Félix Vayrac

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).

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.