Guillaume Avice

The bonding potential of noble gases in high-pressure silica-bearing solids and melts remains debated, yet it is a central question for understanding their retention behavior and evaluating the role of silicate-bearing phases in the transport and storage of noble gases originally present in the atmosphere. Here, we assess the chemical behavior of noble gases in three silicates: quartz, seifertite, and perovskite. Using the electron localization function and Bader charge analysis, we find no evidence of stable covalent or ionicbonding. The very slow intracrystalline diffusion of heavy noble gases governs their trapping in silicates during crystal growth. Noble gases are more likely to reside in melts or grain boundaries than in silicate crystal lattices.

We investigated the relationship between microporosity, impact deformation, and aqueous alteration in the CM chondrite Murchison using high-resolution (1.86 μ m/voxel) X-ray computed tomography (XCT) combined with a pressurized xenon gas infiltration technique (Xe-XCT). Fine-grained rims (FGRs) around chondrules generally have higher microporosity than the surrounding matrix but display systematic porosity reductions in the direction of impact. This porosity reduction signature is asymmetric, with the lowest-porosity FGR regions clustering along a direction consistent with the inferred impact vector. As predicted by numerical simulations of impacts into bimodal (solid chondrule and porous matrix) material, higher-porosity regions occur on the inferred lee (protected) side of chondrules relative to the impact direction. Elemental mapping using scanning electron microscopy and energy-dispersive X-ray spectroscopy reveals that microporosity is moderately positively correlated with Mg/Fe ratio and strongly negatively correlated with S content, and only weakly negatively correlated with Ca abundance. These relationships indicate that impact-generated microporosity gradients influenced post-impact fluid flow at scales of ∼25–600 μ m, promoting serpentinization and tochilinite breakdown in high-porosity regions. The weaker porosity–carbonate correlation suggests that most carbonates formed prior to impact. Our findings are consistent with numerical models predicting limited (tens to hundreds of microns scale) open-system fluid flow in low-permeability CM chondrites and demonstrate that impact-driven microporosity modification played a key role in controlling subsequent aqueous alteration on the CM parent body.

Sample return missions play a significant role in planetary science by providing pristine extraterrestrial materials. JAXA's Hayabusa2 and NASA's OSIRIS‐REx missions have returned samples from the C‐type asteroids Ryugu and Bennu, respectively. The chemical and mineralogical compositions of these samples closely resemble those of CI chondrites, the traditional reference material for solar system abundances. Based on the findings of the Hayabusa2 mission, JAXA launched the Ryugu Reference Project (RRP) to maximize the scientific value of the returned samples and formed the RRP Measurement Definition Team (RRP‐MDT) to elucidate the RRP's scientific goal and objectives. The RRP‐MDT defined the goal of RRP to reassess the elemental abundances and isotopic compositions of the solar system through comprehensive analyses of the returned asteroid samples and CI chondrites. To this end, the team recommended preparing homogeneously powdered Ryugu reference materials (RRM) using approximately 750 and 400 mg of samples from Chambers A and C, respectively, to address observed compositional heterogeneities. The team proposed to measure the elemental abundances and isotopic compositions of the RRM by analytical techniques involving seven specific measurement groups. Through comprehensive analytical methodologies, interlaboratory calibration, and statistical evaluation, the RRP aims to refine our understanding of solar system formation and evolution.

Origine et évolution du xénon et des autres gaz rares atmosphèriques : implications géodynamiques et atmosphériques: L'origine de l'atmosphère terrestre demeure énigmatique. De plus, de nombreux évènements tels que les contributions de matière extraterrestre, le dégazage de la Terre solide ou encore les fuites de l'atmosphère vers l'espace ont modifié la composition de l'atmosphère au cours du temps. Ces travaux de thèse visaient à analyser précisément la composition de l'atmosphère ancienne piégée dans des roches âgées de plusieurs milliards d'années afin de mieux contraindre son origine et son évolution. L'analyse des isotopes du xénon, un gaz rare, démontre qu'une fraction de l'atmosphère terrestre ne peut avoir été apportée par les météorites mais plutôt par des corps riches en eau et en éléments volatils tels que les comètes. De plus, la composition isotopique de l'atmosphère a évolué au cours du temps jusqu'à il y a deux milliards d'années environ. Cette évolution du fractionnement est peut-être concomitante à celle l'oxygénation progressive de l'atmosphère qui a permis le développement de la vie telle que nous la connaissons aujourd'hui.

Terrestrial planets are located in the inner region of the solar system, where the temperature was too high for water and highly volatile elements to condense. Nevertheless, the Earth contains a sufficient amount to harbor life, but the origin is still debated (carbon-rich meteorites, comets, enstatite chondrites [1-4]). The Hayabusa2 spacecraft (JAXA) collected samples from the C-type asteroid (162173) Ryugu, providing a unique opportunity to improve our knowledge on the origin and distribution of volatile elements. Recent studies on Ryugu and Bennu samples (OSIRIS-REx, NASA) revealed strong similarities with CI-type chondrites [5-9]. A recent study by [7] reported noble gas measurements on three Ryugu samples and revealed, for the C0209 sample, an extreme enrichment in Xe compared to other cosmochemical components accompanied by a strong mass-dependent fractionation of unprecedented magnitude (39.2 ‰/amu) in favor of the heavy isotopes relative to the light ones (Xe-X (P7)). We measured the elemental and isotopic composition of noble gases, released by laser heating steps, of two among the six attributed samples of asteroid Ryugu from Chamber A : A0527 (0.8 mg) and A0532 (0.7 mg), with the aim to check the presence of the new Xe component [7], in order to understand if it is unique to sample C0209 or common in pristine C-rich material. The xenon isotopic composition displays a mixture dominated by Xe-Q [10] plus solar wind and Xe-HL, with no evidence for the presence of Xe-X [7]. Xe-HL typically displays a balanced excess (from the p- and r-process) in light and heavy xenon isotopes relative to the Q phase. Interestingly, in these samples, there is a depletion in light xenon isotopes and an excess in heavy isotopes relative to Q. The excess cannot be purely attributed to fission, requiring contribution from the r-process. The depletion in light Xe isotopes cannot be explained by an atmospheric contamination. Such results induce an imbalance of p- and r-process in primitive asteroid material [5-9] and a heterogeneity in the spatial distribution of presolar component in the solar system or that the light xenon isotopic composition of the phase Q was overestimated in the past. The fact that the results do not show evidence for a contribution from the Xe-X component indicates a possible heterogeneity in terms of noble gas abundance and isotopic composition. Measurements of four other samples from Chamber A are ongoing.[1] Marty 2012. EPSL 313-314:56-66. [2] Marty et al. 2016. EPSL 441:91–102. [3] Marty et al. 2017. Science 356:1069-1072. [4] Piani et al. 2020. Science. 369:1110-1113. [5] Okazaki et al. 2022. Science 379, eabo0431. [6] Broadley et al. 2023. GCA. 345:62-74. [7] Verchovsky et al. 2024. Nat. Comm. 15:8075. [8] Barnes et al. 2025. Nat. Astro. [9] Marty et al. 2025. MAPS. [10] Busemann et al. 2000. MAPS 35:949-973This work was financially supported by CNES (project Hayabugaz) and received funding received funding from the European Research Council (ERC) under the European Union’s Horizon Europe Research and Innovation Program (Grant Agreement 101041122 to Guillaume Avice).

Volatile elements are essential for life development and planetary evolution. However, the timing of their delivery to terrestrial planets remains unclear. Sulfur, selenium, and tellurium are volatiles, but also siderophile elements. Their abundances in Earth’s mantle can be used to determine whether volatile elements were delivered to Earth during or after the segregation of the core. Here, we experimentally measured their partition coefficients between core-forming metal and mantle silicate under pressure, temperature, and oxygen fugacity conditions relevant to a deep magma ocean. Our results show that these elements exhibit similar partitioning behaviors, indicating that core-mantle equilibrium preserves their chondritic relative abundances. If a volatile-rich late veneer has been delivered to Earth after core segregation, it must have been limited in mass, making up a maximum of 0.1% Earth’s mass. This suggests that volatile elements, including water, were accreted continuously during Earth’s growth rather than being delivered predominantly by a late veneer of volatile-rich material such as carbonaceous chondrites.

Early planetary degassing and atmospheric escape are two major, yet unconstrained, processes that shaped early Earth. Modeling predicts that the atmospheric ²⁰ Ne/ ²² Ne ratio is sensitive to solar-Ne mantle degassing over geological time. Until the Great Oxidation Event, atmospheric escape progressively depletes the atmosphere in Xe, leaving an isotopic imprint. However, the quantity of xenon in the ancient atmosphere remains largely unknown. In this study, we analyzed noble gases in Archean hydrothermal quartz fluid inclusions and show that a modern atmospheric ²⁰ Ne/ ²² Ne ratio was almost reached 2.7 Ga ago, implying intense mantle degassing during the first 1.7 billion years of Earth’s history, three orders of magnitude higher than today. Furthermore, we determine an Archean atmospheric Xe/Kr ratio, 2.3 times higher than today, consistent with models of Xe depletion over time through atmospheric escape.