Noah Jäggi

Angular distributions of sputtered ejecta are critical inputs for simulating regolith sputtering on airless bodies, where surface topography and porosity determine if particles escape or redeposit. We present new analysis and simulations demonstrating that, although current binary collision approximation (BCA) frameworks can reliably predict either total sputter yields or angular distributions for minerals, they cannot reproduce both simultaneously. This is a limitation with direct implications for exosphere and surface-evolution models that require realistic, three-dimensional ejecta plumes. Using SDTrimSP[1] for flat targets, SPRAY[2] for AFM-resolved rough surfaces, and SDTrimSP-3D[3] for porous regolith analogs, we quantify how morphology and binding energies control plume tilt and shape via a dedicated three-dimensional lobe-fitting approach designed for full-plume implementation in modeling tools. This framework addresses the need to move beyond simplified cosine laws and to incorporate azimuthal structure when propagating sputtered particles in regolith and exosphere simulations.Across surface morphologies, rough and porous targets deflect ejecta toward the surface normal, reducing the strongly forward-facing plumes typical of flat surfaces and introducing geometry-mediated effects such as shadowing and redeposition that reshape both yield and energy distributions. In this regime, we find a robust tradeoff between reproducing sputter yield and plume tilt: the “compound/hybrid” binding-energy model[4] capable of matching experimental mineral yields[5] fails to reproduce the experimentally observed forward tilt at oblique incidence on flat and, more significantly, on rough surfaces (Fig. 1). Conversely, adopting increased surface-binding energies (SBEs) informed by recent molecular dynamics work[6] strengthens the forward tilt and better matches rough-surface angular data but underestimates absolute mass yields by factors of 3–4.Figure 1: Model–data comparison of sputter yields and angular distributions for MgSiO3 under 4 keV He irradiation. Left: SDTrimSP model yields that result from the Jäggi et al. (2023) hybrid binding energy model (HB-C, blue dashed) with the increased surface-binding case (SB-C) based on Morrissey et al. (2024) surface binding energies, compared to the Biber et al. (2022) laboratory measurements (black, with 2 SD errors). Center: Normalized mass yield polar distributions from a flat surface at an incidence angle αin = 60° for said simulations. Right: Analogous to the center figure, but for a rough pellet surface. Methodologically, we map flat-surface SDTrimSP ejecta to measured roughness via ray tracing in SPRAY and construct porous regolith stacks in SDTrimSP-3D, then fit the resulting plumes with a single- or tri-lobe model that captures central and side “winglet” components associated with single-collision recoils (Fig. 2). This procedure allows for consistent comparison to laboratory angular data and direct use of fitted plumes in forward models. For rough surfaces, the simulations confirm a forward tilt relative to the sample surface normal but with magnitudes that depend sensitively on the binding-energy scheme. Only the higher-SBE case reproduces the observed forward-tilted distributions. For porous targets, preliminary comparisons and prior 3D simulations indicate stronger backscattering, further emphasizing the need for morphology-aware angular inputs in regolith sputtering models.Figure 2: Comparison of O sputter ejecta distributions sputtered from a rough surface (SPRAY) by 4 keV He at an incidence angle of αin = 75° from the surface normal (black arrow) resulting from (left) the Jäggi et al. (2023) hybrid binding energy (HB) model and from (right) a surface binding energy (SB) model with increased binding energies from Morrissey et al. (2024), fitted by a central plume (blue) and two forward-facing “winglet” plumes (red). These findings have two key implications. First, exosphere and regolith models should incorporate full 3D angular distributions rather than rely on simple cosine laws, especially for rough and porous substrates where plume tilt and azimuthal structure are non-negligible. Second, the inability to match yield and angle concurrently suggests missing physics in BCA implementations—most notably, yield-enhancing processes such as molecule and cluster sputtering that are not represented in single-atom BCA ejecta—and cautions against parameter tuning. In practice, our results recommend using binding-energy models that best reproduce angular distributions when plume directionality controls transport and redeposition, while acknowledging that total yields must then be corrected for non-BCA processes if absolute source strengths are required.In summary, angular distribution data are indispensable for realistic regolith sputtering simulations, yet existing BCA parameterizations cannot simultaneously reproduce experimental mass yields and angular distributions across flat, rough, and porous mineral surfaces. This demonstrates a fundamental limitation of current BCA-based models for planetary surfaces and motivates hybrid or extended frameworks that incorporate missing yield mechanisms while retaining accurate, morphology-dependent plume geometry.References[1] Mutzke, A., Toussaint, U. v, Eckstein, W., Dohmen, R. & Schmid, K. (2024). SDTrimSP Version 7.00. Technical Report[2] Cupak, C. et al. Appl. Surf. Sci. 570, 151204 (2021).[3] von Toussaint, U., Mutzke, A. & Manhard, A. Phys. Scr. T170, 014056 (2017).[4] Jäggi, N. et al. Planet. Sci. J. 4, 86 (2023).[5] Biber, H. et al. Planet. Sci. J. 3, 271 (2022).[6] Morrissey, L.S. et al. Planet. Sci. J. 5, 272 (2024).

The development of hollows on Mercury—small depressions with spectrally bright interiors and halos—may have resulted from the selective loss of volatile components in these regions. Proposed mechanisms driving elemental or molecular volatility include intense solar radiation, micrometeoroid impacts, and repeated thermal cycling, which leave behind a refractory layer with distinct spectral properties. We investigate solar wind ions as a potential darkening agent and demonstrate that Mercury-relevant sulfides preserve their high reflectivity.Experimental ion-irradiation studies on sulfides such as NiS, CuS, CoS, FeS, and MoS have shown that metallic surface layers can form through cation segregation and preferential sulfur depletion [1–5]. Laboratory work has further revealed iron enrichment at the surface, accompanied by visible darkening, in troilite (FeS) and more recently in pentlandite [(Fe,Ni)₉S₈] subjected to ion and laser irradiation [e.g., 6, 7]. Unlike lunar, meteoritic, and asteroidal materials, which contain significant iron and nickel sulfide minerals, Mercury’s surface appears depleted in iron. Instead, sulfides are expected to be dominated by Mn, Ti, Cr, Mg, and Ca cations, based on correlations with sulfur detected by MESSENGER’s spectrometer suite [8–10].We have previously shown that the sulfides: niningerite (MgS) and oldhamite (CaS), two phases proposed as likely hollow-forming material based on visible-to-near-infrared (VNIR) spectral analysis [11], are radiation-hard [12]. These sulfides thereby resist the formation of a metallic top layer, observed in ion-irradiated Fe-sulfides, when exposed to solar wind-speed protons and helium ions.Subsequent spectral analysis of the irradiated CaS and MgS showed brightening in parts of the visible range (0.4-0.7 µm) of the VNIR (Fig. 1) and an overall brightening in the mid-infrared (MIR) range observed by BepiColombo (7-14 µm, Fig. 2). The sample labeled as oxidized was exposed to air for months after the experiments, which led to an overall darkening in both VNIR and MIR, erasing the effect of irradiation. On Mercury, there is no immediate oxidation of the top layer; instead, re-deposition of thermal and ion desorbed material introduces surface contaminants, which over geological timespans could form a layer. The radiation-hard nature of sulfides could thereby act as a cleaning mechanism, where contaminants are removed continuously under solar wind exposure without damaging the bulk, preserving the reflectivity of the sample. This process provides a new framework for understanding the formation of bright hollow materials, highlighting the importance of non-transition-metal sulfides in Mercury’s surface evolution. Figure 1: Visual-to-near infrared measurement of fresh MgS (black line) compared to 2 keV protons (salmon) and an old, oxidized sample (yellow). Two unirradiated MgS samples are shown, whereas one is fresh (syn) and one is old and oxidized (old). Figure 2: Mid-infrared measurements of two MgS samples sourced from BenchChem (BC, solid lines) and Zegen Metals & Chemicals (ZMC, dashed lines). The irradiated samples (light gray) have a consistently higher reflectivity than the unirradiated (fresh) samples. The heavily oxidized sample (yellow) is the darkest.

The interactions between micrometeoroid impacts and solar wind on the surface of the Moon remain a major area of investigation in the space weathering field. In this study, we first irradiated Fe-bearing enstatite [(Mg,Fe) ₂ Si ₂ O ₆ ] (1.50 at% Fe) with a nanosecond-pulse UV excimer laser ( λ = 248 nm) to simulate micrometeoroid impacts, using fluences above and below the ablation threshold to produce four different impact-processed regions. Next, we irradiated the surfaces with 4 keV He ⁺ to explore how prior impact processing changes the way solar wind ions interact with mineral surfaces. We performed comprehensive micro-scale to nano-scale characterization of the experimental products using scanning electron microscopy, scanning transmission electron microscopy, electron energy loss spectroscopy, and energy dispersive X-ray spectroscopy. In the samples irradiated above the ablation threshold, we observed the coexistence of nanophase Fe ( np Fe ⁰ ) and Fe ³⁺ -bearing glass, indicating that np Fe ⁰ formation was driven by charge disproportionation. In the sample irradiated at the highest laser fluence, we produced helium-bearing vesicular np Fe ⁰ , an enigmatic space weathering product known to occur widely on the Moon. Finally, we show that the temperature of impact melting and the phases produced by impact processing have a direct influence on the target’s sputtering behavior and overall helium capture capacity. Our findings demonstrate that micrometeoroid impacts play a critical role in modifying the crystal structure and chemistry of regolith grain surfaces and that variation in impact processing can fundamentally shift the subsequent interactions that solar wind ions have with affected surfaces.

The MESSENGER mission revealed unexpectedly high sulfur content within Mercury’s surface, deviating from the lunar regolith, which was until recently considered a good Mercury analog. Mercury’s exposure to energetic space weathering processes suggests that this high sulfur concentration should be reflected in the Hermean exosphere. UV spectroscopy has not yet detected exospheric sulfur, and future detection by BepiColombo’s Mass Spectrum Analyzer depends on the exospheric sulfur abundance. Radiation-induced segregation has been observed in the common sulfide troilite (FeS), where the resulting metal cap is expected to reduce sulfur ejection to Mercury’s exosphere. We investigate the irradiation response of Mercury-relevant niningerite (MgS) and oldhamite (CaS). The sulfides were irradiated with solar wind speed 2 keV H 2 + or 4 keV He ⁺ , and in situ compositional and chemical bond analysis was performed using an X-ray photoelectron spectroscopy microprobe. Neither MgS nor CaS expressed detectable radiation-induced segregation and instead reached metal-to-sulfur ratios close to bulk with irradiation. This agrees with a preexisting stability hypothesis based on the enthalpy of atomization. This hypothesis is, however, not always applicable, although comprehensive and accurate thermodynamic data are lacking. Based on the structural information of sulfides with known irradiation behavior, we inferred that an S–S anionic spacing exceeding ∼3.2 Å inhibits radiation-induced sulfur depletion. We predict no cation surface segregation in Hermean sulfides and no reduction in suprathermal sulfur emission caused by metal cladding formation in Ti, Mn, Cr, and Ca–Mg sulfides. This radiation hardness for Mercury-relevant sulfides is novel and unexpected and should facilitate detection in Mercury’s exosphere by the BepiColombo mission.

The MESSENGER mission revealed unexpectedly high sulfur content within Mercury's surface, deviating from the Lunar regolith, which was, until recently, considered a good Mercury analogue. Mercury's exposure to energetic space weathering processes such as meteoritic impact and solar-wind sputtering suggests this high sulfur concentration should be reflected in the suprathermal sulfur population of the Hermean exosphere. UV spectroscopy has not yet detected exospheric sulfur, a result attributed primarily to its low glow-factor. Future detection by BepiColombo's Mass Spectrum Analyzer depends on sulfur abundance in the exosphere. Radiation-induced segregation has been observed in the common sulfide troilite (FeS), a constituent mineral in returned Lunar samples, meteorites, and asteroids, where the resulting metal cap is expected to reduce sulfur ejection to Mercury's exosphere. In this work, we investigate the irradiation response of Mercury-relevant sulfides. Niningerite (MgS) and oldhamite (CaS) were irradiated with solar-wind speed 2 keV H$_2^+$ or 4 keV He$^+$, and in-situ compositional and chemical bond analysis as a function of fluence was performed using an XPS microprobe. Neither MgS nor CaS expressed detectable damage-induced segregation and instead reached metal-to-sulfur ratios close to bulk with irradiation. Based on this finding, structural information, and literature analyses, we infer that an S-S anionic spacing exceeding $\sim$3.2 Å inhibits radiation-induced sulfur depletion and promotes stoichiometric sputtering. We therefore predict no cation (metal) surface segregation in Hermean sulfides and no reduction in suprathermal sulfur emission caused by metal cladding formation in TiS, CrS, and Ca-Mg sulfides. This radiation-hardness for Mercury-relevant sulfides is novel and unexpected, and should facilitate detection in Mercury's exosphere by the BepiColombo mission.

Important aspects concerning the origin and formation of the Moon’s exosphere, its tenuous gas envelope, remain puzzling with uncertainties regarding the importance of different effects. Two competing processes — micrometeoroid impact vaporization and solar wind ion sputtering — are considered key contributors to the ejection of particles into the exosphere. Here we present direct, high-precision yield measurements of solar wind ion sputtering using real lunar samples (Apollo 16 sample 68501), combined with advanced 3D simulations of regolith erosion. We find solar wind sputter yields up to an order of magnitude lower than previously used in exosphere models. The difference is primarily due to the suppressive effects of surface morphology, in particular the roughness and high porosity of the lunar regolith. Our results provide critical, experimentally validated sputter yield estimates and address long-standing modeling uncertainties. These results are particularly timely in light of upcoming and ongoing missions, such as the Artemis program at the Moon or BepiColombo at Mercury, contributing essentially to our understanding of how the surfaces of rocky bodies in the solar system are altered.

Europlanet is a non-profit association that promotes the advancement of European planetary science and related fields, for the benefit of the community, and is open to individual and organisational members. We are dedicated to creating a diverse and inclusive network that supports planetary science and related fields across Europe and globally. This is the main task of the Eruoplanet Diversity Committee (1, 2).Our main aims are to promote equality, diversity and inclusivity in planetary science and related fields, with a particular focus on our annual meeting, the Europlanet Science Congress (EPSC), and workshops organised through Europlanet and its membership. The Committee members are the diversity officers from all the Europlanet Regional Hubs, in addition to representatives from the Europlanet Early Careers (EPEC) network and the Europlanet Executive Board. This structure enables close links between the Diversity Committee, the Hubs and other Europlanet structures, and ensures that diversity is embedded within all activities of the Europlanet Society. The Europlanet Diversity Committee also coordinates efforts with partner societies globally. We are working with the Professional Culture and Climate Subcommittee of the DPS on diversity efforts for our joint EPSC-DPS 2025 meeting.The Europlanet Diversity Committee supports efforts to foster engagement and collaboration with individuals and institutions from groups and countries that are under-represented in planetary science and to increase awareness of challenges faced within the community. In recent years, mentoring, expert exchanges, training, discounted fees and targeted meetings have all been offered to support diversity and inclusion. We have run annual wiki-edit-a-thons since 2020 to highlight the valuable contributions of women and under-represented groups within the international planetary science community. Since 2011, we have tracked trends in participation by under-represented countries in EPSC to try to better understand the current situation and identify barriers to participation, and craft effective responses to reduce them. We have also offered sessions, round-tables and short courses at EPSC and other Europlanet meetings to support the sharing of best practice and training in areas such as bystander intervention, mental health and wellbeing. In 2025, we plan to run a ‘pulse survey’ to gauge and enhance our members’ engagement, wellbeing, inclusion, and work culture.The Europlanet Science Congress (EPSC) is the annual meeting place of the Europlanet Society and is largest planetary science meeting in Europe. It covers the entire range of planetary sciences with an extensive mix of talks, workshops and poster sessions while providing a unique space for networking and exchange of experiences. For an event with this dimension and importance, it is crucial to think, discuss and improve the diversity, inclusiveness, and accessibility plan of EPSC to enable as wide an access as possible for the entire planetary science community worldwide. This is one of the main tasks of the Europlanet Diversity Committee.The target groups that have been addressed by the Europlanet Diversity Committee are mainly: women, early career participants, researchers from the under-represented European countries, non- EU participants, colleagues with disabilities, people of color, other minorities, and allies. Each year, the Committee organizes various opportunities during EPSC to open a dialogue with the community, to collect their needs and to address solutions.Measures implemented through the activities of Diversity Committee in the venue selection and operation of EPSC include: provision of food suitable for those with various dietary requirements, access to gender neutral washroom facilities, a raising of awareness for conveners regarding implicit bias and the importance of having diverse panel members, and generally normalizing the promotion and discussion of diversity in STEM at academic meetings, offering childcare, to parents with young children, in close collaboration with the Local Organizing Committee (LOC). The provision of a ‘Silent Room’ is now a tradition at EPSC, enabling participants to find refuge from the crowded conference, and offering a private and comfortable space for nursing mothers, prayers, or any other needs requiring isolation for a short time. Accessibility to the venue is always closely reviewed by the LOC and the Diversity Committee. Offering the congress in hybrid mode is another way of ensuring accessibility for those who can’t travel to attend the congress.Exchange with the community and collecting feedback from the individuals are vital to a committee trying to ensure a diverse and inclusive atmosphere. In order to achieve this, we organize an annual Diversity Roundtable, Diversity sessions in the scientific programme, a diversity keynote talk during the ice-breaker on Sunday prior to EPSC, and various types of workshops and training. Feedback from all EPSC participants is also solicited through a form that asks respondents to share their thoughts and comments on what they liked and didn’t like about the meeting, and suggestions for change at future meetings. The summary of these findings are discussed by the EPSC and Diversity Committees to ensure that lessons are learned and the meeting adapts to the needs of the community.The Diversity Committee of the Europlanet Society aims to highlight diversity within the planetary science community and to reduce the gender gap on Wikipedia. Therefore, we have been organizing, in collaboration with Women in Red and WikiDonne, since EPSC 2020, the Planetary Science Wiki Edit- a-thon. An Edit-a-thon (‘edit marathon’) is an organized event where editors from an online community (such as Wikipedia in this case) write, translate and improve articles on a specific topic. During EPSC, we provide basic training to start...

Impacts of solar wind (SW) ions on the Moon contribute to surface hydration, alteration of the lunar surface via space weathering and the emission of atoms into the exosphere via sputtering [1]. Furthermore, scattering of SW protons as H+, H0 (energetic neutral atoms, ENAs) and recently as H- have allowed direct in-situ observations of ion impacts on the surface [2-4]. For example, measurements of scattered particle allow quantifying the shielding efficiency in magnetic anomalies and even the characterization of regolith properties [5,6]. Here we focus on giving an overview of recent work on observations and modeling of ion-surface interaction. In particular, we discuss how ENA emission from H scattering is connected to properties of the solar wind and the lunar surface [6-8]. We will further highlight how these studies allow us to better constrain sputtering of the surface by ion impacts, as well as new modeling studies that help us better describe the sputtering process [9,10]. References[1] P. Wurz, et al., Space Science Reviews 218.3 (2022): 10.[2] M. Wieser, et al., Planetary and Space Science 57.14-15 (2009), 2132.[3] D. J. McComas, et al., Geophysical Research Letters 36.12 (2009).[4] C. Lue, et al., Geophysical Research Letters 38.3 (2011).[5] A. Vorburger, et al., Journal of Geophysical Research: Space Physics 117.A7 (2012).[6] P. S. Szabo, et al., Geophysical Research Letters 49.21 (2022), e2022GL101232.[7] P. S. Szabo, et al., Journal of Geophysical Research: Planets 128.9 (2023), e2023JE007911.[8] S. Verkercke, et al., The Planetary Science Journal 4.10 (2023), 197.[9] N. Jäggi, et al., The Planetary Science Journal 4.5 (2023), 86.[10] L. Morrissey, et al., The Planetary Science Journal 5.12 (2024), 272.

The formation of hollows on Mercury—small, irregular, depressions often surrounded by brighter halos—has been thought to be driven by the preferential loss of volatile components due to intense solar radiation, micrometeoroid bombardment, and thermal cycling, leaving behind a refractory, spectrally distinct layer. One such process is the decomposition of regolith sulfides under solar wind ion irradiation.Previous ion irradiation experimental studies on sulfides such as NiS, CuS, CoS, FeS, and MoS have demonstrated the formation of metallic surface layers through cation chemical segregation and preferential sulfur loss [1-5]. Laboratory observations of Fe surface-enhancement with subsequent visual darkening for ion and laser irradiated troilite (FeS) and recently, pentlandite [(Fe,Ni)9S8], thereby informed the hypothesis that similar process could occur with Mercury-relevant sulfides [e.g., 6, 7]. Instead of FeS, however, Mercury appears depleted in Fe at the surface, and sulfides are expected to contain mostly Mn, Ti, Cr, Mg, and Ca, based on the correlation with sulfur on the planet’s surface as inferred from MESSENGER’s X-Ray Spectrometer (XRS) and Gamma-Ray Spectrometer (GRS) data [8-10].To test if sulfides relevant to Mercury darken under ion irradiation, we focus on MgS and CaS, two sulfides that also were proposed as likely hollow-forming material based on visible-to-near-infrared spectral analysis [11]. Unlike their transition-metal counterparts, these sulfides exhibit irradiation-hardening behavior, resisting the formation of a metallic top layer when exposed to solar wind-speed protons and helium ions [12]. This suggests that their response to space weathering differs fundamentally from that of previously studied sulfides, which also impacts how global exospheric models incorporate sputtered sulfur. Notably, our data reveal that MgS and CaS undergo significant brightening under irradiation in not only the visible-to-near-infrared (VNIR), but also the thermal infrared (TIR) spectral range. This optical alteration for stoichiometrically sputtered sulfide species aligns with the observed reflectance properties of hollows’ bright halos on Mercury.We therefore propose that irradiation-hard sulfides, such as MgS and CaS, could be responsible for the bright spectral signatures surrounding hollows. However, rather than forming metal-rich coatings, these compounds develop radiation-resistant, chemically stable surfaces that enhance reflectance while maintaining their compositional and structural integrity under Mercury’s extreme solar radiation conditions. This mechanism offers a new perspective on hollow bright material formation, emphasizing the role of non-transition-metal sulfides in shaping the planet’s surface evolution.[1] Feng and Chen (1974), J. Phys. C, 7(5), L75[2] Coyle et al. (1980), J. Electron Spectrosc. Relat. Phenom., 20(2), 169–182[3] Loeffler et al. (2008), Icarus, 195(2), 622–629[4] Christoph et al. (2022), J. Geophys. Res. Planets, 127(5)[5] Chaves et al. (2025), Meteorit. Planet. Sci., in process[6] Blewett et al. (2011), Science, 333(6051), 1856–1859[7] Blewett et al. (2013), J. Geophys. Res. Planets, 118(5), 1013–1032[8] Nittler et al. (2011), Science, 333(6051), 1847–1850[9] Weider et al. (2012), J. Geophys. Res. Planets, 117(10), 1–15[10] Weider et al. (2015), Earth Planet. Sci. Lett., 416, 109–120[11] Barraud, Besse and Doressoundiram (2023), Sci. Adv., 9(12)[12] Jäggi et al. (2024), 55 Lunar Planet. Sci. Conf., Abstract #13