New evidence for wet accretion of inner solar system planetesimals from meteorites Chelyabinsk and BenenitraOPEN ACCESS 

Ziliang Jin, Maitrayee Bose, Tim Lichtenberg, Gijs Mulders

accepted for publication in The Planetary Science Journal


Update (28 December 2021): LINK (OPEN ACCESS) / PDF (OPEN ACCESS)
The Planetary Science Journal, Volume 2, Number 6

“We investigated the hydrogen isotopic compositions and water contents of pyroxenes in two recent ordinary chondrite falls, namely, Chelyabinsk (2013 fall) and Benenitra (2018 fall), and compared them to three ordinary chondrite Antarctic finds, namely Graves Nunataks GRA 06179, Larkman Nunatak LAR 12241, and Dominion Range DOM 10035. The pyroxene minerals in Benenitra and Chelyabinsk are hydrated (∼0.018–0.087 wt.% H2O) and show D-poor isotopic signatures (δDSMOW from -444hto -49h). On the contrary, the ordinary chondrite finds exhibit evidence of terrestrial contamination with elevated water contents (∼0.039–0.174 wt.%) and δDSMOW values (from -199h to -14h). We evaluated several small parent body processes that are likely to alter the measured compositions in Benenitra and Chelyabinsk, and inferred that water-loss in S-type planetesimals is minimal during thermal metamorphism. Benenitra and Chelyabinsk hydrogen compositions reflect a mixed component of D-poor nebular hydrogen and water from the D-rich mesostases. 45-95% of water in the minerals characterized by low δD SMOW values was contributed by nebular hydrogen. S-type asteroids dominantly composed of nominally anhydrous minerals can hold 254-518 ppm of water. Addition of a nebular water component to nominally dry inner Solar System bodies during accretion suggests a reduced need of volatile delivery to the terrestrial planets during late accretion.”