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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.

The repeated eruptions of water plumes on Europa have been suggested based on Hubble observations, Keck observations and in-situ magnetic field data from Galileo (Roth et al., 2014; Sparks et al., 2016, 2017, 2019; Jia et al., 2018; Arnold et al., 2019; Paganini et al., 2019). The possibility that such plumes could transport material from Europa’s subsurface, or from water reservoirs contained in the ice layer (Vorbuger and Wurz 2021), far above the surface creates an unprecedented opportunity to sample Europa’s subsurface environment and investigate its habitability. The JUpiter ICy moon Explorer (JUICE) is scheduled to make two flybys of Europa, one over the Northern and one over the Southern hemisphere, with the closest approach at 400 km altitude.In this work we investigate the detectability of such water plumes using the Neutral and Ion Mass Spectrometer (NIM) and the ion mass spectrometer Jovian Dynamics and Composition analyser (JDC) of the Particle Environment Package (PEP) on JUICE. Using a Monte Carlo particle tracing model we simulate the density distribution of the plume and simulate the measured signature with NIM and JDC along the two JUICE flyby trajectories.Using a particle tracing model we show that H2O molecules and H2O+ ions of the plume, as well as possible minor constituents such as CO and CH4, can be detected during the JUICE flybys. We find that the plume reported by Roth et al., 2014 is the most likely to be detected, even at the lowest mass fluxes, and that the southern-hemisphere JUICE flyby has the best coverage of all the presumptive plume sources. Lowering the altitude of the southern flyby will contribute to an increased chance of detecting the presumptive plume sources, and should be prioritized over lowering the other flybys if any deltaV is available.Additionally, using a DSMC molecule and particle tracing model we investigate the effect of intermolecular collisions in the plume and demonstrate that such collisions will reduce the detectability of the plume. We also show that the JUICE flybys and the NIM characteristics will be suitable to discern the finer structure of the plume (e.g. shocks inside the plume), which will allow us to improve our understanding of the physics of Europa’s plumes.Furthermore, we also investigate the separability of the plume from Europa’s asymmetric sputtered and sublimated water atmosphere and discuss the influence of the instrument pointing and operations on the plume detectability. We find that NIM’s operational constraints are not critical in terms of detecting H2O molecules of a plume.

Among Jupiter's satellites, Ganymede undoubtedly has one of the most complex atmospheres. This is primarily due to the fact that Ganymede has its own magnetic field, which forms a small magnetosphere within the much larger magnetosphere of Jupiter. This interaction not only results in atmospheric auroral emissions in the UV range but also strongly influences Ganymede’s space environment.With the recent Ganymede flyby by the Juno spacecraft, new information on Ganymede’s environment has become available. We have included these measurements into our 3D Monte Carlo model, determining Ganymede’s resulting H2O, O2, H2, O, and H atmosphere. Our simulations show that accounting for all major source and loss processes, sublimation is still the dominating source process for the water in Ganymede’s atmosphere, delivering more than three orders of magnitude more molecules to the atmosphere than all other source processes combined. For the non-condensing atmospheric species (O2 and H2), on the other hand, it is the auroral electrons that mainly govern the atmospheric structure and density. The auroral electrons also govern the structure and density of the atomic species O and H, which are mainly added to the atmosphere by electron-impact dissociation of O2 and H2 in the auroral belts. Comparison with available spectroscopic observations of Ganymede’s atmospheric constituents shows that our results agree well with the results inferred from these observations, with the exception of H, where our derived line-of-sight column density is about one order of magnitude lower than the column density inferred from Lyman-α measurements.Our analysis shows that for a complete understanding of Ganymede's atmosphere, simultaneous observations of Ganymede's surface, atmosphere, and plasma environment at different times and locations are particularly important. Such measurements are planned with the Jupiter ICy moons Explorer, in particular with the Particle Environment Package (PEP). In this presentation we will show how PEP will help us learn more about Ganymede’s complex atmosphere, providing simultaneous in-situ electron, ion, and neutral gas measurements.

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 neutraland plasma torus. SERPENS is designed to eject particles via sputtering and thermal evaporation atregular time intervals allowing us to simulate an evolving cloud/torus. Multiple species including Na, Kand 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.

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.

The Mars Ion and Neutral Particle Analyzer (MINPA), one of the three scientific payloads onboard the Tianwen-1 orbiter, was designed to measure ions and energetic neutral atoms (ENAs) at Mars. From November 2021, MINPA started to collect scientific data around Mars. Here, we present MINPA's first results of the solar-wind ENAs, which are produced through the charge exchange process between the solar wind hydrogen ions and the Martian neutral exosphere. We perform a comprehensive comparison between the inflight ENA data and ground calibration results to understand the energy and angular distributions of the solar-wind ENA signals. The possible contamination of these observations by ions and solar extreme ultraviolet (EUV) is evaluated by comparing the ENA measurements with the ion data. We will present several cases of the solar wind ENA observations, and their intensities are estimated to be 10^5~10^6 cm^-2 sr^-1 s^-1, which is in good agreement with previous in situ measurements and predictions using models.

Imaging space plasmas via Energetic Neutral Atoms (ENA) is a widely used technique to study space plasma population ranging from the Earth’s magnetosphere all the way to the interstellar medium. Laboratory calibration against a known ENA beam source is a key element in the development and testing of spaceborne ENA imaging instruments. For ENA instruments operating at energies below about 1 keV, an ion beam source cannot be used for the instrument calibration, as ion trajectories are distorted through electromagnetic fields inside the ENA instrument whereas neutrals are not. The MEFISTO laboratory test facility at the University of Bern is well suited to carry out such ENA instrument calibrations: It provides neutral atom beams of any species from H to heavy elements at the relevant low-energy range from 3 keV down to 10 eV. MEFISTO is equipped with a large vacuum test chamber and an electron-cyclotron resonance ion source (ECRIS) for the production of a primary ion beam. Ion beam neutralization is performed with a dedicated neutralization stage via grazing scattering surface neutralization. This neutralization method introduces some uncertainty to the neutral beam energy and comes with species and energy dependent throughput.Therefore, neutral beam calibrations have been conducted against a novel Absolute Beam Monitor (ABM), which serves as a primary calibration standard in the low-energy ENA range. Calibrated neutral beam fluxes and energies have been obtained for species of interest to interstellar, heliosphere and planetary science, including H, D, He, O, Ne neutral beams. The recently upgraded 5-axis movable hexapod table in the test chamber allows for precise motion and rotation of instrument under test relative to ENA calibration beam. These measures allow us to carry out thorough ENA instrument calibrations against a well-characterized low-energy neutral atoms beam source.

Scientific detection and imaging instruments for low-energetic neutral atoms (ENA) onboard spacecraft require thorough pre-flight laboratory calibration against a well-characterized neutral atom beam source. To achieve this requirement, a dedicated test facility is available at the University of Bern, which is equipped with a powerful plasma ion source and an ion beam neutralization stage. Using surface neutralization, low-energy neutral atom beams of any desired gas species can be produced in the energy range from 3 keV down as low as 10 eV. As the efficiency of the neutralization stage is species and energy dependent, the neutralizer itself needs to be calibrated against an independent reference. We report on the calibration and characterization of this neutral atom beam source using our recently developed Absolute Beam Monitor (ABM) as a primary calibration standard. The ABM measures the absolute ENA flux independent of neutral species in the energy range from 10 eV to 3 keV. We obtain calibration factors of a few 100 cm−2 s−1 pA−1, depending on species at beam energies above about 100 eV, and a power-law decrease for energies below 100 eV. Furthermore, the energy loss of neutralized ions in the surface neutralizer is estimated from time-of-flight measurements using the ABM. The relative energy loss increases with ENA energy from low levels near zero up to 20%–35% at 3 keV, depending on atomic species. Having calibrated our neutral beam source allows for accurate calibration of ENA space instruments.

Rocky bodies in space without a protective atmosphere like Mercury are subject to harsh conditions, including the bombardment by solar wind ions. This leads to the ejection of particles along with alteration of the surface properties like composition and morphology. These ion-induced sputter processes contribute to the formation of the Hermean exosphere [1]. Therefore, understanding the involved fundamental ion-solid interaction processes is important for the modelling of exosphere creation. From a computational standpoint, those impacts are usually investigated using simulation codes based on the Binary Collision Approximation (BCA) like SRIM [2] or SDTrimSP [3]. However, past studies revealed that especially for compound targets relevant as Hermean regolith analogues, simulations have to be adapted by means of modified input parameters to reproduce experimental results [4]. Thus, laboratory measurements are strongly needed to ensure that valid inputs enter the exosphere modelling. A well-proven method for such investigations of sputtering is the Quartz Crystal Microbalance (QCM). It allows to measure sputter yields of thin films deposited onto a quartz resonator with high precision in real time and in situ [5]. Expanding on this technique, we use a setup in which we place a second QCM in the vicinity of the irradiated target, facing the centre of particle emission [6]. Ejecta that stick to its surface result in a mass accumulation, which is resolved through the piezoelectric properties of the quartz resonator. By moving this second catcher-QCM in an arc around the target, the angular emission characteristic of sputtered particles can be probed. The experimental realisation is sketched in figure 1. The setup also allows for experiments with targets that cannot be deposited onto a resonator or whose surface properties change during the deposition process. Particularly, the above-mentioned films used in, e.g. [4], are vitreous and smooth. We therefore extended our studies to pellets from ground and pressed mineral specimens that retain some roughness for a more realistic regolith analogue [7]. Through comparison of these measured angular distributions with reference samples, also total sputter yields can be determined for targets whose yields cannot be measured with a single QCM. Figure 1: Sketch of the setup. A target is irradiated with an ion beam under an angle of incidence α. The angular distribution of ejecta (blue shaded area) is probed with the catcher-QCM by varying the angle αC. We initially used a 2 keV Ar+ ion beam to irradiate both an enstatite (MgSiO3) film and a pellet under 60° and 45° incidence with respect to the sample surface normal. This choice of projectile has a high sputter yield and produces sufficient signal at the catcher-QCM to allow for a proof of principle. After initial hardships, modified sample preparation routines made reproducible quantification of the obtained data possible. We attribute differences in shape and magnitude of the sputtered particle angular distributions between the sample types to the different roughnesses of the sample configurations. Geometric considerations alone are sufficient to describe the qualitative behaviour of our results [8]. Simulation results to visualise the impact of surface roughness on the sputter yield as a function of incidence angle are given in figure 2. For a solar wind relevant projectile species, the same measurements were also carried out with a 4 keV He+ ion beam. This presentation will include the results from both the He and the Ar irradiation experiments. Figure 2: Sputter yields Y for a perfectly smooth surface (as simulated by SDTrimSP, blue) and for the surface of an enstatite (MgSiO3) pellet used in this study in orange. The latter are obtained using a home-made code based on geometric considerations [8]. References [1] P. Wurz et al.: Planet. Space Sci. 58, 1599, 2010 [2] J.F. Ziegler et al.: Nucl. Instrum. Methods Phys. Res. B: Beam Interact. Mater. At., 268, 1818, 2010 [3] A. Mutzke et al.: SDTrimSP Version 6.00. Max-Planck-Institut für Plasmaphysik, 2019 [4] P.S. Szabo et al.: Astrophys. J., 891, 100, 2020 [5] G. Hayderer et al.: Rev. Sci. Instrum., 70, 3696, 1999 [6] H. Biber et al.: EPSC2021, online, EPSC2021-526, 2021 [7] N. Jäggi et al.: Icarus, 365, 114492, 2021[8] C. Cupak et al.: Appl. Surf. Sci., 570, 151204, 2021

The repeated eruptions of water plumes on Europa have been suggested based on Hubble observations, Keck observations and in-situ magnetic field data from Galileo (Roth et al., 2014; Sparks et al., 2016, 2017, 2019; Jia et al., 2018; Arnold et al., 2019; Paganini et al., 2019). The possibility that such plumes could transport material from Europa’s subsurface, or from water reservoirs contained in the ice layer (Vorbuger and Wurz 2021), creates an unprecedented opportunity to sample Europa’s subsurface environment and investigate its habitability. The JUpiter ICy moon Explorer (JUICE) is scheduled to make two flybys of Europa, one over the Northern and one over the Southern hemisphere, with the closest approach at 400 km altitude.In this work we investigate the detectability of such water plumes using the Neutral Mass Spectrometer (NIM) and the ion mass spectrometer Jovian Dynamics and Composition analyser (JDC) of the Particle Environment Package (PEP) on JUICE. Using a Monte Carlo particle tracing model we simulate the density distribution of the plume and simulate the measured signature with NIM and JDC along the two JUICE flyby trajectories.We show that H2O molecules and H2O+ ions of the plume can be detected during the JUICE flybys. We also investigate the detectability of the plume source as a function of location on the surface of Europa and as a function of the plume mass flux. We find that the plume reported by Roth et al., 2014 is the most likely to be detected, even at the lowest mass fluxes, and that the first JUICE flyby has the best coverage of all the presumptive plume sources. Using a DSMC simulation of the plume we comment on the effect of intermolecular collisions in the plume and demonstrate that such collisions will reduce the detectability of the plume.Lowering the altitude of this flyby will contribute to an increased chance of detecting the presumptive plume sources, and should be prioritized over lowering the other flybys if any deltaV is available. Furthermore, we also investigate the separability of the plume from Europa’s asymmetric water atmosphere and discuss the influence of the instrument pointing and operations on the plume detectability.

Ganymede’s water exosphere has been observed spectroscopically on several occasions since the first detection of atomic hydrogen in Ganymede’s exosphere in 1997 [1]. From these observations a consistent picture of Ganymede’s exosphere has emerged: Ganymede’s day-side exosphere is dominated by sublimated water with inferred column densities of up to several 1e15 cm-2, while elsewhere the exosphere is dominated by sputtered molecular oxygen (inferred column densities of several 1e14 cm-2) at low altitudes and by atomic oxygen (inferred column densities of several 1e13 cm-2) at higher altitudes [2-9]. In addition, atomic hydrogen has been observed with inferred column densities of a few 1e12 cm-2 [1, 4, 10]. Whereas many modeling approaches have been able to reproduce the inferred H2O and O2 densities, they have struggled to re-create the high inferred atomic oxygen and hydrogen column densities [11-13]. In this work, we present new simulations of Ganymede’s water-related exosphere. Our modeling results reproduce the observed H2O emissions well by sublimating water at Ganymede’s day-side surface temperature. The observed OI emission lines, which were interpreted as an O2 atmosphere, on the other hand, agree with a sputter source, with Jupiter’s magnetospheric plasma acting as the sputter agent. Ganymede has a complex magnetic field, that shields part of the surface (mainly the equatorial regions) from impinging plasma ions and electrons, leaves the polar caps exposed to unhindered plasma precipitation, and accelerates the precipitating plasma in the separatrix, resulting in strong auroral emissions [2-8]. We show that the thermal electrons reaching the polar caps are insufficient to produce the amount of atomic oxygen and hydrogen inferred from the observations, and that an interaction between the water atmosphere and auroral electrons is necessary. In addition, we will discuss how the Particle Environment Package [14] onboard ESA’s JUpiter and ICy moons Explorer [15] will help us learn more about Ganymede’s atmosphere and plasma environment. [1] Barth, C. A., C. W. Hord, A. I. F. Stewart, W. R. Pryor, K. E. Simmons, W. E. McClintock, J. M. Ajello, K. L. Naviaux, and J. J. Aiello (1997), “Galileo ultraviolet spectrometer observations of atomic hydrogen in the atmosphere of Ganymede”, Geophysical Research Letter, 24(17), 2147–2150. [2] Hall, D. T., P. D. Feldman, M. A. McGrath, and D. F. Strobel (1998), “The Far-Ultraviolet Oxygen Airglow of Europa and Ganymede”, The Astrophysica Journal, 499(1), 475–481. [3] Brown, M. E., and A. H. Bouchez (1999), “Observations of Ganymede’s visible aurorae”., in Bulletin of the American Astronomical Society, vol. 31. [4] Feldman, P. D., M. A. McGrath, D. F. Strobel, H. W. Moos, K. D. Retherford, and B. C. Wolven (2000), “HST/STIS Ultraviolet Imaging of Polar Aurora on Ganymede”, The Astrophysical Journal, 535(2). [5] McGrath, M. A., X. Jia, K. Retherford, P. D. Feldman, D. F. Strobel, and J. Saur (2013), “Aurora on Ganymede”, Journal of Geophysical Research (Space Physics), 118(5), 2043–2054. [6] Saur, J., S. Duling, L. Roth, X. Jia, D. F. Strobel, P. D. Feldman, U. R. Christensen, K. D. Retherford, M. A. McGrath, F. Musacchio, A. Wennmacher, F. M. Neubauer, S. Simon, and O. Hartkorn (2015), “The search for a subsurface ocean in Ganymede with Hubble Space Telescope observations of its auroral ovals”, Journal of Geophysical Research (Space Physics), 120(3). [7] Musacchio, F., J. Saur, L. Roth, K. D. Retherford, M. A. McGrath, P. D. Feldman, and D. F. Strobel (2017), “Morphology of Ganymede’s FUV auroral ovals”, Journal of Geophysical Research (Space Physics), 122(3). [8] Molyneux, P. M., J. D. Nichols, N. P. Bannister, E. J. Bunce, J. T. Clarke, S. W. H. Cowley, J. C. Gérard, D. Grodent, S. E. Milan, and C. Paty (2018), “Hubble Space Telescope Observations of Variations in Ganymede’s Oxygen Atmosphere and Aurora”, Journal of Geophysical Research (Space Physics), 123(5). [9] Roth, L., N. Ivchenko, G. R. Gladstone, J. Saur, D. Grodent, B. Bonfond, P. M. Molyneux, and K. D. Retherford (2021), “Evidence for a sublimated water atmosphere on Ganymede from Hubble Space Telescope observations”, Nature Astronomy, 5. [10] Alday, J., L. Roth, N. Ivchenko, K. D. Retherford, T. M. Becker, P. Molyneux, and J. Saur (2017), “New constraints on Ganymede’s hydrogen corona: Analysis of Lyman-α emissions observed by HST/STIS between 1998 and 2014”, Planetary and Space Science, 148. [11] Marconi, M. (2007), A kinetic model of ganymede’s atmosphere, Icarus, 190(1). [12] Turc, L., L. Leclercq, F. Leblanc, R. Modolo, and J.-Y. Chaufray (2014), Modelling ganymede’s neutral environment: A 3d test-particle simulation, Icarus, 229. [13] Leblanc, F., A. Oza, L. Leclercq, C. Schmidt, T. Cassidy, R. Modolo, J. Chaufray, and R. Johnson (2017), On the orbital variability of ganymede’s atmosphere, Icarus, 293. [14] Barabash, S., Wurz, P., Brandt, P., Wieser, M., Holmström, M., Futaana, Y., et al. (2013). “Particle Environment Package (PEP)”, European Planetary Science Congress 2013. [15] Grasset, O., Dougherty, M. K., Coustenis, A., Bunce, E. J., Erd, C., Titov, D., et al. (2013). “JUpiter ICy moons Explorer (JUICE): An ESA mission to orbit Ganymede and to characterise the Jupiter system”. Planetary and Space Science, 78, 1–21.

Figure 1, left: Ions interacting with the Moon cause a multitude of phenomena that influence its surface as well as its environment. Right: An example for a regolith setup used for SDTrimSP-3D simulations. Ions from the solar wind and the Earth’s magnetosphere continuously impact the Moon [1, 2], which affects its surface and its particle environment (see Fig. 1). Due to the complex granular structure of the lunar regolith, an exact understanding of its interaction with precipitating ions is challenging. A better description of the occurring effects is essential for improving models of space weathering and exosphere formation. Important insights have been provided by the analysis of solar wind protons that are scattered as energetic neutral atoms (ENAs) [3-5]. Several observed characteristics are potentially linked to the regolith morphology, but a detailed description of the occurring processes is still lacking. To answer open questions on the interaction of ions with the lunar regolith, we have implemented a regolith grain model in the ion-solid interaction code SDTrimSP-3D [6]. This simulation program sequentially traces all scattering events between atoms that are set into motion by an impacting ion. Grain shapes with varying fractal dimensions can be realized using a spherical harmonics expansion [7], with an example for a regolith setup being shown in the right image of Fig. 1. Figure 2, left: Chandrayaan-1 observations of the reflection coefficient (from [8]) are well reproduced by the regolith simulations with SDTrimSP-3D. Right: Sputter yields from regolith are also predicted to have a strongly decreased angular dependence. Using the above-described inputs, simulations of the reflection coefficient and sputtering yields of solar wind protons impacting an enstatite (MgSiO3) regolith were performed. As shown in Fig. 2, both reflection and sputtering are found to be much less dependent on the angle of incidence compared to a flat surface. Overall, the ENA reflection coefficients from Chandrayaan-1 [8] can be very well reproduced with the regolith simulations. Lower ENA emission energies as well as a preferential backwards scattering as measured by Chandrayaan-1 [9,10] are also observed in SDTrimSP-3D. The major results of these spacecraft measurements can thus be connected to the granular regolith morphology. Therefore, the SDTrimSP-3D regolith simulations represent an important step towards an improved description of space weathering and the particle environment of the Moon. References [1] A.R. Poppe, W.M. Farrell, J.S. Halekas, J. Geophys. Res.: Planets, 123 (2018), 37. [2] Q. Nénon, A.R. Poppe, Planet. Sci. J., 1 (2020), 69. [3] M. Wieser, et al., Planet. Space Sci. 57 (2009), 2132. [4] D.J. McComas, et al., Geophys. Res. Lett. 36.12 (2009). [5] A. Zhang, et al., Planet. Space Sci. 189 (2020), 104970. [6] U. von Toussaint, A. Mutzke, A. Manhard, Phys. Scripta T170 (2017), 014056. [7] D. Wei, et al., Comp. Geotech. 104 (2018), 1. [8] A. Vorburger, et al., J. Geophys. Res.: Space Phys. 118.7 (2013), 3937. [9] Y. Futaana, et al., J. Geophys. Res.: Planets 117 (2012), E05005. [10] A. Schaufelberger, et al., Geophys. Res. Lett. 38.22 (2011).

Surface sputtering, the process of energetic ions (e.g. from the solar wind) ejecting particles from the surface, is one of the major processes to supply energetic particles to a thin, collisionless atmosphere on otherwise atmosphere-free celestial bodies. The energetic ejecta reach high altitudes or may escape the celestial body completely so they can be observed remotely from the ground or in-situ with a spacecraft. The accuracy of a model to reproduce the thin atmosphere surrounding exposed rocky bodies such as the Moon and Mercury therefore requires accurate sputter efficiencies. Determining the sputter yields of the various species from a realistic mineral surface is still a work in progress [1]. Modeling of sputtering with commonly used Binary Collision Approximation (BCA) models such as TRIM [2] has been shown to overestimate the sputter yields compared to experimental data [3, 4]. The number of sputter experiments performed on rock forming minerals is growing steadily, however. We apply the latest results to obtain yields for a range of minerals from the state-of-the-art code SDTrimSP [5], which is an improved model based on the static TRIM and the dynamic TRIDYN [6]. We present a novel implementation of oxides as components to appropriatly represent mineral densities in SDTrimSP by distinguishing between bound and free O atoms in the simulation. We compare the oxide implementation to recent sputter yields obtained from mineral pellets and mineral-derived thin-film irradiation experiments [2,3,4]. One of our preliminary results is shown in Figure 1 where we compare the SDTrimSP sputter yields of the commonly used atomic model and the newly implemented oxide model with experimental data from [4]. For reference we also show the atomic model equivalent results from the widely used SRIM code. This work includes a parameter study including density, binding energy, and binding model and how they affect the resulting mineral sputter yields as well as the ejectas energy and angular distribution. We further elaborate on necessary experiments to better constrain the parameter spaces. Figure 1: Sputter yields of solar wind energy hydrogen ions on wollastonite (CaSiO3). SDTrimSP results for the default atomic model and the newly implemented oxide model recreate experimental data from [4] reasonably well compared to the commonly used SRIM. [1] Jäggi, N., et al. (2021). Icarus, 365, 114492. [2] Ziegler, J.F., et al. (2010). Nucl. Instrum. Methods Phys. Res. B, 268, 1818–1823. [3] Biber H., et al. (2020). Nucl. Instrum. Methods Phys. Res. B, 480, 10. [4] Szabo, P.S., et al. (2018). Icarus, 314, 98–105. [5] Mutzke, A., et al. (2019). SDTrimSP Version 6.00. Max-Planck-Institut für Plasmaphysik. [6] Möller, W., & Eckstein, W. (1984). Nucl. Instrum. Meth. B., 2(1–3), 814–818

The Interstellar Boundary Explorer (IBEX) has been measuring interstellar hydrogen fluxes at 1 au since 2009. In this paper, we analysed all available data obtained with the IBEX-Lo instrument at energies 11–41 eV using our numerical kinetic model of the interstellar hydrogen distribution in the heliosphere. We performed a fitting of the data to find independently the model parameters: the ratio of the solar radiation pressure to the solar gravitation (μ0), ionization rate of hydrogen atoms at 1 au (β0), parameters of the secondary interstellar atoms at 70 au from the Sun, which provide the best agreement with the data by minimization of metric χ2. We also analysed temporal variations of the ratio of the fluxes measured in a fixed direction at energy bin 1 and energy bin 2. It is found that in 2009–2011 and 2017–2016 the ratio provided by the model is smaller than in the IBEX-Lo data, while in 2012–2015, oppositely, the model ratio is larger compared to the data. This might be caused by the incorrect separation of the measured fluxes between energy channels in the data, or by some additional physical factors that are omitted in the model. Understanding this issue may be important for the preparation of future Interstellar Mapping and Acceleration Probe mission. At this stage, we relied on the sum of the fluxes measured in energy bins 1 and 2 for comparison to model predictions.

We present 3D Monte-Carlo simulation results for the surface-sputtered and sublimated H2O molecules in Ganymede's atmosphere. To calculate particle fluxes onto Ganymede's surface, we use test particle model results for electrons, thermal H+ and O+, energetic H+, O++, and S+++, with unprecedented energy resolution. In addition, besides a thermal model based on Galileo measurements, we use recently published surface water content maps and recently measured water sputter yields.Our simulations show that for the sputtered atmosphere, it is mainly the impinging O+, O++, and S++ ions that deliver H2O to the atmosphere, while electrons and protons only play a minor role in comparison. With Ganymede's surface temperature ranging from 80 K to 150 K (the latter being an upper bound), most returning H2O molecules stick to the surface. As a consequence of this, the morphology of Ganymede's magnetosphere, and the resulting patterns in the precipitation maps, are well preserved in the exosphere up to altitudes of a few thousand kilometers.In the sub-solar region, it is the sublimated H2O that dominates the atmosphere by up to four orders of magnitude. The sublimated atmosphere quickly decreases with altitude, though, and sputtering becomes the dominant release process for H2O molecules reaching beyond a few hundred kilometers altitude. The sublimated H2O atmosphere is thus quite substantial but highly limited in spatial extent.In addition to our most important modeling results concerning Ganymede's H2O atmosphere, we will also discuss their implications for spacecraft observability. Using the recently updated JUICE trajectories (CREMA 5), we will show which atmospheric populations (sublimated and/or sputtered H2O) will be encountered during the different Ganymede orbit phases (elliptical, high polar, and low polar). Finally, we will present expected measurement results for the Neutral and Ion Mass spectrometer (NIM), part of the Particle and Environment Package (PEP) onboard JUICE / ESA.

In modelling the exosphere formation of atmosphere-less planetary objects [1], the sputtering contributions is often calculated using Monte-Carlo style simulations like SRIM [2]. However, input parameters of these codes often need to be adapted to successfully describe experimental data [3].To provide such experimental data, we perform sputter measurements in which we irradiate mineral samples relevant for modelling the surfaces of Mercury or the Moon. Usually, such experiments are performed using thin sample films deposited onto a Quartz Crystal Microbalance (QCM), allowing to determine mass changes in real time and in situ [4, 5]. Advancing on this technique, we conduct measurements using a previously presented setup with a second QCM facing the irradiated samples [6]. It collects particles liberated by sputtering and probes their angular distribution. This setup allows for experiments with bulk samples, including pellets made of mineral powders [7]. These are currently being used in addition to the aforementioned thin films on primary QCMs. The goal with these samples is to detect possible differences in sputtering behaviour between the amorphous films and the bulk specimens that might be explained by crystallinity [8].Experiments with such an advanced setup require an optimisation of the measurement procedure. Due to the high sensitivity of the QCM technique, small fluctuations in the experimental conditions can lead to noticeably different catcher signals. We therefore adapted the setup geometry to ensure constant relative distances between all specimens. Additionally, sample preparation cycles were changed to minimise transient effects on the QCMs which can be caused by non-equilibrium sticking on the catcher QCM. Furthermore, data evaluation was adapted to focus on relative changes from thin film to pellet measurements, rather than absolute signals. We immediately irradiate both types of samples after each other at a fixed catcher angle. This allows us to neglect long-term changes in experimentation parameters at this chosen position. Using these procedures, we can reliably reproduce irradiation results. We are therefore capable of precisely measuring sputtering yields and angular distributions of atoms sputtered by solar wind ions for bulk samples.References [1] Wurz P., et al.: Icarus, 191, 486, 2007. [2] Ziegler, J. F., et al.: Nucl Instrum Methods Phys Res B, 268, 1818, 2010. [3] Schaible, M. J., et al.: J. Geophys. Res. Planets, 122, 1968, 2017. [4] Hayderer G., et al.: Rev. Sci. Instrum., 70, 3696, 1999. [5] Szabo P. S., et al.: Icarus, 314, 98, 2018. [6] Biber H., et al.: EPSC2021, online, EPSC2021-526, 2021. [7] Jäggi N., et al.: Icarus, 365, 114492, 2021. [8] Schlueter, K., et al.: Phys. Rev. Lett., 125.22, 225502, 2020.

The pristine very local interstellar medium (VLISM) is not available for in situ observations even with the Voyager spacecraft because the influence of the heliosphere on the VLISM plasma extends up to several hundred au from the Sun. Therefore, observations of interstellar neutral (ISN) helium, the species least modified at the heliospheric boundaries, are used to determine the pristine VLISM flow speed, direction, and temperature. For more than one solar cycle, the Interstellar Boundary Explorer (IBEX) has sampled ISN helium atoms at 1 au, significantly reducing the statistical uncertainties of the ISN helium flow parameters. Launching in 2025, the Interstellar Mapping and Acceleration Probe (IMAP) will further lower these uncertainties thanks to the utilization of a pivot platform, which provides a range of viewing orientations and reduces the parameter degeneracy seen from IBEX data. Even though interstellar helium is the least modified ISN species, recent studies show that the ISN helium flux is affected by charge exchange and elastic collisions beyond the heliopause. Charge exchange collisions outside the heliopause filter the primary ISN helium and produce a secondary population from perturbed He+ ions in the interstellar plasma. The secondary helium population, originally called the Warm Breeze, was discovered from IBEX observations. Moreover, the distribution function of the primary ISN helium population is modified by elastic collisions with slowed down and heated plasma ahead of the heliopause. Consequently, the combined primary and secondary ISN helium populations at 1 au are complex and cannot be separated. Furthermore, the modifications of the population properties are larger than the statistical uncertainty of IBEX observations. We use global heliosphere models to estimate the magnitude of the filtration and scattering caused by charge exchange and elastic collisions. Together with other sources of information about the VLISM, these estimates allow us to assess the pristine VLISM conditions outside of heliosphere influences.

Thin, collisionless atmospheres are created around otherwise atmosphere-free celestial bodies through space weathering processes. Impinging solar wind ions eject highly energetic particles into these atmospheres by sputtering. Some ejected particles escape from the atmosphere, some return to the surface or are ionized and might be caught in a surrounding magnetosphere or the solar wind plasma. This process can be observed far into space through ground based and in-situ observations.Determining the sputter yield of the various species from a realistic mineral surface is still a work in progress [1]. Modeling of sputtering with commonly used Binary Collision Approximation (BCA) models such as TRIM [2] has been shown to overestimate the sputter yields compared to experimental data [3, 4]. The number of sputter experiments performed on rock forming minerals is growing steadily, however. We apply the latest findings to obtain yields for a range of minerals from the state-of-the-art model SDTrimSP [5], which is based on TRIM. To obtain yields of surface compositions of rocky bodies we present an approximation through weighing each mineral’s sputter yield contribution. This improves upon the simplification of assuming a bulk surface composition with TRIM and the resulting overestimated sputter yields. Simulating each mineral separately with SDTrimSP and considering the current knowledge on sputter behavior is tedious and requires extensive computing power. For this reason, we develop a database of sputter yields for important rock-forming minerals allowing easy access for researchers on which we will show our progress. [1] Jäggi, N., et al. (2021). Icarus, 365, 114492. [2] Ziegler, J.F., et al. (2010). Nucl. Instrum. Methods Phys. Res. B, 268, 1818–1823. [3] Biber H., et al. (2020). Nucl. Instrum. Methods Phys. Res. B, 480, 10. [4] Szabo, P.S., et al. (2018). Icarus, 314, 98–105.[5] Mutzke, A., et al. (2019). SDTrimSP Version 6.00. Max-Planck-Institut für Plasmaphysik.

The IMAP mission by NASA is dedicated to extending the physical understanding of our heliosphere and its interaction with the interstellar medium by enhancing and refining the results obtained from IBEX. The neutral atom analysis instrument IMAP-Lo will observe and map fluxes of low-energy heliospheric neutral atoms (ENAs) and interstellar neutral (ISN) H, D, He, O and Ne with energies as low as 10 eV up to 1000 eV.The instrument testing and calibration with a neutral atom beam is foreseen in the MEFISTO test facility for ion and neutral particle instruments at the University of Bern. MEFISTO is equipped with an electron-cyclotron resonance ion source that provides ion beams at a beam energy 3keV/q up to 100 keV/q. The beam fed into the test chamber is decelerated to 10 eV/q – 3 keV/q and effectively neutralized in a removable neutralization stage via surface reflection on a highly polished single crystal tungsten surface. The relative neutral beam intensity is permanently monitored via the neutralizing surface current. The neutralization process induces a considerable reduction of particle kinetic energy and conical widening of the neutral beam.Thus, one key improvement for the calibration of a neutral atom instrument such as IMAP-Lo is to be able to measure the absolute neutral particle flux and beam energy into the instrument in the test chamber. To achieve this goal, the Absolute Beam Monitor (ABM) was developed recently.The ABM is a dedicated laboratory device for absolute neutral particle flux measurements below 3 keV and coarse kinetic energy determination. Neutrals entering the ABM aperture strike a single crystal W conversion surface at grazing angle and are reflected into a channeltron to generate a stop pulse. The simultaneous monitoring of secondary electrons released at the W surface as start signal, the stop signal and the coincidence event rate allows inferring the rate of neutral atoms into the ABM aperture. The average neutral beam energy is obtained from the start-stop time-of-flight spectrum. The ABM is the first and so far the only device to measure the absolute neutral atoms flux in this low energy range below a few 100 eV. It serves as a primary standard for gauging the MEFISTO neutral beam source.We report on recent calibration results of neutral H, He, O, Ne beams in the 10 eV – 1 keV energy range with the ABM in MEFISTO.

Energetic neutral atoms (ENAs) are produced by the neutralization of energetic ions formed by shock-accelerated gradual solar energetic particle events (SEP). These high-energy ENAs (HENAs) can reach the Earth earlier than the associated SEPs and provide information about the SEPs at the lower corona. The HENA properties observed at Earth depend on the properties of the coronal mass ejection (CME)-driven shocks that accelerate the SEPs. With a model of HENA production in a shock-accelerated SEP event, we semi-quantitatively investigate the energy-time spectrum of HENAs depending on the width, propagation speed, and direction of the shock, as well as the density and ion abundances of the lower corona. Compared to the baseline model parameters, the cases with a wider shock width angle or a higher coronal density would increase the HENA flux observed at the Earth, while the case with an Earth-propagating shock shows a softened HENA spectrum. The comparison of expected HENA fluxes in different cases with a flight-proven ENA instrument suggests that solar HENAs can feasibly be monitored with current technologies, which could provide a lead time of 2-3 hours for SEPs at a few MeV. We propose that monitoring of solar HENAs could provide a new method to forecast shock-driven SEP events that could have significant space weather impacts on the near-Earth environment.

A simulation tool which utilizes parallel processing is developed to describe molecular kinetics in 2D, single- and multi-component atmospheres on Callisto. This expands on our previous study on the role of collisions in 1D atmospheres on Callisto composed of radiolytic products (Carberry Mogan et al., 2020) by implementing a temperature gradient from noon to midnight across Callisto’s surface and introducing sublimated water vapor. We compare single-species, ballistic and collisional O 2 , H 2 and H 2 O atmospheres, as well as an O 2 +H 2 O atmosphere to 3-species atmospheres which contain H 2 in varying amounts. Because the H 2 O vapor pressure is extremely sensitive to the surface temperatures, the density drops several orders of magnitude with increasing distance from the subsolar point, and the flow transitions from collisional to ballistic accordingly. In an O 2 +H 2 O atmosphere the local temperatures are determined by H 2 O near the subsolar point and transition with increasing distance from the subsolar point to being determined by O 2 . When radiolytically produced H 2 is not negligible in O 2 +H 2 O+H 2 atmospheres, this much lighter molecule, with a scale height roughly an order of magnitude larger than that for the heavier species, can cool the local temperatures via collisions. In addition, if the H 2 component is dense enough, particles originating on the day-side and precipitating into the night-side atmosphere deposit energy via collisions, which in turn heats the local atmosphere relative to the surface temperature. Moreover, the difference between H 2 atmospheric escape rates in single-species and multi-species atmospheres is small: the H 2 only has to diffuse through a few hundred km of the heavier gases before it is the lone species in the atmosphere out to the Hill sphere. Finally, we discuss the potential implications of this study on the presence of H 2 in Callisto’s atmosphere and how the simulated densities correlate with expected detection thresholds at flyby altitudes of the proposed JUpiter ICy moons Explorer (JUICE) spacecraft.

The parameter space for the very uncertain composition of sublimated H2O and its photochemical products H and H2 in Callisto's atmosphere is examined using the Direct Simulaton Monte Carlo (DSMC) method. We focus on two significantly different versions of H2O production in which: (1) the ice and dark, non-ice/ice-poor material are intimately mixed and H2O sublimates at Callisto's warm day-side temperatures (e.g., as in most atmospheric modeling efforts at Callisto to date [1-4]); and (2) the ice and dark, non-ice/ice-poor material are segregated (e.g., consistent with interpretations of images of Callisto's surface taken by Voyager [5, 6] and Galileo [7]) and H2O sublimates at "ice" temperatures [8]. Our 2D molecular kinetic models track the motion H2O, whose sublimation yield varies several orders of magnitude depending on the description of Callisto's surface, its photochemical products H and H2, and a relatively dense O2 component. Whereas H is assumed to react in the regolith on return to the surface, H2 is assumed to thermalize and re-enter the atmosphere. We compare the simulated LOS column densities of H to the detected H corona at Callisto [9], which was suggested to be produced primarily by photodissociation of sublimated H2O. Our goal is to use the corona observations to help constrain the source rate for H2O from Callisto’s complex surface. References [1] Liang et al., 2005. Atmosphere of Callisto. Journal of Geophysical Research: Planets. [2] Vorburger et al., 2015. Monte-Carlo simulation of Callisto’s exosphere. Icarus. [3] Hartkorn et al., 2017. Structure and density of Callisto’s atmosphere from a fluid-kinetic model of its ionosphere: Comparison with Hubble Space Telescope and Galileo observations. Icarus. [4] Carberry Mogan et al., 2021 (under review). A tenuous, collisional atmosphere on Callisto. Icarus. [5] Spencer and Maloney, 1984. Mobility of water ice on Callisto: Evidence and implications. Geophysical Research Letters. [6] Spencer, 1987. Thermal segregation of water ice on the Galilean satellites. Icarus. [7] Moore et al., 1999. Mass movement and landform degradation on the icy Galilean satellites: Results of the Galileo nominal mission. Icarus. [8] Grundy et al., 1999. Near-infrared spectra of icy outer solar system surfaces: Remote determination of H2O ice temperatures. Icarus. [9] Roth et al., 2017. Detection of a hydrogen corona at Callisto. Journal of Geophysical Research: Planets.

The JUpiter ICy moons Explorer (JUICE) of the European Space Agency will investigate Jupiter and its icy moons Europa, Ganymede, and Callisto, with the aim to better understand the origin and evolution of our Solar System and the emergence of habitable worlds around gas giants. The Particle Environment Package (PEP) on board JUICE is designed to measure neutrals, ions, electrons, and energetic particles over an energy range from eV to MeV. In the vicinity of Callisto, PEP will characterize the Jovian plasma environment and the outer parts of Callisto’s atmosphere and ionosphere. Roughly twenty Callisto flybys with closest approaches between 200 km and 5000 km altitude are planned over the course of the JUICE mission. This study aims at optimizing the scientific insight gained from the foreseen flybys by combining the input from the PEP science team and operation planning with recent model efforts for Callisto’s atmosphere, the plasma environment and the production of Energetic Neutral Atoms. The results of this study will inform both science operation planning of PEP and JUICE and they will guide future model development for Callisto’s atmosphere, ionosphere, and their interaction with the plasma environment.

Atmosphere-free celestial bodies are constantly irradiated by solar wind or magnetospheric ions. In the case of Mercury, the intrinsic magnetic field, although weak, leads to localized plasma precipitation around the magnetospheric cusps and nightside precipitation below the magnetotail [1, 2, 3]. The material ejected by the impacting ions (sputtering) thereby contributes to the exosphere and magnetosphere surrounding Mercury [4, 5, 6]. Magnetospheric ions originate from ionization of exospheric atoms or ions directly sputtered from the surface. Those can become part of the magnetospheric plasma, and have trajectories that lead them back to Mercury’s surface [7, 8]. We explored different scenarios of the sputtering of Mercury’s surface with a strong focus on dynamic surface alteration and sputtering. This includes time varying inputs from varying solar wind conditions as well as contributions of secondary ions originating from Mercury’s exosphere and magnetosphere. We rely on the dynamic sputter model SDTrimSP [9] and compare the simulation results with more simplistic TRIM [10] simulations as well as recent laboratory results of solar wind ion sputtering on Mercury analogues [11, 12, 13]. [1] Winslow, R.M., et al. (2017). J. Geophys.Res.-Space, 122(5), 4960–4975. [2] Winslow, R.M., et al. (2014). Geophys. Res. Lett., 41(13), 4463–4470. [3] Schmidt, C.A. (2013). J. Geophys.Res.-Space, 118(7), 4564–4571. [4] Killen, R.M., & Ip, W. H. (1999). Rev. Geophys., 37(3), 361–406. [5] Raines, J.M., et al. (2016). Plasma Sources of Solar System Magnetospheres (pp. 91–144). Springer. [6] Wurz, P., et al., (2019). J. Geophys. Res., 124, 2603–2612. [7] Yagi, M., et al. (2017). J. Geophys.Res.-Space, 122(11), 10,990-11,002. [8] Delcourt, D.C., et al. (2003). Ann. Geophys., 21(8), 1723–1736. [9] Mutzke, A., et al. (2019). SDTrimSP Version 6.00. Max-Planck-Institut für Plasmaphysik. [10] Ziegler, J.F., et al. (2010). Nucl. Instrum. Methods Phys. Res. B, 268, 1818–1823. [11] Jäggi, N., et al. (2021). Icarus, 365, 114492. [12] Biber H., et al. (2020). Nucl. Instrum. Methods Phys. Res. B, 480, 10. [13] Szabo, P.S., et al. (2018). Icarus, 314, 98–105.

During its evolution, the Sun and its protective magnetic bubble – the heliosphere - has completed nearly twenty revolutions around the Galactic Core. During this “Solar Journey” it has plowed through widely different interstellar environments that have all shaped the system we live in today. The orders-of-magnitude differences in interstellar properties have had dramatic consequences for the penetration of interstellar material and have affected elemental and isotopic abundances, atmospheric evolution and perhaps even conditions for habitability. As far as we know, only some 60, 000 years ago, the Sun entered what we call the Local Interstellar Cloud (LIC), and in less than 1,900 years the Sun will be entering a very different interstellar environment that will continue to shape its evolution and fate.The Interstellar Probe is a pragmatic mission with a possible launch already in the next decade that would explore the heliospheric boundary and how it interacts with the Very Local Interstellar Medium (VLISM) to understand the current state along this Solar Journey and, ultimately understand where our home came from, and where we are going. During its 50-year nominal design life, it would go far beyond where the Voyager missions have gone, out to about 400 astronomical units (au) and likely survive out to 1000 au. Therefore, the Interstellar Probe mission would represent humanity’s first explicit step in to the galaxy and become NASA's boldest step in space exploration.When the Voyager missions traversed the heliospheric boundary with their very limited payload it became clear that we are faced with a whole new regime of space physics that is not only decisive for our own heliosphere, but also for understanding the physics of other astrospheres as well. Today we still do not understand the force that is upholding the magnetic shell (the heliosheath) around our heliosphere, or the mechanisms that shield the solar system from galactic cosmic rays, and many other mysteries. Once beyond where the furthest Voyager spacecraft will cease operations (likely at ~170 au), Interstellar Probe would step in to the unknown, traverse the hydrogen wall and the complex magnetic topology at the very edge of the Sun’s sphere of influence, and then directly sample for the first time the interstellar material that has made all of us. There, measurements of the unperturbed gas, plasma, and fields would allow accurate determination of the current state of the LIC and how it affects the global heliosphere. Measurements of unshielded interstellar dust and galactic cosmic rays would provide unprecedented information on stellar and galactic evolution. The physical processes that occur as the solar wind and magnetic field interact with VLISM would also provide the only directly measurable prototypes for understanding the astrospheres surrounding other stars that control the atmospheres and habitability of their exoplanets. All this newly acquired knowledge would then enable an understanding of the current state of the heliosphere and the VLISM, and how they interact, which ultimately can be used to extrapolate the understanding of our system back to the past and into the future.At the same time, the outward trajectory is a natural opportunity for exploring one of the ~4,000 Kuiper Belt Objects or ~130 dwarf planets similar to and beyond Pluto and determine the large-scale structure of the circum-solar dust disk to provide the ground truth for planetary system formation in general. Once beyond the obscuring dust, the infrared sky would open a window to early galaxy formation.An Interstellar Probe has been discussed and studied since 1960, but the stumbling block has always been propulsion. Now this hurdle has been overcome by the availability of new and larger launch vehicles. An international team of scientists and experts are now in the final year of a NASA-funded study led by The Johns Hopkins University Applied Physics Laboratory (APL) to develop pragmatic example mission concepts for Interstellar Probe with a nominal design lifetime of 50 years. Together with the Space Launch System (SLS) Program Office at NASA’s Marshall Space Flight Center, the team has analyzed dozens of launch configurations and demonstrated that asymptotic speeds in excess of 7.5 au per year can be achieved using existing or near-term propulsion stages with a powered or passive Jupiter Gravity Assist (JGA). These speeds are more than twice that of the fastest escaping man-made spacecraft to date, which is Voyager 1 currently at 3.59 au/year. Launching near the nose direction of the heliosphere, Interstellar Probe would therefore reach the Termination Shock (TS) in less than 12 years and cross the Heliopause into the VLISM after about 16 years from launch.In this presentation we provide an overview and update of the study, the science mission concept, the compelling discoveries that await, and the associated example science payload, measurements and operations ensuring a historic data return that would push the boundaries of space exploration by going where no one has gone before.

1. IntroductionIons from the solar wind impinging on airless planetary bodies eject particles from the very surface. Those sputtering processes can also be caused by ions originating from planetary bodies in the direct vicinity. This type of process occurs on the martian moon Phobos, where molecules from the upper atmosphere of Mars are ionized, accelerated and subsequently impact the surface of Phobos [1, 2]. The particles ejected due to ion sputtering typically have an energy of a few eV [3]. For lighter elements, this leads to a significant fraction of them leaving the gravitational field of bodies like Mercury, where an escape velocity of 4.25 km/s corresponds to about 1.5 eV for oxygen [4]. Those particles that are emitted at lower energies are still coupled to the planet‘s gravitational field and contribute to the formation of a so-called exosphere, i.e. a zone with elevated density around airless bodies. Modeling of the exosphere requires accurate sputtering data as input. A common way of obtaining these data is through the simulation package SRIM, which can provide an estimate for sputtering yields, but is known for its deviations from experimentally obtained values. Improvements can be made by using the SDTrimSP code, but here input parameters have to be set manually to achieve satisfactory agreement with measurements [5]. In both models, amorphous samples are assumed for the simulation and no effects of crystallinity are taken into account. However, these effects can vary from drastic suppression of sputtering due to channeling in single crystals [6] to an increase in sputtering due to linear collision sequences in polycrystalline materials [7]. Experimental investigations of mineral sputtering also mostly use amorphous films [8, 9]. This is due to the use of Quartz Crystal Microbalances (QCM) in sputtering experiments, which allow determining mass changes in the sub-monolayer range in real time and in situ [10]. For experiments with more realistic crystalline minerals however, different approaches have to be used. 2. A novel setupThe new setup for sputtering investigations for minerals at TU Wien is based on catching the material sputtered from samples rather than measuring mass depletion of an irradiated sample [11, 12]. This is accomplished by the use of a QCM in a catching configuration (Figure 1). With this approach, a much wider range of samples can be investigated. Due to the use of two independent rotary manipulators, the angular dependence of the sputteringprocesses (variation of α in Figure 1) as well as the angular distribution of sputtered particles (variation of αC ) can be analyzed. Figure 1: Geometry of the measurements using a QCM to catch sputtered material. Both angles α and αC can be varied independently. Figure taken from [12]. Surface roughness has to be taken into account in sputtering experiments. It has a significant influence on ion sputtering and it is therefore necessary to characterize the surface morphology of irradiated samples in order to derive the correct conclusions [13] . For this purpose, an Atomic Force Microscope is used to precisely map the topography of the irradiated samples surfaces at the nanometer scale. 3. No effects of crystallinity observedThe combination of both a thin wollastonite CaSiO3 based film on a QCM and a pressed wollastonite pellet as samples allows for direct comparison of the signals measured at the catching QCM [14]. Only minor deviations from flat surfaces were expected due to roughness effects. The samples were irradiated with 2 keV Ar+ ions under an angle of incidence of α = 60°. The angular distribution of sputtered particles was analyzed for both samples by varying the catcher angle αC. The signal of the catcher QCM normalized to the ion current is shown in Figure 2. Within measurement uncertainties, no difference in signal per impinging ion was found. This indicates that crystallinity does not have a significant influence on the sputtering of mineral samples, but further measurements are needed for more conclusive statements about the relevance of the materials phase for sputtering effects on celestial bodies like Mercury.Figure 2: Signal of the catcher QCM per incident ion measured at different catcher QCM angles αC for irradiations with 2 keV Ar+ on wollastonite CaSiO3 at α = 60°. References[1] Nenon Q., et al.: J. Geophys. Res. Planets, 124, 3385, 2019.[2] Szabo P.S., et al.: J. Geophys. Res. Planets, 125, e2020JE006583, 2020.[3] Betz G., et al.: Int. J. Mass Spectrom., 140, 1, 1994.[4] Williams, D.R.: Mercury Fact Sheet, 25 Nov. 2020, https://nssdc.gsfc.nasa.gov/planetary/factsheet/mercuryfact.html, (Accessed 17. May 2020).[5] Szabo, P.S., et al.: Astrophys. J., 891, 100, 2020.[6] Onderdelingen D.: Appl. Phys. Lett., 8, 189, 1966.[7] Schlueter K., et al.: Phys. Rev. Lett., 125, 225502, 2020.[8] Hijazi H., et al.: J. Geophys. Res. Planets, 122, 1597, 2017.[9] Biber H., et al.: Nucl. Instrum. Methods Phys. Res. B, 480, 10, 2020.[10] Hayderer G., et al.: Rev. Sci. Instrum., 70, 3696, 1999.[11] Berger B. M., et al.: Nucl. Instrum. Methods Phys. Res. B, 406, 533, 2017.[12] Biber H., et al.: EPSC Abstracts, 14, EPSC2020-264, 2020.[13] Küstner M., et al.: Nucl. Instrum. Methods Phys. Res. B, 145, 320, 1998.[14] Jäggi N., et al.: Icarus, 365, 114492, 2021.

The surface of bodies without a thick atmosphere in outer space is exposed to the harsh space environment [1]. Space weathering alters its properties and leads to the formation of a tenuous exosphere. This elevated density of particles is coupled to the surface and therefore carries information about the latter. The BepiColombo mission aims to probe the composition of Mercury’s exosphere for the purpose of extracting this information [2]. However, this task requires precise models of exosphere formation [3]. Sputtering by solar wind ions is expected to be one of the main drivers for exosphere formation and models are therefore sensitive to sputtering inputs. So far, mainly simulation data are used, as experimental sputtering data for relevant materials are rare. Furthermore, available measurements have been typically performed with amorphous thin films due to use of the Quartz Crystal Microbalance (QCM) technique for sputtering measurements [4, 5]. Such a QCM is very sensitive to mass changes with resolutions in the sub mono-layer regime and is therefore an ideal tool for quantitative measurements of sputtering yields [6].We introduce a new method for determining sputtering yields of more realistic samples, which allows to overcome the limitations of thin films while making use of the high sensitivity of QCMs. For this purpose, pellets pressed from minerals that are relevant for Mercury are used. The primary sample holder is placed on a xyzφ -manipulator, which enables switching between different samples and varying the irradiation angle α. A secondary quartz (C-QCM) is placed on an independently rotatable manipulator. This setup allows probing the angular distribution of sputtered particles by determining the mass change ∆m ion−1 in dependence on the angle αC between the sample and the C-QCM, which can lead to further improvement of exosphere models. Furthermore, mass changes of the irradiated sample due to ion implantation [7], can be untangled as only deposition of ejected particles contributes to the C-QCM signal. The use of pressed pellets enables a variation in sample parameters not accessible with thin films like crystal structure, surface roughness and porosity. Nonetheless, a QCM coated with the same material is installed on the primary sample holder in addition to the pellet for calibration.First results with the Ca-pyroxenoid wollastonite (CaSiO3) and 2 keV Ar+ ions are very promising. They indicate no difference in sputtering of the amorphous thin film and the pressed wollastonite pellet for Ar+ irradiations. In a next step, solar wind ions will be used, which will improve the understanding of sputtering of realistic samples by solar wind ions. References[1] Hapke B.: J. Geophys. Res. Planet., 106, 10039, 2001.[2] Milillo A., et al.: Planet. Space Sci., 58, 40, 2010.[3] Wurz P., et al.: Planet. Space Sci., 58, 1599, 2010.[4] Szabo P. S., et al.: Astrophys. J., 891, 100, 2020.[5] Hijazi H., et al.: J. Geophys. Res. Planets, 122, 1597, 2017.[6] Hayderer G., et al.: Rev. Sci. Instrum., 70, 3696, 1999.[7] Biber H., et al.: Nucl. Instrum. Methods Phys. Res. B, 480, 10, 2020.

The Interstellar Probe is a space mission to discover physical interactions shaping globally the boundary of our Sun`s heliosphere and its dynamics and for the first time directly sample the properties of the local interstellar medium (LISM). Interstellar Probe will go through the boundary of the heliosphere to the LISM enabling for the first time to explore the boundary with a dedicated instrumentation, to take the image of the global heliosphere by looking back and explore in-situ the unknown LISM. The pragmatic concept study of such mission with a lifetime 50 years that can be implemented by 2030 was funded by NASA and has been led by the Johns Hopkins University Applied Physics Laboratory (APL). The study brought together a diverse community of more than 400 scientists and engineers spanning a wide range of science disciplines across the world.Compelling science questions for the Interstellar Probe mission have been with us for many decades. Recent discoveries from a number of space missions exploring the heliosphere raised new questions strengthening the science case. The very shape of the heliosphere, a manifestation of complex global interactions between the solar wind and the LISM, remains the biggest mystery. Interpretations of imaging the heliosphere in energetic neutral atoms (ENAs) in different energy ranges on IBEX and Cassini/INCA from inside show contradictory pictures. Global physics-based models also do not agree on the global shape. Interstellar Probe on outbound trajectory will image the heliosphere from outside for the first time and will provide a unique determination of the global shape.The LISM is a completely new area for exploration and discovery. We have a crude understanding of the LISM inferred from in-situ measurements inside the heliosphere of interstellar helium, pick-up-ions, ENAs, remote observations of solar backscattered Lyman-alpha emission and absorption line spectroscopy in the lines of sight of stars. We have no in-situ measurements of most LISM properties, e.g. ionization, plasma and neutral gas, magnetic field, composition, dust, and scales of possible inhomogeneities. Voyagers with limited capabilities have explored 30 AU beyond the heliosphere which appeared to be a region of significant heliospheric influence. The LISM properties are among the key unknowns to understand the Sun`s galactic neighborhood and how it shapes our heliosphere. Interstellar Probe will be the first NASA mission to discover the very nature of the LISM and shed light on whether the Sun enters a new region in the LISM in the near future.In this presentation we give an overview of heliophysics science for the Interstellar Probe mission focusing on the critical science questions of the three objectives for the mission. We will discuss in more details a need for direct measurements in the LISM uniquely enabled by the Interstellar Probe.

The search for life is one of the key topics in modern space science. The JUICE mission of the European Space Agency ESA will investigate Jupiter and its icy moons Ganymede, Callisto and Europa, with Europa being an example of a potentially habitable world around a giant gas planet. The Particle and Environment Package, PEP, on board of the JUICE spacecraft will investigate Jupiter’s icy moons and their environment. The Neutral gas and Ion Mass spectrometer NIM will investigate the icy moon’s exospheres to investigate their formation and the interaction processes of the exospheres with the moons’ surface and Jupiter’s strong magnetic field. It will enhance our understanding of the processes involved in the interactions of ion bombardment on the icy moons' surfaces. From these measurements, we will derive the moons’ surface composition and their formation processes.NIM is a time-of-flight mass spectrometer with two particle entrances: an open-source entrance to measure neutral particles and ions directly and a close source entrance where neutral particles get thermalized before entering the sensor’s ionization region. This allows detecting of particles with high speeds. NIM has a specially designed ion storage source and an ion-mirror to double the flight distance of the produced ions by keeping the sensor at a minimal size.In this contribution, we show calibration results of the NIM flight spare instrument on one hand operated with laboratory and on the other operated with flight electronics. We demonstrate the performance of NIMs ion-source, verify the performance of the closed-source antechamber. NIM has a demonstrated mass resolution of m/Δm 800.

Recent modelling efforts based on MAVEN measurements suggest that the Martian Moon Phobos is affected by a unique space weathering scenario [1]. On rocky bodies in the solar system, mostly solar wind ions cause ion-induced space weathering of their surfaces. Space weathering is an important driver for the alteration of planetary surfaces [2], as well as for the creation of exospheres on, for example, the Moon or Mercury [3, 4]. As a consequence, most analog experiments aim to investigate effects by the impact of solar wind ions [5, 6].Phobos is not only exposed to the solar wind, but also significantly sputtered by planetary oxygen ions originating from the Martian atmosphere due to its proximity to Mars [7]. O ions at energies of several 100s to several 1000s eV are responsible for the dominant erosion process on the surface of Phobos in the Martian magnetotail [1]. However, there still remain uncertainties as the sputtering by planetary O ions has not yet been investigated experimentally.Here we present experiments on the sputtering of Phobos analog materials by O+ and O2+ ions at different energies [8]. As analog material, thin films of augite (Ca,Mg,Fe)2Si2O6 on a quartz crystal microbalance (QCM) are used. The QCM allows in-situ real-time sputtering experiments by measuring the sample’s mass change [9]. Experimental sputtering yields are compared to simulations with the SRIM package and SDTrimSP [10, 11]. The latter has shown better accuracy for reproducing sputtering yields [6, 12], which is also found in the presented studies [8].Oxygen ion irradiations of Phobos analog materials show fluence-dependent mass changes, indicating that both sputtering and O ion implantation in the near-surface region occur at the same time. The measurements can be consistently reproduced by dynamic SDTrimSP simulations that include O implantation up to local concentrations of 67%. The new experimental findings show that sputtering by O ions is about 50% lower than previously assumed. However, our measurements still support the importance of sputtering by planetary ions in the Martian tail, where it will dominate over solar wind sputtering by up to a factor of 10 [8]. References [1] Q. Nenon, et al., J. Geophys. Res.: Planets 124 (2019), 3385[2] B. Hapke, J. Geophys. Res.: Planets 106 (2001), 10039[3] P. Wurz, et al., Icarus 191 (2007), 486[4] R.M. Killen, et al., Space Sci. Rev. 132 (2007), 509[5] H. Hijazi, et al., J. Geophys. Res.: Planets 122 (2017), 1597[6] P.S. Szabo, et al., Astrophys. J. 891 (2020), 100[7] A.R. Poppe, S.M. Curry, Geophys. Res. Lett. 41 (2014), 6335[8] P.S. Szabo, et al., J. Geophys. Res.: Planets 125 (2020), e2020JE006583[9] G. Hayderer, et al., Rev Sci. Instrum., 70 (1999), 3696[10] J. Ziegler, et al., NIMB, 268 (2010), 1818[11] A. Mutzke, IPP-Report 2019-02 (2019)[12] M. Schaible, et al., J. Geophys. Res.: Planets 122 (2017), 1968

The large iron core of Mercury and the low iron contents on the surface inferred from MESSENGER data suggest the presence of a magma ocean after accretion. We modeled the lifetime of an early Hermean magma ocean as well as the structure and loss rates of an atmosphere that is sourced by degassing. We use a large range of initial conditions including several bulk compositions associated with varying degrees of differentiation, the inclusion of carbon and hydrogen degassing volatiles such as CO2 and H2O, as well as considering a larger proto-Mercury size. After obtaining the magma ocean lifetime and volatile vapor pressures, the result is passed on to further models to obtain metal oxide vapor pressures, a complete atmospheric photochemical speciation and ultimately the mass loss rate of the atmosphere.We show that magma ocean cooling times are sensitive to the size of the planet and the efficiency of radiative heat transfer in the atmosphere. A volatile-free proto-Mercury radiating as a blackbody with its present-day size would cool down within 400 years from an assumed initial surface temperature of 2500 K to an early crust formation threshold of 1500 K. In contrast it takes 9000 years for a volatile rich proto-Mercury with a greenhouse atmosphere and a mantle size representing Mercury before the occurrence of a mantle stripping event. Volatile-rich cases reach massive atmosphere pressures, whereas volatile-free cases are dominated by Si, Na, K, Mg, and Fe species degassed from the magma ocean and end up at a maximum pressure of 0.1 bar at 2500 K. There is however only a small difference in the atmospheric extent, as the absence of volatile species in the thin metal oxide atmosphere causes it to become extended to a degree, where an upper atmosphere height comparable to the volatile cases is reached. In terms of mass loss we found that upper atmospheric loss due to photoionization is highly efficient in the environment of a young Sun, ionizing 100% of the particles reaching Mercury’s exosphere. This leads to loss rates of up to 106 kg/s, which are however diffusion limited by the supply from the homopause, reducing them by 2-3 orders of magnitude. In regards to Na and K loss, we found that a thin, volatile-free atmosphere is most efficient with its extended structure allowing for large loss rates as well as the high Na and K mixing ratio.

The energetic neutral atom detection instrument IMAP-Lo is part of the scientific payload of the upcoming Interstellar Mapping and Acceleration Probe (IMAP) mission by NASA and is designed to analyse interstellar neutral and heliospheric Energetic Neutral Atom fluxes and their composition for energies from 1000 eV down to 10 eV. IMAP is dedicated to extend our knowledge of the local interstellar medium (LISM) and its interaction with the solar magnetic field and the heliosphere. Most importantly, H, He, O and Ne ENAs will be analysed.Calibration and testing of IMAP-Lo is planned in MEFISTO, a unique laboratory test facility for ion and neutral particle instruments at the University of Bern, which can provide the required neutral atom beams. In MEFISTO we have a microwave-induced plasma ion source for beam energies up to 100 keV/q. The ion beam can be converted to a neutral beam in the energy range 10 eV – 3 keV with a removable ion beam neutralizer with decelerating the ion beam first and subsequent neutralisation via surface reflection. It comes with an estimated beam energy reduction of 15 % and energy-dependent transmission. The neutral beam flux into the test chamber therefore depends on the ion beam energy, intensity and species. To improve the calibration process for ENA space instruments such as IMAP-Lo, it is important to measure the neutral beam flux and energy in the test facility.The Absolute Beam Monitor (ABM) is a novel laboratory device developed for absolute neutral particle flux measurements and energy determination of neutral atom beams. The ABM takes advantage of secondary electron emission during surface scattering of incident neutral atoms off a highly polished tungsten plate. The effective rate of neutrals is inferred from detecting secondary electrons and reflected atoms in two electron multipliers as well as its coincidence signal rate. Time difference of the two signals yields the neutrals energy. To date, the ABM is the only device to measure absolute fluxes of neutral atoms in this energy range.Measurements of the neutral beam source in MEFISTO have been performed for several species using the ABM to determine the relation between the effective neutral atom flux and the primary ion beam current at the charge conversion surface, as well as the neutral beam energy, for ion energies from 1000 eV down to 10 eV.

In instruments for low energetic neutral atom imaging of space plasmas, a charge state conversion surface (CS) is used to convert neutral atoms into ions for detection. We investigated a cadmium telluride (CdTe) coated sample as a novel material candidate regarding its suitability to be used as a CS. We measured the efficiency of converting H and O atoms into negative ions by surface scattering, as well as their angular scattering distribution, for energies from 195 eV to 1 keV at 8 ° incidence angle. Also, the energy distribution of scattered particles was recorded for incident O 2 + ions, which confirms that molecules are mainly scattered as single atoms. The mean energy loss per atom was about 45%. The negative ion yield from scattering off CdTe was up to 13% for O and about 2% for H, which is comparable to other CS coatings in use. CdTe shows a nearly circular angular scattering cone of width comparable to established CS materials. We conclude that CdTe is a viable CS coating material for ENA instruments in space applications.

The JUpiter ICy moons Explorer (JUICE) of the European Space Agency (ESA) will investigate Jupiter and its icy moons Europa, Ganymede and Callisto, with the aim to better understand the origin and evolution of our Solar System and the emergence of life. The Neutral gas and Ion Mass spectrometer (NIM) is one of six instruments of the Particle Environment Package (PEP) on board the JUICE spacecraft. PEP will measure neutral atoms and molecules, the ion population, and the electron population over an energy range covering from meV to MeV. The NIM instrument is designed to measure the chemical and isotope composition of the exospheres of three of Jupiter’s satellites, the icy moons, both, during several flybys and during its final destination in Ganymede orbit. From measurements of the exosphere, we will derive the chemical composition of the surface, which will allow us a better understanding of the icy moons formation processes, interactionprocesses with the magnetospheric plasma and energetic particles of Jupiter’s magnetospheric system. The NIM instrument is a compact time-of-flight mass spectrometer allowing measurements of thermal neutral molecules and ionospheric ions. To minimize the background radiation on the detector and protect electronics against the harsh radiation environment around Jupiter, elaborated radiation shielding was designed. NIM consists of two major subunits, namely, the ion-optical system and the electronics. This study presents details on the technical design and the results obtained from the calibration campaigns of different subsystems of the flight instrument including a mass range of m/z 1 to 650, a mass resolution m/Δm of at least 750 (FWHM), and an instantaneous dynamic range of almost 6 decades. These results are discussed in detail with respect to the scientific requirements. This performance in combination with its radiation tolerance allows for both a detailed analysis of the chemical composition of Jupiter’s icy moons’ exospheres and ionospheres, and to explore environments, where formation of life might be possible.

Energetic neutral atom (ENA) models typically require post-processing routines to convert the distributions of plasma and H atoms into ENA maps. Here we investigate how two different kinetic-MHD models of the heliosphere (the BU and Moscow models) manifest in modeled ENA maps using the same prescription and how they compare with Interstellar Boundary Explorer (IBEX) observations. Both MHD models treat the solar wind as a single-ion plasma for protons, which include thermal solar wind ions, pick-up ions (PUIs), and electrons. Our ENA prescription partitions the plasma into three distinct ion populations (thermal solar wind, PUIs transmitted and ones energized at the termination shock) and models the populations with Maxwellian distributions. Both kinetic-MHD heliospheric models produce a heliotail with heliosheath plasma organized by the solar magnetic field into two distinct north and south columns that become lobes of high mass flux flowing down the heliotail, though in the BU model the ISM flows between the two lobes at distances in the heliotail larger than 300 AU. While our prescription produces similar ENA maps for the two different plasma and H atom solutions at the IBEX-Hi energy range (0.5 - 6 keV), the modeled ENA maps require a scaling factor of ~2 to be in agreement with the data. This problem is present in other ENA models with the Maxwellian approximation of multiple ion species and indicates that a higher neutral density or some acceleration of PUIs in the heliosheath is required., Comment: 29 pages, 3 tables, 9 figures, accepted to ApJ

MESSENGER observations suggest a magma ocean formed on proto-Mercury, during which evaporation of metals and outgassing of C- and H-bearing volatiles produced an early atmosphere. Atmospheric escape subsequently occurred by plasma heating, photoevaporation, Jeans escape, and photoionization. To quantify atmospheric loss, we combine constraints on the lifetime of surficial melt, melt composition, and atmospheric composition. Consideration of two initial Mercury sizes and four magma ocean compositions determine the atmospheric speciation at a given surface temperature. A coupled interior-atmosphere model determines the cooling rate and therefore the lifetime of surficial melt. Combining the melt lifetime and escape flux calculations provide estimates for the total mass loss from early Mercury. Loss rates by Jeans escape are negligible. Plasma heating and photoionization are limited by homopause diffusion rates of $\sim10^{6}$ kg/s. Loss by photoevaporation depends on the timing of Mercury formation and assumed heating efficiency and ranges from $\sim10^{6.6}$ to $\sim10^{9.6}$ kg/s. The material for photoevaporation is sourced from below the homopause and is therefore energy-limited rather than diffusion-limited. The timescale for efficient interior-atmosphere chemical exchange is less than ten thousand years. Therefore, escape processes only account for an equivalent loss of less than 2.3 km of crust ($0.3\%$ of Mercury's mass). Accordingly, $\leq0.02\%$ of the total mass of H$_2$O and Na is lost. Therefore, cumulative loss cannot significantly modify Mercury's bulk mantle composition during the magma ocean stage. Mercury's high core:mantle ratio and volatile-rich surface may instead reflect chemical variations in its building blocks resulting from its solar-proximal accretion environment., 25 pages, 8 figures, accepted to be published in The Planetary Science Journal

Introduction: Telescopic and spacecraft observations of the surfaces of Jupiter’s icy moons have provided information on their composition, mostly from the spectral analysis of the reflected light [1-4]. The surfaces of these bodies are made of crystalline and amorphous water ice and several highly hydrated salty phases [1 – 9]. As several potential chemical composition are relevant for the surfaces of these moons, as much as for other bodies covered with hydrated salty phases, the laboratory work ongoing at the University of Bern intends to enlighten how different salts mixed with water ice in different ways affect the reflectance. We prepared several samples by mixing MgSO4, NaCl, MgCl2 and Na2SO4 with ices to better constrain how these components, thought to be present at global and/or local scale, can form hydrated phases depending on the preparation method, which roughly simulate processes for the production of renewed / pristine material at the surface of icy moons. The effects of the strong irradiation at the surface of Jupiter’s moons are also investigated. Flash-frozen salty ices: Granular ices have been produced through a flash-freezing process by nebulizing droplets into liquid nitrogen [10] with the SPIPA setup from the University of Bern. This preparation process tends to simulate a production of particles through an active plume or geyser at, or close to, the surface. The water ice itself is not able to incorporate salt in its crystal lattice at ambient pressure, contrary to high pressure [11, 12]. Given the temperature of liquid nitrogen, particles solidify forming amorphous or glassy phases of salt and water. This process is described in other fields of science [13] and demonstrates to which extent a flash-freezing procedure generates highly complex particles, made of different phases, both amorphous and crystalline. Slabs of salty ices: Starting from similar composition but simulating a slow freezing process, slabs of salty ices have been produced with different concentrations of salts, from low to saturated proportions (wt% of salt is varying in function of the salt). We identify the signature of different hydrates, regarding different salts, expected to form through slow crystallisation following their phase diagrams and thermodynamic equilibrium [14]. The ice itself has the time to expels salt from its crystal. This procedure could be more relevant for ice produced either inside “hydrological” analogues systems inside ice shells, or at the interface of the ice shell and the global salty ocean. By letting slabs samples sublimate slowly in vacuum, absorptions bands related to the hydrated phases appeared. Figure 1: Reflectance spectra of slabs (green) and granular ices (red) made of two different brines containing water and 12.5wt% of MgCl2. Figure 1 shows a comparison and evolutions between slabs (green) and granular ice (red) in the case of MgCl2. These samples have been produced from initial brines with 12.5wt% MgCl2. The differences observed between these spectra are in part due to the particles themselves, in terms of size as well as their production process, generating different hydrated phases and in different proportions. Irradiated Ices: F and M-centres are well-known defects in alkali halides crystals [15], formed through electrons replacement in crystal lattice. Due to the coloration induced by this effect, the relevance of this process for the surface of Europa has been strongly suggested [8, 9]. We irradiated salty ices with energetic electrons of 1 and 5 keV, for 15 minutes. Generating a deposition of 1016 e-/cm2, equivalent of weeks to months at the surface of Europa. The ices were produced either from liquid solutions with different concentrations of NaCl (5, 10 and 30wt%) in intimate mixture or as inter-mixture (salt and water ice particles are mixed at solid state [10]). Figure 2 shows the different spectra of salty ices after e- irradiations; normalized at their reflectance value at 0.395 nm. The variations showed from one sample to another are due to their production procedure. The grain size, the concentrations in salt and the mixing process of water ice and salt (hydrated or not) are all playing a role in the resulting alteration of the analogue and will be detailed at the conference. Figure 2: Reflectance spectra of irradiated ices containing 5 10 or 30 wt% of NaCl. Spipa-A and Spipa-B has respectively grains sizes of 4.5±2 µm and 67 ± 31 µm. The orange spectrum is of a non-irradiated ice containing 5wt% of NaCl. The electron irradiation has been conducted at the energy of 1keV, except for the black dot spectra, at 5keV. Summary and Perspectives: This work demonstrates the major influence of the production method on the spectroscopic properties of salty ices prepared as analogues for the surfaces of the icy moons. Simulating irradiation conditions occurring at the surface of the icy moons reveals puzzling differences between the behaviours of different samples. New series of experiments are conducted to understand the systematics behind these behaviours. Once validated, spectral data will be distributed through the DACE and SSHADe platforms (https://dace.unige.ch/lossySearch/ ; https://www.sshade.eu/db/bypass). Acknowledgments: The team from the University of Bern is supported by the Swiss National Science Foundation and through the NCCR PlanetS. References: [1] Ligier, N., et al., (2016), The Astronomical Journal 151. [2] Ligier, N., et al., (2019), Icarus 333. [3] Trumbo, S., et al., (2019), The Astronomical Journal 158. [4] Trumbo, S., et al., (2019), Science Advances 5. [5] Carlson, R. W., et al., (2005), Icarus, 177. [6] McCord, T. B., et al., (2001), Science, 292. [7] Johnson, P. V., et al., (2019), Icarus 321. [8] Hand, K.P., Carlson, R.W., (2015), Geophysical Research Letter. [9] Poston, M. J., et al., (2018), Journal of Geophysical Research: Planets, 122. [10] Pommerol, A., et al (2019), Space Sci Rev 215. [11] Bove, L. E., et al, (2019), Phil. Trans. R. Soc. A 377. [12] Klotz, S., et al., (2009), Nature Materials, Vol.8. [13] Uchida, T., et al, (2010), Phys. Chem. Chem. Phys., 12. [14] Li, D., et al, (2016), CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry 53. [15] Seitz, F., (1946), Review of modern physics, Vol.18 – number 3. .

Planet surfaces exposed to high energy plasma undergo surface alteration by sputtering (e.g., [1]). Impinging ions thereby eject particles from the uppermost layers of mineral grains. The effect that sputtering has on surface reflectivity in mid infrared (MIR) is relevant for the interpretation of surface-based spectra as well as future Bepi Colombo MIR spectra. Previous studies have shown that the IR spectrum of a given mixture varies with its porosity, grain size, temperature, emergence angle and mineral to glass ratio [2, 3, 4, 5, 6]. This study uses the mineral diopside (CaMgSi2O6), enstatite (Mg2Si2O6), wollastonite (Ca2Si2O6), and bytownite (Na0.2Ca0.8Al2Si2O8) as analogues for the surfaces of Moon and Mercury. The minerals were ground to flocculation resulting in mean grain sizes of 20-34 µm and then and pressed into pellets with porosities of about 20 %. In addition to bulk powder pellets, wollastonite powder fractions of 2+ with solar wind characteristic energies of 4 keV under an incident angle of 45°. Before ion irradiation, MIR spectra show an expected, strong dependence on grain size (Figure 1, e.g., [3]). First results of irradiated wollastonite bulk powder pellets with mean grain sizes of 34 µm are presented in Figure 2. IR reflectivity after irradiation shows changes in relative peak intensities and the apparent loss of peaks. A similar effect was observed when lowering grain size in the non-irradiated samples. These results suggest that solar wind sputtering effects add to the ambiguity for interpreting MIR data of planetary surfaces. List of References [1] Pieters, C. M., Noble, S. K. (2016). J. Geophys. Res.-Planet, 121(10), 1865–1884. [2] Salisbury, J. W., Eastes, J. W. (1985). Icarus, 64(3), 586–588. [3] Mancarella, F., et al. (2015). Planet. Space Sci., 117, 96–105. [4] Varatharajan, I., et al. (2019). Earth and Planetary Science Letters, 520, 127–140. [5] Maturilli, A., et al. (2016). Earth Planets Space, 68(1), 84. [6] Young, C. L., et al. (2019). Icarus, 321, 71–81.

AbstractPlanets and other objects in the solar system are exposed to a stream of ions originating from the sun, the solar wind. It has sufficient energy to alter the surface of airless bodies like Mercury via sputtering processes and may create a tenuous exosphere of ejected particles surrounding these objects. Knowing the material parameters relevant for sputtering processes is therefore crucial to understand planetary surfaces. Based on previous efforts with a quartz crystal micro balance as catcher, a more flexible system for evaluating sputtering yields of realistic mineral samples was developed. This allows for direct comparison between glassy thin films and mineral pellet samples with varying properties like grain size or porosity.IntroductionIrradiating thin films of material deposited onto Quartz Crystal Microbalances (QCM) is a common technique for determining ion sputtering yields. It allows precise measurements of the samples mass change during irradiation with ion beams [1, 2, 3]. When Pulsed Laser Deposition (PLD) is used for the transfer of sample material onto a quartz, the original sample stoichiometry can often be reproduced [3]. Due to material constraints of the quartz crystals, the temperature during deposition may not exceed 846 K [4], resulting in glassy sample films. It is however desired to irradiate mineral analogue samples, as the number and angular distribution of sputtered particles might be different for crystals and glassy films and depend on the grain size. One way of approaching this is by weighing a bulk sample before and after irradiation [5]. This technique lacks the high precision of QCMs, which allow determining changes of sample mass equal to less than a monolayer of material [1]. An alternative approach is the detection of ejecta, for example with a pressure gauge, or a QCM as catcher [6, 7]. At TU Wien, a technique using a QCM for catching sputtered material (C-QCM) was developed earlier, showing the ability to determine sputtering yields from bulk samples with such a method [7]. However, this previous setup was limited in its geometry, with the C-QCM placed on a linear manipulator. In this setup, determining the angular distribution of sputtered material required changing distance and tilt angle between sample and C-QCM.New setup for angular resolved measurementsIn the new setup, the sample is mounted on a rotatable holder, which allows for an angular resolved investigation of sputtering yields (angle α in Figure 1). The C-QCM is mounted on a second sample holder and the angle αC between both can be varied independently from α. Sample and C-QCM are placed coaxial, which guarantees a fixed distance and a variable tilt angle. This is of advantage, as the distance dependence of the C-QCM signal follows an inverse-square law and can therefore significantly increase the measurement uncertainty.Figure 1: Principle of the Measurement using a QCM as a catcher. The distance can be kept constant while the angles sample/ions α and sample/C-QCM αC are varied.For the irradiation experiments, ions with solar wind velocity of 440 km s-1 [8] are generated in an Electron Cyclotron Resonance ion source. They are then guided towards the sample holder using electromagnets and electrostatic lenses [9].To avoid charging up of the insulating mineral pellets, the setup is also equipped with an electron flood gun. It delivers electrons with an energy of about 30 eV and is pointed towards the irradiated area, neutralizing the positive charge otherwise accumulating on the sample.The sample holder is equipped with an ohmic heater and a K-type thermocouple. Combined with a Quadrupole Mass Spectrometer, not only irradiations at different sample temperatures, but also Thermal Desorption Spectroscopy (TDS) measurements after irradiations are possible. These can give important information about the implantation and diffusion of solar wind ions in minerals.A QCM thin film sample and a pellet sample can be installed into the experimental chamber at the same time. Both mounts are placed in the same plane which is on the axis of rotation. By moving between both samples with the help of a linear feedthrough, C-QCM signals can be compared directly as the geometry stays the same. This has the additional benefit, that sputtering yields of the thin film sample can be directly evaluated and used for calibration.This new setup allows investigation of sputtering yield and angular distribution for a wide variety of realistic samples. Effects of grain size, surface roughness and porosity on sputtering can be studied and compared with simulations [10] to get a more complete picture on sputtering processes on Mercury's surface.References[1] Hayderer G., et al.: A highly sensitive quartz-crystal microbalance for sputtering investigations in slow ion–surface collisions, Rev. Sci. Instrum., 70, 3696, 1999.[2] Hijazi H., et al.: Kinetic and potential sputtering of an anorthite-like glassy thin film, J. Geophys. Res. Planets, 122, 1597, 2017.[3] Szabo P. S., et al.: Solar wind sputtering of wollastonite as a lunar analogue material – Comparisons between experiments and simulations, Icarus, 314, 98, 2018.[4] Cook R. K., et al.: Piezoelectric constants of alpha-and beta-quartz at various temperatures, Phys. Rev., 80, 712, 1950.[5] Goschnick J., et al.: Sputter yields and erosion rates for low energy ion bombardment of multielemental powders, Nucl. Instrum. Methods Phys. Res. B, 83, 339, 1993.[6] Galli A., et al.: Surface charging of thick porous water ice layers relevant for ion sputtering experiments, Planet. Space Sci., 126, 63, 2016.[7] Berger B. M., et al.: Sputtering measurements using a quartz crystal microbalance as a catcher, Nucl. Instrum. Methods Phys. Res. B, 406, 533, 2017.[8] Wurz P., et al.: Self-consistent modelling of Mercury’s exosphere by sputtering, micro-meteorite impact and photon-stimulated desorption, Planet. Space Sci., 58, 1599, 2010.[9] Dobes K., et al.: Transient effects during sputtering of aC: H surfaces by nitrogen ions, Nucl. Instrum. Methods Phys. Res. B, 286, 20, 2012.[10] Stadlmayr R., et al.: Sputtering of nanostructured tungsten and comparison to modelling with TRI3DYN, J. Nucl. Mater., 532, 152019, 2020.

Experimental quantification of sputtering of planetary surface analogs provides important constraints for the understanding of space weathering [1]. Whereas the Moon and Mars are mostly irradiated by solar wind ions, the Martian moon Phobos is also exposed to atmospheric ions that escape from Mars [2]. In the Martian tail region O+ and O2+ ions at energies of several 100 to several 1000 eV are the predominant contribution to the sputtering of the surface of Phobos [3].Validating and improving such models requires a more detailed experimental investigation of sputtering with relevant analog samples. Therefore, sputtering experiments with O+, C+, O2+ and CO2+ were performed with energies from 1 to 5 keV, corresponding to energies relevant for Martian ions [4]. Augite (Ca, Mg, Fe)2Si2O6 mineral samples were chosen as a Phobos analog since their elemental composition is close to the current understanding of the composition of Phobos’ surface [5]. Thin films were deposited from augite onto Quartz Crystal Microbalances (QCM), which allow in-situ measurements of sputtering yields [6]. SDTrimSP simulations with established input parameters for augite were performed to compare the simulation outcomes with experimental results [7]. Figure 1 Sputtering yields of 2 keV (blue) and 5 keV (orange) O+ ions under different angles of incidence. Experimental values (dots) are compared to SDTrimSP (dashed lines) and SRIM simulations (dotted lines). Measured mass changes during O+ and C+ irradiation are slightly smaller than predicted by the SDTrimSP sputtering simulation, which indicates implantation of projectile ions into the samples (for O+ results, see Figure 1). SRIM simulations are known to overestimate sputter yields for such samples, as is also observed here. Measurements with O2+ and CO2+ show no indication of molecular effects. Their behavior is thus equivalent to sputtering by the sum of their atomic constituents at the same velocity. Figure 2 Calculated ratio of sputtering by atmospheric O ions and solar wind ions. The result from Nenon et al. (blue dashed line) is compared to rescaled calculations on our new experimental data for sputtering by O ions (red line). For the sputtering of the surface of Phobos, the new experimental results support previous assumptions that only O+ and O2+ ions have to be considered. The sputtering by CO2+ ions is most likely negligible. Regarding the O ions, the new experimental results suggest lower sputtering yields by about 50%. Nevertheless, sputtering in the Martian magnetotail region will still be dominated by atmospheric O ions, as previously calculated (Figure 2) [2, 3]. Over the whole orbit of Phobos, our results predict that atmospheric O ions account for 10 to 15% of the sputtering of Phobos’ surface. List of References[1] B. Hapke, J. Geophys. Res.: Planets 106, 10039 (2001).[2] A.R. Poppe, S.M. Curry, Geophys. Res. Lett., 41, 6335 (2014).[3] Q. Nenon, et al., J. Geophys. Res.: Planets 124, 3385 (2019).[4] P.S. Szabo, et al., submitted to J. Geophys. Res.: Planets (2020).[5] F. Cipriani, et al., Icarus 212, 643 (2011).[6] G. Hayderer, et al., Rev. Sci. Instrum. 70, 3696 (1999).[7] A. Mutzke, IPP-Report 2019-02 (2019).

The surfaces of Jupiter's icy moons are continually irradiated by charged particles from the Jovian plasma environment. This irradiation triggers chemical reactions in the surface ice and also acts as an atmospheric release process. Remote observations, theoretical modelling, and laboratory experiments must be combined to understandthis plasma-ice interaction. Here, we present new experiment results concerning the chemistry of irradiated water ice samples relevant for icy moons and other icy objects in the solar system. Introduction The University of Bern is developing the neutral gas mass spectrometer for ESA's Jupiter Icy moons Explorer (JUICE, Grasset et al. 2013), planned to reach the Jupiter system in 2029. We therefore strive to fill knowledge gaps about the basic physics of the surfaces and atmospheres of Jupiter’s icy moons before the arrival of JUICE. We combine the available facilities for developing and calibrating mass spectrometers and ion/electron spectrometers (Marti et al. 2001) with the sample preparation techniques and diagnostics of the Planetary Imaging Group (Pommerol et al. 2019). Experiment setup To study the effects of electrons irradiating water ice, we subjected a variety of ice samples (thin amorphous ice films and macroscopic samples of porous ice with customizable grain size) to an electron beam of energies between 200 eV and 10 keV at pressures and temperatures representative for the surfaces of Jupiter's icy moons. The physical and optical properties of these macroscopic ice samples make them realistic analogues for planetary surfaces beyond the ice line. The effect of chemical impurities in the water ice, such as NaCl, can also be investigated. The particles released from the ice were monitored with a newly designed time-of-flight (TOF) mass spectrometer and (in the case of the water ice film) with a microbalance. Preliminary results Electron irradiation of pure water ice results mostly in the creation and release of H2 and O2 from H2O in a stoichiometric 2:1 ratio, which is in agreement with the results based on an older quadrupole mass spectrometer (Galli et al. 2018). This seems to hold true for any type of water ice sample, independent of grain size and crystallinity. We also derive upper limits for rare radiolysis products (such as OH and H2O2) and the time scales for the build-up and release of radiolysis products. The O2 release lags behind the immediate H2 release by typically ~ 10 s and is reminiscent of the time-dependent sputtering yield of O2 from water ice upon ion irradiation (Teolis et al. 2005). This delayed O2 release has implications for the O2/H2O ratio observed at the surface of icy objects in the solar system, such as Ganymede, Europa, Callisto (Calvin et al. 1996, Spencer and Calvin 2002), and 67P/Churyumov-Gerasimenko (Bieler et al. 2015).