Northwest Africa 8409: Hydrogen Abundance and Isotope Composition in the Mercury-Like Meteorite

Over the past decade, a number of studies have measured a range of achondrites and primitive achondrites from the non-carbonaceous (NC) region to quantify the water abundance of parent bodies that accreted in the inner Solar System, as well as to infer their hydrogen isotopic composition (dD signatures) [e.g., 1-3]. The aim of such studies is to answer one of the greatest unknowns in cosmochemistry, i.e., the source of water in inner Solar System planetesimals. So far, most NC achondrites present a similar dD value of about -300 to -250‰ [e.g., 1-3]. Because most NC achondrites might have formed at or beyond the snowline [4], it is difficult to conclude whether the main source of water could have been water ice (e.g., mantling chondrules) similar to how CM chondrites acquired water [5], or if their hydrogen was somehow acquired (in an isotopically fractionated way) from H gas in the nebula [e.g., 6]. Northwest Africa (NWA) 8409, paired with NWA 7325, could be a key witness in the search for the H source in the innermost region of the Solar System. NWA 7325/8409 is a unique reduced, FeO-poor gabbroic achondrite [e.g., 8]. NWA 7325/8409 was initially proposed to sample Mercury, yet this has been discredited due to its ancient crystalisation ages. However, the possibility that it derived from a Mercury building block cannot be ruled out [9]. Here, we analysed hydrogen abundance and isotope composition of nominally anhydrous minerals (NAMs) in NWA 8409 to better understand the source of water in bodies in the innermost region of the Solar System.