Exploring nebular ingassing in the inner Solar System: Evidence from the unique achondrite NWA 8409

The origin of hydrogen in inner Solar System planetesimals remains unknown. Analyses of the hydrogen isotopic composition in non-carbonaceous (NC) chondrites and achondrites can be used as a proxy to determine the origin of this hydrogen. Indeed, the main H reservoirs in the Solar System have distinct isotopic composition. However, NC chondrites and achondrites have yet to reveal the definitive source of their hydrogen. Consequently, it is uncertain whether hydrogen in the parent bodies of these objects originated from outer Solar System sources, such as interstellar ices, or from inner Solar System sources, including nebular gas. The Mercury-like ungrouped achondrite Northwest Africa (NWA) 8409, believed to have formed in the Solar System’s innermost regions, offers the unique opportunity to assess nebular H2 as a potential hydrogen source in planetesimals that formed early and well inward of the snowline. The abundance and isotopic composition of H in nominally anhydrous minerals from NWA 8409 (δD = −560 ± 166 ‰) suggest indeed that nebular gas was the principal source of hydrogen in NWA 8409’s parent body, supporting the hypothesis that nebular ingassing was a viable process in the early and inner Solar System.