¹Hisayoshi Yurimoto et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70158]
¹Department of Natural History Sciences/IIL, Hokkaido University, Sapporo, Japan
Published by arrangement with John Wiley & Sons

NASA’s OSIRIS-REx mission delivered pristine regolith samples from the near-Earth carbonaceous asteroid (101955) Bennu, enabling direct assessment of primitive asteroid material free from terrestrial alteration. We report comprehensive analyses of H, C, O, S, Cl, and Hg in Bennu samples using X-ray fluorescence (XRF), thermogravimetric analysis coupled with mass spectrometry (TG-MS), combination analyses of pyrolysis and combustion (EMIA-Step), and direct Hg measurements. Quantification of O, Si, S, Cl, and Ge by XRF is reported for Bennu samples for the first time. TG-MS reveals ~15 mass% total mass loss, with H2O and CO2 release patterns attributed to phyllosilicates, carbonates, and organic matter. Bennu samples contain substantially higher interlayer H2O than those from asteroid Ryugu, consistent with subsurface deeper sampling by OSIRIS-REx. Total carbon abundance is ~4.1 mass%, dominated by organic carbon (~2.9 mass%), comparable to Ryugu samples. Mercury abundances (82–141 ng g−1) are far lower than those reported for CI chondrites, indicating pervasive terrestrial contamination in meteorite samples. We recommend a Hg abundance of 98 ± 2 ng g−1 for Bennu samples and pristine CI-like material, demonstrating that returned asteroid samples provide the most reliable record of primitive carbonaceous matter.

¹Sohei Wada,¹Ken-ichi Bajo,¹Hisayoshi Yurimoto
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70161]
¹Department of Earth and Planetary Sciences, Hokkaido University, Sapporo, Japan
Published by arrangement with John Wiley & Sons

The surfaces of small celestial bodies are continuously modified by spaceweathering and surface gardening, yet their interaction remains poorly understood due toobservational gaps between micrometer and centimeter scales. Here we analyzed thetwo-dimensional distribution of helium in the carbonaceous chondrite NWA 801 (CR2)using the LIMAS secondary neutral mass spectrometer with micrometer resolution. Theresults show that 4He is concentrated mainly in the fine-grained matrix, forming a distinctHe-rich network surrounding He-poor fine-grained regions. This structure suggests thatspace-weathered particles were transported into the subsurface. The process may involve agranular convection driven by impact-induced vibrations. It likely occurred during the earlysolar system on time scales of 10,000 years and at depths ranging from tens of centimetersto meters. Such mixing repeatedly exposed fresh material to solar wind irradiation,producing three-dimensional 3He-enriched deposits rather than purely surface-limitedaccumulations. These findings provide direct microstructural evidence for the dynamiccoupling between space weathering and surface gardening and highlight a potentialmechanism for forming solar wind–derived helium and hydrogen resources on small celestialbodies.