oxygen-bearing minerals as the same tendencies were observed in energy distributions of irradiated oxidized metals [5,6,7]. While we wait for further experimental data our improved quantitative formulation of the mineral sputter process is a valuable contribution for achieving state of the art exosphere models for the Moon and Mercury.

Fig. 1: Sputter yield of various models in SDTrimSP compared to TRIM and experimental data [1]. Short forms: SB — surface binding energies (default); BB — bulk binding energies; SBB-C — combined SB and BB model, differentiating bound and free atoms within predefined compounds. 

 

[1] Biber, H., et al. (2022). Planet. Sci. J., 3, 271.

[2] Hobler, G. (2013). Nucl. Instrum. Methods Phys. Res. B, 303, 165–169.

[3] Szabo, P.S., et al. (2020). Astrophys. J., 891(1), 100.

[4] Morrissey, L. S., et al. (2022). Astrophys J. Lett., 925(1), L6.

[5] Dullni, E. (1984). Nucl. Instrum. Methods Phys. Res. B, 2(1–3), 610–613.

[6] Wucher, A., & Oechsner, H. (1986). Nucl. Instrum. Methods Phys. Res. B, 18(1–6), 458–463.

[7] Wucher, A., & Oechsner, H. (1988). Surf. Sci., 199(3), 567–578. 

How to cite: Jäggi, N., Mutzke, A., Biber, H., Szabo, P. S., Brötzner, J., Aumayr, F., Wurz, P., and Galli, A.: A mineral sputter model in agreement with solar wind ion irradiation experiments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1299, https://doi.org/10.5194/egusphere-egu23-1299, 2023.

16:55–17:05
|
EGU23-7540
|
PS4.1
|
ECS
|
On-site presentation
Chantal Tinner, André Galli, Fiona Bär, Antoine Pommerol, Martin Rubin, Audrey Vorburger, and Peter Wurz

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.

17:05–17:15
|
EGU23-5262
|
PS4.1
|
ECS
|
Virtual presentation
Stefano Rubino, Cateline Lantz, Alice Aléon-Toppani, Donia Baklouti, Zahia Djouadi, David Troadec, Ernesto Palomba, Ferenc Borondics, Hugues Leroux, and Rosario Brunetto

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.

17:15–17:25
|
EGU23-16977
|
PS4.1
|
ECS
|
On-site presentation
Micah Schaible, Liam Morrissey, Menelaos Sarantos, and Robert Johnson

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.

17:25–17:35
|
EGU23-16456
|
PS4.1
|
ECS
|
On-site presentation
Johannes Brötzner, Herbert Biber, Noah Jäggi, Andreas Nenning, Paul Stefan Szabo, Killian Odin, Bernhard Rizek, André Galli, Peter Wurz, and Friedrich Aumayr

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.

17:35–17:45
|
EGU23-2061
|
PS4.1
|
On-site presentation
Tetsuya Tokano and Ralph D. Lorenz

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.

17:45–17:55
|
EGU23-9917
|
PS4.1
|
On-site presentation
Li Hsia Yeo, Jason McLain, and Rosemary Killen

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.

Posters on site: Thu, 27 Apr, 16:15–18:00 | Hall X4

Chairperson: André Galli
X4.293
|
EGU23-16730
|
PS4.1
Ottaviano Rüsch and Markus Patzek

Thermal fatigue driven by diurnal temperature variations can lead to the physical modifications of rocks and boulders that populate airless surfaces [1-2]. These modifications affect regolith evolution, e.g., particle size, porosity and roughness, and thus influence reflected and emitted radiation observed by spacecraft, Earth- and space-based telescopes. In order to study in detail how this process affects rocks of different mineralogy and under different environments (temperature, vacuum) we use a custom-made thermal cycling chamber operating in high vacuum and at cryogenic temperatures. The investigation on achondrite meteorite samples demonstrated moderate cracking after thermal cycling relative to chondritic samples and revealed a new phenomenon, i.e., formation and detachment of micro-flakes for lunar anorthositic samples [3]. The investigation of chondritic samples subjected to thermal cycling revealed i) formation and extension of cracking due to thermal fatigue for Jbilet Winselwan (CM2), Murchison (CM2) and Tagish Lake (C2ung); ii) absence of newly formed cracks for El Hammami (H5) and Allende (CV3), iii) absence of micro-flaking for all the above-mentioned samples. In addition, we find that in CM chondrites, cracking is often associated with hydrous fine-grained rims that surround chondrules and, in some cases, cracks diverging radially from the chondrules through the rim into the clastic matrix. These results illustrate how the mineralogy and texture, in particular the spatial context with minerals of different coefficient of thermal expansion (hydrous phyllosilicates and olivine/pyroxene), play an important role in crack formation and/or extension.

References : [1] Delbo M. et al. (2014) Nature, 508(7495), 233-236, doi:10.1038/nature13153. [2] Molaro J. L. et al. (2015) JGR: Planets, 120(2), 255-277, doi:10.1002/2014JE004729. [3] Patzek M. and Rüsch O. (2022) JGR: Planets 127.10. doi:10.1029/2022JE007306

How to cite: Rüsch, O. and Patzek, M.: Mineralogical control of fracturing and micro-flaking due to thermal fatigue, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16730, https://doi.org/10.5194/egusphere-egu23-16730, 2023.

X4.294
|
EGU23-4363
|
PS4.1
|
ECS
Malathe Khalil, Sanchit Chhabra, Marko Gacesa, Amal Al Ghaferi, and Nayla El-Kork

The Martian atmospheric gas loss may have played a role in transforming Mars from a warmer, water-containing planet into a cold and dry one. This loss is attributed to different phenomena, including photodissociation of H2O followed by Jeans escape and photochemical escape of hot O atoms.  It was proposed that collisions with hot (super-thermal) neutral atoms can eject light species from the atmosphere such as He [1], D[2], H2 [3], and OH[4]. Here, collisions with super-thermal oxygen atoms are the most important because of its kinetic energy and abundance. Carbon monoxide (CO) has been used as a probe for studying the planet’s atmospheric composition and the dynamics involved [5]. In this study, we computed the elastic and inelastic integral and differential cross-sections for CO collisions with energetic O(3P) and its isotopes using a full coupled-channel quantum mechanical formalism at collision energies from 0.4 to 5 eV. The O+CO interactions were described using recently constructed potential energy surfaces of 3A′, 3A″, and 23A″ symmetry [6], dissociating to the atomic ground state. The state-to-state, elastic, and inelastic cross-sections were calculated for individual surfaces as well as their statistical average [7]. We applied the new cross sections in a simple 1D column transport model to provide revised escape and energy transfer rates of O(3P) and its isotopes in thermal CO gas, at the conditions corresponding to the upper atmosphere of Mars, where CO is abundant.

References:

[1]       S. Bovino, P. Zhang, F. A. Gianturco, A. Dalgarno, and V. Kharchenko, “Energy transfer in O collisions with He isotopes and Helium escape from Mars,” Geophys. Res. Lett., vol. 38, no. 2, pp. 2–6, 2011, doi: 10.1029/2010GL045763.

[2]       P. Zhang, V. Kharchenko, M. J. Jamieson, and A. Dalgarno, “Energy relaxation in collisions of hydrogen and deuterium with oxygen atoms,” J. Geophys. Res. Sp. Phys., vol. 114, no. 7, pp. 1–14, 2009, doi: 10.1029/2009JA014055.

[3]       M. Gacesa, P. Zhang, and V. Kharchenko, “Non-thermal escape of molecular hydrogen from Mars,” Geophys. Res. Lett., vol. 39, no. 10, pp. 1–6, 2012, doi: 10.1029/2012GL050904.

[4]       M. Gacesa, N. Lewkow, and V. Kharchenko, “Non-thermal production and escape of OH from the upper atmosphere of Mars,” Icarus, vol. 284, pp. 90–96, 2017, doi: 10.1016/j.icarus.2016.10.030.

[5]       M. Zhang and D. Shi, “Transition properties of the X 1 Σ + , I 1 Σ − , A 1 Π , D 1 Δ , B 1 Σ + , and a 3 Π states of carbon monoxide,” Comput. Theor. Chem., vol. 1202, no. May, p. 113302, 2021, doi: 10.1016/j.comptc.2021.113302.

[6]       R. L. Ja, G. M. Chaban, and M. Field, “Collisional Dissociation of CO : ab initio Potential Energy Surfaces and Quasiclassical Trajectory Rate Coe cients,” pp. 1–54, 2019.

[7]       S. Chhabra, M. Gacesa, M. S. Khalil, A. Al Ghaferi, and N. El-kork, “A quantum-mechanical investigation of O(3P) + CO scattering cross sections at superthermal collision energies,” Mon. Not. R. Astron. Soc., no. October, 2022, doi: https://doi.org/10.1093/mnras/stac3057.

 

How to cite: Khalil, M., Chhabra, S., Gacesa, M., Al Ghaferi, A., and El-Kork, N.: A quantum-mechanical investigation of O(3P) + CO scattering cross sections at superthermal collision energies, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4363, https://doi.org/10.5194/egusphere-egu23-4363, 2023.

X4.295
|
EGU23-8602
|
PS4.1
|
ECS
Shane R. Carberry Mogan, Lucas Liuzzo, Andrew R. Poppe, and Sven Simon

Herein we constrain the radiolytic production rate of O2 from Callisto's exposed ice patches as well as the corresponding steady-state abundance of O2 in Callisto's atmosphere. That is, by simulating the fluxes of thermal plasma and energetic particles irradiating Callisto's surface, taking into account energy deposition within the atmosphere, we determine the initial source flux of O2 to estimate the corresponding column density for Callisto's O2 component, which we compare to those suggested in the literature. This study provides constraints for Callisto's O2 atmosphere in preparation for future observations, particularly those that will be made by the JUpiter ICy moons Explorer (JUICE) and Europa Clipper spacecraft, as well as the Hubble Space Telescope (HST). Further, based on this analysis at Callisto, we can better our understanding on how the atmospheres of other icy satellites in the Solar System can evolve to their observed state.

How to cite: Carberry Mogan, S. R., Liuzzo, L., Poppe, A. R., and Simon, S.: Constraining the radiolytic production of Callisto’s O2 atmosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8602, https://doi.org/10.5194/egusphere-egu23-8602, 2023.

X4.296
|
EGU23-1163
|
PS4.1
|
ECS
|
Sébastien Verkercke, Jean-Yves Chaufray, François Leblanc, Eduardo Bringa, Diego Tramontina, Liam Morrissey, and Adam Woodson

Airless planetary bodies’ surfaces, such as the Moon’s or Mercury’s, are composed of porous regoliths which interact directly with the impinging solar wind. In the case of the Moon, this incoming flux of solar protons has been observed to be partially neutralized and backscattered as Energetic Neutral Atoms (ENA) with reflection coefficients believed to be ranging between 0.1 and 0.2 depending on the study and/or the measurement. Such a large range of reflection coefficients reflects the diversity in the regolith’s interactions with the solar wind and underlines the lack of understanding of the lunar regolith and its influence on the particles impacting it.

The ENA flux is thought to depend on the structure of the upper regolith layer and the solar wind characteristics. By using a model combining a Monte Carlo approach to describe a solar proton’s journey through the lunar surface, with molecular dynamics to characterize its interactions with the regolith’s grains, we highlighted key parameters which influence the backscattered ENA flux and analyzed their roles in these interactions. To describe the structure of the lunar regolith we used the open-source code LAMMPS Molecular Dynamics Simulator, which allows a realistic description of grain-on-grain contacts using a Johnson-Kendall-Roberts (JKR) contact model. The porosity of the modeled regolith is shown to be dictated by the surface energy of the grains. By considering silicate grains and a realistic range of surface energy for this material, we studied regoliths’ porosities ranging from ~0.5 to 0.85. This work showed that a large porosity favors deeper penetration of the protons inside the regolith, which increases the number of collisions, and thus the energy lost by the impinging protons and their absorption. By accounting for particular directions of observation with respect to the solar wind direction, we showed that the angular distribution of the backscattered ENA is anisotropic. We here used IBEX observations and its characteristic 90° observation angle as a demonstration of the influence of this anisotropy. We finally analyzed the effects of both the energy distribution of the hydrogen atoms after a collision with a grain and the solar wind properties on the ENA energy flux spectrum shape. The modelled spectrum was also compared to the observations of Chandrayaan-1. This work aims for a better understanding of the interactions ongoing at this interface and intents to look into the possibility to deduce information on the surface structure solely from ENA flux measurements.

How to cite: Verkercke, S., Chaufray, J.-Y., Leblanc, F., Bringa, E., Tramontina, D., Morrissey, L., and Woodson, A.: Effects of the Lunar Regolith Structure and of the Solar Wind Properties on the Backscattered Energetic Neutral Atoms Flux, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1163, https://doi.org/10.5194/egusphere-egu23-1163, 2023.

X4.297
|
EGU23-17142
|
PS4.1
Prabhakar Misra, Kennedi White, William M. Farrell, and Orenthal J. Tucker

Observations of surficial OH/H2O in regolith grains on the Moon’s surface indicate variability on diurnal timescales 1–3 consistent with the variability of the solar wind proton flux and local surface temperature. Recent Monte Carlo models accounting for hydrogen diffusion and the degassed H2 exosphere support the theory of solar wind implantation being the primary driver of the lunar hydrogen cycle 4. In this presentation, we will report modeling results of the dynamical response of surficial OH content and the H2 exosphere during a Coronal Mass Ejection event, for which the proton flux can be a factor of 20 larger than nominal solar wind conditions 5,6. Observations of the response of hydrogen in the lunar environment during a solar storm event would provide strong support for solar wind implantation being the principal mechanism producing surface OH content and H2 exosphere.

Acknowledgment: Financial support from LEADER (NASA Award# 80NSSC20M0019) is gratefully acknowledged.

1. Li, S. et al. New formation processes of lunar surface water in Earth’s magnetotail. Nat Astron Accepted, (2023).

2. Li, S. & Milliken, R. E. Water on the surface of the Moon as seen by the Moon Mineralogy Mapper: Distribution, abundance, and origins. Sci Adv 3, 1–12 (2017).

3. Grumpe, A., Wöhler, C., Berezhnoy, A. A. & Shevchenko, V. v. Time-of-day-dependent behavior of surficial lunar hydroxyl/water: Observations and modeling. Icarus 321, 486–507 (2019).

4. Tucker, O. J., Farrell, W. M. & Poppe, A. R. On the Effect of Magnetospheric Shielding on the Lunar Hydrogen Cycle. J Geophys Res Planets 126, (2021).

5. Killen, R. M., Hurley, D. M. & Farrell, W. M. The effect on the lunar exosphere of a coronal mass ejection passage. Journal of Geophysical Research E: Planets 117, 1–15 (2012).

6. Farrell, W. M. et al. Solar-Storm/Lunar Atmosphere Model (SSLAM): An overview of the effort and description of the driving storm environment. J Geophys Res Planets 117, (2012).

How to cite: Misra, P., White, K., Farrell, W. M., and Tucker, O. J.: Variation of the Moon’s Solar-Induced Hydrogen Cycle during a Solar Storm, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17142, https://doi.org/10.5194/egusphere-egu23-17142, 2023.

X4.298
|
EGU23-6979
|
PS4.1
|
ECS
Quentin Nenon, Jim Raines, and Andrew Poppe

The role and importance of solar wind ions heavier than helium for the weathering of airless body surfaces across the solar system remain debated. In addition, the contribution to surface weathering of suprathermal and energetic heavy ions, which have extremely low densities compared to thermal ions but high energy, is an open question.

In this presentation, we will take advantage of the advanced ion instrumentation and long duration of the Wind mission to finely characterize the spectrum and anisotropy of the heavy minor ions that bombard airless body surfaces. Specifically, we will combine heavy ion measurements from the Wind-SWICS (thermal ions), Wind-STICS (suprathermal), and Wind-STEP (energetic) experiments.

We will constrain the long-term averaged properties of the heavy ion populations, which are relevant for the development of long-term surface weathering effects. We will also study the heavy ion populations during solar wind events, relevant for short-term alteration effects. Finally, we will detail the impact of our ion-data-based results on the global field of space weathering.

How to cite: Nenon, Q., Raines, J., and Poppe, A.: Weathering of airless body surfaces by the heavy minor ions of the solar wind: inputs from Wind ion observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6979, https://doi.org/10.5194/egusphere-egu23-6979, 2023.

X4.299
|
EGU23-13635
|
PS4.1
|
ECS
|
Moritz Meyer zu Westram, Apurva Oza, and André Galli

Although exomoons, natural satellites beyond our solar system, are still undetectable in direct searches with state-of-the-art instruments, their existence has been hypothesized to explain various inconsistencies in exoplanetary spectra. Exogenic sources of sodium and potassium have been considered at multiple exoplanets, where abundances exceed the exoplanet’s source rates, and hydrostatic exoplanet atmospheres are limited in their ability to explain increased line broadening seen in Na & K spectra, where an orbiting body naturally provides broadening with variable ±∼10-20 km/s.
A semi-analytic atmospheric escape and evolution model dishoom approximates the minimum mass flux needed for an exomoon to provide volcanic material for the absorption of star light. We develop a 3-D test-particle Monte Carlo simulation module called SERPENS (Simulating the Evolution of Ring Particles Emergent from Natural Satellites) to be coupled to dishoom. SERPENS is designed to be highly adaptive, open-source, and easy to use. We simulate the neutral outgassing and evolution of a satellite at multiple candidate exoplanet-exomoon systems including HD189733 b II, HD209458 b I, WASP-49 A b I, HAT-P-1 b I, and WASP-96 b I, in order to provide a number density n[cm−3] and line-of-sight column density N[cm−2] map of the particle environment in a non-hydrostatic medium, characteristic of a volcanic exosphere akin to Jupiter’s Na exosphere fueled by Io. The neutral species maps are then fed into a non-hydrostatic radiative transfer model, Prometheus, which computes an exospheric spectrum that can be directly compared to ongoing ground and space-based spectra of candidate exomoon systems. We model masses ranging from Earth, Io, and Enceladus to emulate long-term effects of mass loss and present the respective particle distributions. Photoionization is set as the prime constraint for the lifetime of atoms and molecules.
In contrast to previous works, our code SERPENS focuses on exomoons and their imprint as a neutral
and plasma torus. SERPENS is designed to eject particles via sputtering and thermal evaporation at
regular time intervals allowing us to simulate an evolving cloud/torus. Multiple species including Na, K
and SO2, as well as their chemical networks, are supported.
Our results demonstrate how exomoons similar to Io, referred to as exo-Ios, can affect line-of-sight column densities depending on the phase of the exomoon at the time of observation. This means that it is possible to model time-variable spectra by taking into account the phase of the exomoon.

How to cite: Meyer zu Westram, M., Oza, A., and Galli, A.: Exo-Io Simulations of Toroidal Exospheres, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13635, https://doi.org/10.5194/egusphere-egu23-13635, 2023.

X4.300
|
EGU23-12587
|
PS4.1
|
ECS
Tanguy Bertrand, François Forget, and Emmanuel Lellouch

Triton is often seen as Pluto’s sibling, as both objects share similar sizes, densities, and atmospheric and surface ice composition. Yet Triton’s surface appearance, including its topography, surface albedo and volatile ice distribution, strongly differs from Pluto’s. For instance, Triton is relatively flat and uniformly bright, with permanent nitrogen ice deposits likely covering its entire southern hemisphere. In contrast, Pluto’s landscape includes tall mountains and deep basins, a surface with very bright and very dark features, and permanent nitrogen ice deposits located in the mid-latitudes and equatorial regions, and in particular in the topographic basin Sputnik Planitia.

These differences suggest a different geological history. In fact, Triton and Pluto are both thought to have formed beyond Neptune and then to have evolved differently. On the one side, Pluto remained in the Kuiper Belt and was hit by a twin to form the Pluto-Charon moon system. On the other side, Triton was captured by Neptune, as strongly suggested by its retrograde and highly inclined orbit around the Ice Giant planet, and its interior subsequently experienced intense tidal deformation and heating. Geological activity on Triton may still be powered today by tidal activity.  

Previous modeling studies also highlighted the importance of the Milankovitch parameters (obliquity, eccentricity, solar longitude of perihelion) on Pluto in controlling the surface temperatures and therefore the ice sublimation and condensation rates. In particular, the high obliquity of Pluto’s spin axis seems to explain the presence of massive volatile ice deposits in the equatorial regions. Could Triton’s and Pluto’s volatile ice distributions be distinct mainly because of differences in obliquity?

To answer this question, we performed new numerical simulations of Pluto’s and Triton’s volatile transport using the same climate model for both simulations, and the same initial states, but changing only the topography as well as the obliquity and orbital parameters specific to each object. The comparison of these simulations highlight the impact of obliquity in controlling the location of the permanent deposits of volatile ices on Pluto and Triton. At the conference, we will present these results and show that the impact of obliquity on Pluto and Triton, and on similar volatile-rich Transneptunian objects, goes beyond the volatile ice distribution.

How to cite: Bertrand, T., Forget, F., and Lellouch, E.: How obliquity controls the surface appearance of Triton, Pluto and other volatile-rich Transneptunian objects, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12587, https://doi.org/10.5194/egusphere-egu23-12587, 2023.

X4.301
|
EGU23-10978
|
PS4.1
Observations of Clouds on Titan with JWST/NIRCam and Keck/NIRC-2
(withdrawn)
Conor Nixon and the JWST Titan GTO Project Team #1251 and Keck Titan ObservingTeam
X4.302
|
EGU23-8494
|
PS4.1
Scot Rafkin, Audrey Chatain, and Alejandro Soto

Solar and infrared radiative transfer, including the effects of scattering, have been included in the mesoscale Titan WRF (mtWRF) model of Titan’s atmosphere.  A previous study with this model in the absence of radiative forcing indicated that atmosphere-lake sensible and latent heat fluxes could diminish to magnitudes comparable to radiative fluxes due to the development of a cold and stable marine boundary layer.  Consequently, it was hypothesized that radiative forcing could be important, contrary to prior expectations, and should be included in future studies. With these results we confirm the radiative hypothesis and demonstrate that radiative forcing must be included in order to more accurately simulate the energy and mass exchange between Titan’s lakes and atmosphere. Solar heating of the lake mixed layer partially offsets the latent flux cooling during the daytime, and downwelling atmospheric IR flux provides heat to the cold lake.  Due to changes in thermal contrast between the air over the lake and the land compared to non-radiative solutions, the sea breeze atmospheric structure is altered, including the development of a pronounced diurnal circulation cycle.  All of these effects perturb the energy and mass exchange, which has local meteorological implications and exerts a control on the global methane cycle.

How to cite: Rafkin, S., Chatain, A., and Soto, A.: Influence of radiative forcing on Titan’s lake energy balance and sea breeze circulation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8494, https://doi.org/10.5194/egusphere-egu23-8494, 2023.

X4.303
|
EGU23-10653
|
PS4.1
Rania Al Abdallah, Mubarak Almehairbi, Marko Gaseca, and Nayla El-Kork

Mars has changed from a warmer, water-containing planet into a cold and arid environment. Collisions of superthermal oxygen and other atoms with surrounding gases may lead to the escape of light atmospheric molecules, such as D1, OH2, He3, and H24, from the Martian atmosphere. Such processes have probably contributed to the thinning of its atmosphere and the transformation of Mars' climate.

OH molecules can be produced in the Martian atmosphere by the photodissociation of water vapor and in several chemical reactions, such as the reactions of thermal molecular hydrogen and energetic oxygen atoms O + H2 → H + OH 5. Emission and absorption spectra of OH molecules within the Martian atmosphere can lead to a better understanding of these processes. For example, they can help monitor the variation of its abundance with altitude 6. In general, astronomical spectra of specific molecules can be better interpreted through a detailed identification of their line list.

In this work, we present an extensive line list for the B2S+ - X2P and D2S- - X2P electronic transitions of OH, including line intensities, line positions with the relevant quantum numbers of the upper and lower states, e/f parity and oscillator strength, calculated using PGOPHER7 program. The line intensities are found based on calculated ab-initio Transition Dipole Moment Function and potential energy curves obtained using the quantum computational chemistry program MOLPRO8, using CASSCF method followed by MRCI including Davidson correction term (+Q). LEVEL9 program is used to compute Transition Dipole Moment Matrix Elements in Hund's case (b) using the procedure of Numerov-Cooley10 which are then transformed to Hund's case (a) as required by PGOPHER.

 

1 P. Zhang, V. Kharchenko, M. Jamieson, and A. Dalgarno, "Energy Relaxation in Collisions of Hydrogen and Deuterium with Oxygen Atoms," J.  Geophys. Res. 114, A07101 (2009).  

2 M. Gacesa, N. Lewkow, and V. Kharchenko, "Non-thermal escape of molecular hydrogen from Mars," Icarus, L10203 (2012).

3 S. Bovino et al., "Energy Transfer in O Collisions with He Isotopes and Helium Escape from Mars," Geophys. Res. Lett., 38, L02203 (2011).

4 M. Gacesa, P. Zhang, and V. Kharchenko, "Non-thermal escape of molecular hydrogen from Mars," Geophys. Res. Lett., 39, L10203 (2012).

5 M. Gacesa, N. Lewkow and V. Kharchenko, "Non-thermal production and escape of OH from the upper atmosphere of Mars". Icarus, 284, pp.90-96 (2017).

6 S. Raghuram, A. Bhardwaj, & M. Dharwan, “Model for Nitric oxide and its dayglow emission in the Martian upper atmosphere using NGIMS/MAVEN measured neutral and ion densities”. Icarus, 382, 115010 (2022).

7 CM. Western, PGOPHER: a program for simulating rotational, vibrational and electronic spectra. J Quant Spectrosc Radiat Transf., 186:221–42 (2017).

8 HJ. Werner, PJ. Knowles, G. Knizia, FR. Manby, M. Schütz, Molpro: a general purpose quantum chemistry program package. J Chem Phys., 2:242–53 (2011).

9 RJ. LeRoy, "LEVEL: A computer program for solving the radial Schrödinger equation for bound and quasibound levels." J Quant Spectrosc Radiat Transf., 186:167–78 (2017).

10 J. W. Cooley, "An improved eigenvalue corrector formula for solving the Schrödinger equation for central fields," Math. Comput., vol. 15, no. 76, pp. 363–374, (1961).

 

How to cite: Al Abdallah, R., Almehairbi, M., Gaseca, M., and El-Kork, N.: A preliminary investigation of the spectral signatures of excited electronic states of OH in the Martian atmosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10653, https://doi.org/10.5194/egusphere-egu23-10653, 2023.

X4.304
|
EGU23-10685
|
PS4.1
Keith K. C. Chow

Dust activities in the southern high-latitude region around the southern solstice period have been observed in many Martian years. Theses dust events occur near the southern cap-edge region and play a major role in the observed dust climate. However, they generally cannot be simulated in the existing Mars general circulation models. In this report, we will introduce a parameterization scheme for simulating these dust events in the Mars climate model MarsWRF. In this scheme, the dust lifting threshold stress is adjusted with the surface temperature difference between the regolith and ice in the southern polar region. By this approach, dust events in the southern cap-edge region have been simulated around the southern solstice period. As a result, the simulated temperature in the southern high-latitude region is increased and the resulting vertical temperature profile is closer to that from observation. In addition, westward propagating dust events observed in a previous study have been simulated with a propagating speed similar to that observed. Results of numerical experiments suggest that the flow associated with the sublimation of the CO2 ice in the southern cap edge is very important to the occurrence of these dust events in this region.

How to cite: Chow, K. K. C.: Dust Activities in the Southern High-latitudes of Mars, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10685, https://doi.org/10.5194/egusphere-egu23-10685, 2023.

X4.305
|
EGU23-8619
|
PS4.1
Agustín Sánchez-Lavega, Ethan Larsen, Jorge Hernández-Bernal, Teresa del Río-Gaztelurrutia, Iñaki Ordóñez-Etxeberria, and Alejandro Cardesin Moinelo

Four surface stations (rovers Curiosity, Perseverance, and Zhurong, and the Insight platform) were operating on Mars along Martian Year 36 (7 February 2021 – 26 December 2022), all them equipped with a suite of meteorological sensors and cameras. In addition, eight orbiters are currently studying the planet from different perspectives and instruments. To help to interpret and put in context the meteorological measurements at the surface by these stations, we present here a study of the atmospheric disturbances, at the planetary and synoptic scales, based on images of Mars obtained from cameras onboard Mars Express and Mars Reconnaissance Orbiter [1, 2]. We report on the properties of the disturbances that evolved at the edge of the North Polar Cap (latitudes ~ 40°N to 70°N) during the springtime season in the northern hemisphere. These are dust storms and synoptic-scale cloud systems with arc, frontal, irregular and spiral shapes, typically growing from the baroclinic instabilities in the intense eastward jet present in this epoch of the Martian year.  We also report on the evolution of the aphelion cloud belt (Ls ~ 0° – 180°), including among other phenomena the recurrent annular-double cyclone (Ls ~ 125°) and the cloud development at Hellas basin (Ls ~ 145° – 300°). Finally, we present an analysis of the dust storms that evolved at different latitudes, concentrating in particular in the regional storm that evolved over Perseverance in early January 2022.

 

References

[1] Sánchez-Lavega, A. et al., Icarus 299, 194-205 (2018)

[2] Bell III, J. F. et al., J. Geophys. Res. Planets 114, E003315, 1-41 (2009)

How to cite: Sánchez-Lavega, A., Larsen, E., Hernández-Bernal, J., del Río-Gaztelurrutia, T., Ordóñez-Etxeberria, I., and Cardesin Moinelo, A.: Planetary and synoptic-scale atmospheric disturbances from images of Mars during Martian Year 36, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8619, https://doi.org/10.5194/egusphere-egu23-8619, 2023.

X4.306
|
EGU23-2968
|
PS4.1
Gabriele Arnold, Rainer Haus, Joern Helbert, Mario D'Amore, Alessandro Maturilli, Thomas Saeuberlich, and Harald Hiesinger

Analyses of measurements made by MERTIS1 (MErcury Radiometer and Thermal Infrared Spectrometer) during the BepiColombo mission's close flyby 2 of Venus (FB2) have already demonstrated the instrument's capacity to explore the planet's mesosphere at near equatorial latitudes. The MERTIS instrument was designed to study the hot surface of Mercury. It performed well beyond its design limits when analyzing the Venusian mesosphere because of the much lower radiances. MERTIS’ measurements are the first spectrally resolved observations of Venus in the thermal spectral range longward of 5 µm since the Venera-15 Fourier spectrometer experiment in 19832. It could be shown that MERTIS FB2 data enable reliable retrievals of mesospheric temperature profiles and cloud parameters between 60 and 75 km altitude. They are in good agreement with the results of the Venera-15 mission. This indicates the stability of the Venusian atmosphere on time scales of decades3,4.

In this paper we discuss preliminary results from MERTIS measurements of the first flyby (FB1) in October 2020. During the first flyby the spacecraft approached the planet from the solar direction over the dayside. The closest approach (CA) occurred at about 11,000 km distance above the evening terminator of the planet, and then the spacecraft moved away from the planet to the anti-solar direction. In this time the apparent size of Venus increased from slightly larger than one MERTIS pixel (0.7 mrad) to more than 1 degree. MERTIS performed close-up dayside observations from early morning to late afternoon via noon time on Venus at latitudes between 50°S and 85°N and obtained about 785,000 hyperspectral observations with the spectrometer channel. Thus, FB1 observations permit much larger latitude coverage from 50°S to 85°N compared to FB2. To process the FB1 data in terms of both a reasonable signal-to-noise ratio and comparable observing conditions, individual spectra were averaged over 5° latitude belts and 0.5 h local time intervals. We further excluded extreme observation geometries for latitudes northward of 80°N and southward of 40°S as well as very weak spectra. As a result, we are able to generate a reliable data base for use in radiative transfer analyses for the Venusian mesosphere. We present preliminary results on the temperature fields of the mesosphere as a function of local time, altitude, and latitude.

 

Hiesinger, H. et al. Space Sci. Rev. 216, 6 (2020).

Oertel, D. et al. Adv. Space Res. 5, 25-36 (1985).

Arnold, G. et al., SPIE Optic+Photonics, San Diego, Proceedings Volume 12233, doi.org/10.1117/12.2632548 (2022).

Helbert, J. et al. submitted to Nature Astronomy (2023).

How to cite: Arnold, G., Haus, R., Helbert, J., D'Amore, M., Maturilli, A., Saeuberlich, T., and Hiesinger, H.: New insights into the mesosphere of Venus from MERTIS measurements during the two BepiColombo flybys, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2968, https://doi.org/10.5194/egusphere-egu23-2968, 2023.

X4.307
|
EGU23-6164
|
PS4.1
Jean-Yves Chaufray, François Leblanc, Rozenn Robidel, Eric Quémerais, and Dimitra Koutroumpa

Due to the lack of a thick atmosphere, the surface of Mercury is regularly bombarded by micrometeoroids at a rate depending on the position of Mercury around the Sun. One consequence of these impacts is an alteration of its surface (space weathering) and the ejection of its material around Mercury forming a tenuous exosphere. Even if the detail on the origin of the exospheric atomic calcium, observed systematically by MESSENGER is not fully understood, it is mostly associated to such impacts. In order to interpret the MESSENGER observations, we have recently developed a time dependent 3D model of the Ca exosphere of Mercury and successfully reproduced the seasonal variations observed by MESSENGER at dawn during its orbital phase. In this presentation, we will compare the simulated brightness from this model with the observations performed by PHEBUS onboard BepiColombo during the first two flybys of Mercury and discuss the differences.

How to cite: Chaufray, J.-Y., Leblanc, F., Robidel, R., Quémerais, E., and Koutroumpa, D.: Simulation of the Ca emission at Mercury and comparison with the observations by PHEBUS/BepiColombo during the first two flybys, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6164, https://doi.org/10.5194/egusphere-egu23-6164, 2023.

X4.308
|
EGU23-13306
|
PS4.1
John Plane, Thomas Mangan, Anni Määttänen, and Benjamin Murray

Observations show that the temperature above 100 km in Venus’ atmosphere intermittently falls below 100 K, when both H2O and CO2 become supersaturated. Profiles show temperatures can fall below 60 K at heights between 115-125 km, presumably as a result of large amplitude gravity waves.  Cosmic dust particles entering the atmosphere are predicted to ablate between 110 and 125 km. This provides a source of metallic vapours (principally Mg and Fe atoms), which then form metal carbonate molecules known as meteoric smoke particles (MSPs).  Because these molecules are highly polar, they are excellent nuclei for CO2- and H2O-ice particle formation.

In this study we examine the feasibility and kinetics of CO2-ice cloud formation, using both classical nucleation theory (CNT) and bottom-up kinetic nucleation theory (KNT). For CNT, a dimensionless non-isothermal coefficient is included to reduce the nucleation rate of CO2 ice particles, since the atmospheric concentration of the nucleating species (CO2) comprises a significant fraction of the total atmosphere. For heterogeneous CNT on MSPs, a surface diffusion approach is used where molecules can diffuse on the surface to form a critical cluster for nucleation and the effect of dissipation of critical clusters is accounted for. Application of CNT shows that whereas homogeneous nucleation should be too slow for significant cloud formation, heterogeneous nucleation rates around 1 cm-3 s-1 for CO2 ice should be possible in the colder regions (< 80 K).

For KNT, the rate coefficients for the sequential addition of CO2 molecules up to MgCO3(CO2)40 were calculated explicitly with Rice Ramsperger Kassel Markus (RRKM) theory, using a solution of the Master Equation based on the inverse Laplace transform method. The rates of dissociation of the clusters i.e. MgCO3(CO2)n+1 → MgCO3(CO2)n + CO2, were calculated by detailed balance. In order to explore the evolution of the CO2-ice clouds, a 1-dimensional model was constructed to describe the nucleation, growth, sedimentation and sublimation of the ice particles. The model is initiated with a vertical profile of atmospheric density and temperature determined using the Solar Occultation in the InfraRed (SOIR) instrument on a specified orbit of Venus Express, and then follows the fate of an MSP seed particle as it grows, sediments and finally sublimates on entering a warmer region. Two categories of cloud tend to be produced from the observed temperature profiles. The first peaks around 120 km with particles around 100-200 nm radius; and the second type persists for longer and peaks around 110 km, with particles that can exceed 2 μm in radius. Most clouds are predicted to occur at high latitudes (>70o). Using a probable underestimate of the MSP concentration (100 cm-3), the optical extinction of these clouds at 220 nm should be readily observable by the SOIR instrument. However, the clouds are short-lived because of rapid sedimentation (typically 300 s, the longest-lived around 1200 s), so that the detection of these ephemeral “hail showers” will be challenging.

How to cite: Plane, J., Mangan, T., Määttänen, A., and Murray, B.: Ephemeral carbon dioxide ice clouds in the upper mesosphere of Venus, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13306, https://doi.org/10.5194/egusphere-egu23-13306, 2023.

Posters virtual: Thu, 27 Apr, 16:15–18:00 | vHall ST/PS

Chairpersons: Quentin Nenon, André Galli
vSP.27
|
EGU23-13614
|
PS4.1
Emiliano D'Aversa, Giuseppe Sindoni, Fabrizio Oliva, Manuel Lopez Puertas, Gabriella Gilli, Christina Plainaki, Federico Tosi, Giuseppe Piccioni, Gianrico Filacchione, François Poulet, Yves Langevin, Nicolas Ligier, John Carter, Alessandra Migliorini, Francesca Altieri, Davide Grassi, and Paolo Haffoud

The most direct evidence that the icy Galilean satellite Callisto is able to sustain a significant neutral exosphere dates back to the detection of the CO2 non-LTE emission at 4.3 μm wavelength, measured by the NIMS instrument onboard the NASA Galileo spacecraft [1]. Other exospheric emissions have been observed in the UV spectral range, basically tracing the ionised exospheric component ([2], [3]). The analysis of such emissions in the framework of exospheric models (see e.g. [4], [5]) allowed to establish an overall composition dominated by O2 and H2O, with minor contributions by CO2 and CO. However, direct observations of neutral species other than CO2 are still missing, and their actual abundances, as well as spatial and temporal variability, are poorly constrained.

The MAJIS (Moon And Jupiter Imaging Spectrometer, [6]) instrument, on board the ESA JUICE spacecraft, is expected to contribute in this field, by searching for non-LTE emissions falling in its spectral range, from 0.50 to 5.54 μm. In particular, we evaluate the chance of detection of signals at the satellite’s limb emitted by the CO2 complexes at 4.3 μm and 2.3 μm, by the H2O complex at 2.3 μm, by O2 at 1.27 μm, and by the CO bands at 4.7 μm and 2.3 μm. We calculate the populations of molecular levels by using the GRANADA algorithm [7], then the emissions intensities, for reference abundances of the molecular species and for limb-viewing geometry, by taking advantage of the KOPRA algorithm [8].

Detection limits for all the abovementioned species are obtained in the approximation of horizontal uniformity of exospheric layers and adopting a vertical scaling compatible with the scale height in [1]. Surface density detection limits around 6.2 .106 cm-3, 6.6 .106 cm-3, 3.4 .109 cm-3, 3.4 .107 cm-3 are found for CO2, H2O, O2, and CO respectively. For both CO2 and H2O, these results indicate a high detection probability during the Callisto flybys planned in the current JUICE trajectory version (crema 5.0, [9]). Detection of O2 could also be possible if appropriate observing strategies are adopted. Detection of CO is instead very challenging, being its expected abundance well below the detection limit.

 Acknowledgements

This work is supported by the Italian Space Agency (ASI-INAF grant 2018-25-HH.0). IAA researchers acknowledge financial support from the State Agency for Research of the Spanish MCIU through the Center of Excellence Severo Ochoa" award to the Instituto de Astrofísica de Andalucía (CEX2021-001131-S/fund by MICIN/AEI/10.13039/501100011033).

References

[1] Carlson,R.W.,1999, Science 283 (5403): 820–21. [2] Kliore,A.J., 2002, Journ.Geophys.Res. doi: 10.1029/2002ja009365. [3] Cunningham,N.J. et al., 2015, Icarus. doi:10.1016/j.icarus.2015.03.021. [4] Vorburger,A., et al., 2015, Icarus. doi:10.1016/j.icarus.2015.07.035. [5] Liang, M., 2005, Journ.Geophys.Res. doi:10.1029/2004je002322. [6] Guerri I., et al., 2018, Proc.of SPIE Vol.10690 106901L-1. doi: 10.1117/12.2312013. [7] Funke,B., et al., 2012, Journ.Quant.Sp.Rad.Tran. doi:10.1016/j.jqsrt.2012.05.001. [8] Stiller,G.P., et al., 2002. Journ.Quant.Sp.Rad.Tran. doi:10.1016/s0022-4073(01)00123-6. [9] ESA SPICE Service, JUICE Operational SPICE Kernel Dataset, doi:10.5270/esa-ybmj68p.

How to cite: D'Aversa, E., Sindoni, G., Oliva, F., Lopez Puertas, M., Gilli, G., Plainaki, C., Tosi, F., Piccioni, G., Filacchione, G., Poulet, F., Langevin, Y., Ligier, N., Carter, J., Migliorini, A., Altieri, F., Grassi, D., and Haffoud, P.: Observability of Callisto’s exosphere with MAJIS/JUICE, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13614, https://doi.org/10.5194/egusphere-egu23-13614, 2023.

vSP.28
|
EGU23-2921
|
PS4.1
|
Andrew Jordan and Morgan MacLeod

A number of studies have suggested that dielectric breakdown weathering (“sparking”) may occur on airless bodies in the Solar System. To experience dielectric breakdown, a regolith must be exposed to a sufficiently high fluence of energetic charged particles (>1010 cm-2), and this fluence must be deposited on a timescale less than the regolith’s discharging timescale, which increases with decreasing temperature. Consequently, dielectric breakdown occurs in regolith that is both cold and exposed to high fluxes of solar energetic particles (SEPs) or radiation belt particles. If breakdown occurs, then it causes space weathering by melting and vaporizing microscopic channels through regolith near the surface.

We describe our recent experimental, observational, and theoretical work investigating where dielectric breakdown may be an important space weathering process. In the inner Solar System, airless bodies are exposed sporadically to SEP events with high fluences. At 1 AU, the flux of SEPs is nearly isotropic, and thus they may cause dielectric breakdown over the coldest (<120 K) regions of the Moon’s nightside. We present observational evidence for this nightside process and the results of preliminary experiments investigating its microscopic effects. In addition, we briefly discuss the possibility that dielectric breakdown weathering also occurs on Mercury, the moons of Mars, and some asteroids.

In the outer Solar System, where the fluxes of SEP events are significantly reduced, dielectric breakdown is more likely to be caused by radiation belts. In particular, moons in Jupiter’s radiation belts are exposed to the highest continuous fluxes of energetic charged particles in the Solar System. Furthermore, Jupiter’s radiation belts have caused dielectric breakdown in spacecraft dielectrics. We describe the range of evidence showing that dielectric breakdown may occur on some of the Galilean moons (Io, Europa, and Ganymede) and Jupiter’s four innermost moons (Amalthea, Thebe, Adrastea, and Metis).

How to cite: Jordan, A. and MacLeod, M.: Airless body surface weathering by dielectric breakdown, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2921, https://doi.org/10.5194/egusphere-egu23-2921, 2023.