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

Achondrite meteorites have anomalous enrichments in S-33, relative to chondrites, which have been attributed to photochemistry in the solar nebula. However, the putative photochemical reactions remain elusive, and predicted accompanying S-33 depletions have not previously been found, which could indicate an erroneous assumption regarding the origins of the S-33 anomalies, or of the bulk solar system S-isotope composition. Here, we report wellresolved anomalous S-33 depletions in IIIF iron meteorites (<-0.02 per mil), and S-33 enrichments in other magmatic iron meteorite groups. The S-33 depletions support the idea that differentiated planetesimals inherited sulfur that was photochemically derived from gases in the early inner solar system (<similar to 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.