Sulfuric acid as a corrosive cryofluid and oxygen isotope reservoir in planetesimals
Akihiko Hashimoto, Yuki Nakano
In Press, Journal Pre-proof, Available online 25 March 2023
“The Earth-Moon and other planetary objects are enriched in the heavier isotopes, 17O and 18O, relative to 16O by several %, compared to the Sun. A stunning exception is the magnetite/sulfide symplectite found in Acfer 094 meteorite, which shows 24% enrichment in 17,18O. Here we show that the SO and SO2 molecules in the molecular cloud, ~106% enriched in 17,18O relative to the Sun, evolved through the protoplanetary disk and planetesimal stages to become a sulfuric acid, 24% enriched in 17,18O. The sulfuric acid provided a cryofluid environment in the planetesimal and by itself reacted with ferric iron to form an amorphous ferric-hydroxysulfate-hydrate, which eventually decomposed into the symplectite by shock. We indicate that the Acfer 094 symplectite and its progenitor, sulfuric acid, is strongly coupled with the material evolution in the solar system since the days of our molecular cloud.
We interrogate a petrographic relationship of the symplectite to the Acfer 094 meteorite matrix for an additional clue to its origin. In light of the comparative study of Acfer 094 with other “primordial” chondrites that contain amorphous silicate matrices and with GEMS, we conclude that the cryofluid condition was critical to the formation of the Acfer 094 symplectite.”