¹Thomas J. Barrett, ¹James F.J. Bryson, ²Kalotina Geraki
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2025.116588]
¹Department of Earth Sciences, University of Oxford, Oxford OX1 3AN, UK
²Diamond Light Source, Harwell Science and Innovation Campus, Didcot OX11 0DE, UK
Copyright Elsevier

Despite being pivotal to the habitability of our planet, the process by which Earth gained its present-day hydrogen budget is unclear. Due to their isotopic similarity to terrestrial rocks across a range of elements, the meteorite group that is thought to best represent Earth’s building blocks is the enstatite chondrites (ECs). Because of ECs’ nominally anhydrous mineralogy, these building blocks have long been presumed to have supplied negligible hydrogen to the proto-Earth. However, recent bulk compositional measurements suggest that ECs may unexpectedly contain enough hydrogen to readily explain Earth’s present-day water abundance. Together, these contradictory findings mean the contribution of ECs to Earth’s hydrogen budget is currently unclear. As such, it is uncertain whether appreciable hydrogen is a systematic outcome of Earth’s formation. Here, we explore the amount of hydrogen in ECs as well as the phase that may carry this element using sulfur X-ray absorption near edge structure (S-XANES) spectroscopy. We find that hydrogen bonded to sulfur is prevalent throughout the meteorite, with fine matrix containing on average almost 10 times more Hsingle bondS than chondrule mesostasis. Moreover, the concentration of the Hsingle bondS bond is linked to the abundance of micrometre-scale pyrrhotite (Fe1-xS, 0 < x < 0.125). This sulfide can sacrificially catalyse a reaction with H2 from the disk at high temperatures to create H2S, which could be dissolved in adjoining molten silicate-rich material. Upon rapid cooling, this assemblage would form pyrrhotite encased in submicron silicate-rich glass that carries trapped H2S. These findings indicate that hydrogen is present in ECs in higher concentrations than previously considered and could suggest that this element may have a systematic, rather than stochastic, origin on our planet.

^1,2Y. Zheng,^1,2X. Yang,¹M. Valdes,^1,2,3A. M. Davis,^1,2P. R. Heck
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14351]
¹Robert A. Pritzker Center of Meteoritics and Polar Studies, Negaunee Integrative Research Center, Field Museum of Natural History, Chicago, Illinois, USA
²Department of the Geophysical Sciences, University of Chicago, Chicago, Illinois, USA
³Enrico Fermi Institute, University of Chicago, Chicago, Illinois, USA
Published by arrangement with John Wiley & Sons

In this paper, we introduce a method for volume measurement of microparticles that includes scanning electron microscope photogrammetry with 3-D model construction. Our results show that our method limits the volume uncertainty to ±10%, which is a significant improvement compared to previous methods (which likely overestimated volume by 100%–200%). We also discuss how the size, morphology, and porosity of the sample can affect the uncertainty of volume measurement. We find that our method can have a significant impact on cosmic ray exposure age determinations based on noble gas concentration, with implications for our understanding of cosmic ray irradiation of refractory minerals in the early solar system and presolar grains in the interstellar medium.