Early inner solar system origin for anomalous sulfur isotopes in differentiated protoplanets

Achondrite meteorites have anomalous enrichments in ³³S, relative to chondrites, which have been attributed to photochemistry in the solar nebula. However, the putative photochemical reactions remain elusive, and predicted accompanying ³³S depletions have not previously been found, which could indicate an erroneous assumption regarding the origins of the ³³S anomalies, or of the bulk solar system S-isotope composition. Here, we report wellresolved anomalous ³³S depletions in IIIF iron meteorites (<.0.02 per mil), and ³³S enrichments in other magmatic iron meteorite groups. The ³³S depletions support the idea that differentiated planetesimals inherited sulfur that was photochemically derived from gases in the early inner solar system (<∼2 AU), and that bulk inner solar system S-isotope composition was chondritic (consistent with IAB iron meteorites, Earth, Moon, and Mars). The range of mass-independent sulfur isotope compositions may reflect spatial or temporal changes influenced by photochemical processes. A tentative correlation between S isotopes and Hf-W core segregation ages suggests that the two systems may be influenced by common factors, such as nebular location and volatile content.