Monday 30/01
ISSI introduction Mark Sargent
Exosphere
Introduction François Leblanc
« Physics in Exosphere Generation » Audrey Vorburger
In this presentation I would like to give an overview of our current understanding of the physical processes that govern exospheres, with a special highlight on open questions. In particular, I would like to go into detail about thermal release, micrometeorite impact vaporization, photon-stimulated desorption, electron-stimulated desorption, and ion sputtering, and how the are similar / different at the Moon and Mercury.
“Exospheric modelling: a plethora of assumptions” Dana Hurley
In it I can describe my model and how it works. But then go into detail on the assumptions that go into the model and the consequences of those assumptions.
“Diurnal variability of exospheres: what is still missing?” François Leblanc
I will present the modelling of the Na exosphere at Mercury and Ne exosphere at the Moon and discuss the discrepancies between simulation results and observations.
“How regolith shapes gas retention and emission” Menelaos Sarantos
Performing ray tracing in grain piles that approximate the structure of regolith, new insights are obtained about how to improve our assumptions for global exosphere simulations
Tuesday 31/01
“An Analytical approach for the yearly variability of the Sodium exosphere of Mercury” Alessandro Mura
Regolith
Introduction Menelaos Sarantos
“Geochemical Effects on the Solar Wind-Induced Lunar Water Cycle » Alexander Smolka
I will present my own simulation tool and my latest results for hydrogen-based species of the lunar exosphere as well as our current status of the research on geochemical conversion reactions. The main goal is to link these conversion reactions with the exosphere simulation to include important effects like inter-species dependencies and desorbtion lags in the prediction of the lunar water cycle.
« Modeling Collisional Sources and Rough Surfaces on the Moon and Mercury » Prem Parvathy
Situations where modeling intermolecular collisions and gas opacity becomes important; modeling small-scale horizontal and vertical temperature variations; preparations for comparing model results to future measurements at the lunar surface.
Wednesday 01/02
“Heat and mass transfer in lunar regolith to predict migration and release of water” Philipp Reiss
I will introduce the combined model we have developed over the past years to simulate heat and mass transfer in regolith on a microphysical scale. The model was applied to predict the release of volatile species from lunar regolith in support of instrument development (in-situ thermal processing and evolved gas analysis). It was also applied to predict migration of water over depth via passive thermal pumping. I will present this recent work (both simulation and experiments) together with an outlook of potential future studies as a basis for discussion on how this subsurface regolith model can be useful to improve the surface-exosphere interface.
“Effects of the Lunar Regolith Structure and of the Solar Wind Properties on the Backscattered Energetic Neutral Atoms Flux” Sébastien Verkercke
The backscattered Energetic Neutral Atoms (ENA) flux from the Moon surface is believed to be influenced by both the regolith structure and the solar wind conditions. The actual large range of reflection coefficients (~0.1 – 0.2) 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. 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.
Laboratory experiments
« Solar wind sputtering and thermal desorption of metal volatiles from Mercury regolith analogs » Adam Woodson
I’ll present sputter-depletion cross sections for sodium vapor deposited on synthetic forsterite (Mg2SiO4) targets of different grain size fractions (~50 um to 500 um) and irradiated with 4 keV He+. These will be compared with cross sections derived from ray-tracing simulations that incorporate 3D height maps of the experimental targets and angular/energy distributions obtained from SDTrimSP.
Sputtering (4 keV He+) cross sections for vapor-deposited potassium removed from magnesium-bearing ilmenite [nominally (Fe, Mg,Ti)O3] sections have been obtained as a function of temperature (110–400K) as well and will be presented for discussion and comment.
I’ll also discuss plans for further measurements using additional volatiles (e.g. Na, K, Ca, Mg, Al, Fe, Mn) and regolith analogs (e.g. feldspars, FeS, MgS, CaS, meteorites, lunar soil) pertinent to Mercury’s exospheric and surface-mineralogical compositions. Team input welcomed!
Other topics of interest: 1) strategies for characterizing surface “roughness” (e.g. Surface Inclination Angle Distribution (SIAD)? something better?) and parameterizing sputter/desorption cross sections and angular/energy distributions in terms of roughness parameters (e.g. model parameters obtained from fits to SIAD) 2) strategies for global simulation of the coupling between regolith topography/mineralogy and the radiation environment (e.g. a realistic/portable/computationally-fast statistical model of surface topography/mineralogy useful for global exosphere simulations) 3) simulation and measurement of Na and K diffusion through, across, and between regolith grains
Thursday 02/02
« Recent laboratory experiments for planetary surfaces interacting with their space environment »Andre Galli
The emphasis will be on sputtering experiments with H+, He++ and heavy ions irradiating mineral films and porous regolith samples. I will also briefly review the status of experiments dealing with electron-desorption, photodesorption, and thermal desorption relevant for the surfaces of Mercury and the Moon. The paper by Wurz et al. 2022
(https://doi.org/10.1007/s11214-022-00875-6) will serve as a reference and I will concentrate on the developments over the last three years since our previous ISSI workshop “Surface Bounded Exospheres and Interactions in the Solar System”. A guiding question for our discussions might be if the 1:1 simulation of space weathering in laboratory conditions is both achievable and worthwhile.
”Surface interaction driven exospheric structure and dynamics at planetary bodies” Ben Teolis
Synthesis
Synthesis of each topic and discussion (leaders of each topic) François Leblanc, Menealos Sarantos, André Galli
Friday 03/02