When wet meets dry: An Ivuna-like impactor triggered volatile loss on the angrite parent body
2026-05-29
Angrite meteorites remain the “driest” known planetary materials in the Solar System. Recent mineralogical and oxygen (O) isotope data suggest that the angrite parent body (APB) experienced a major impact, raising questions about the identity of the impactor. We report high-precision mass-independent chromium (ε 54 Cr) isotope data for eight angrites and their components. Samples from deeper APB regions exhibit uniform ε 54 Cr values (−0.40 ± 0.03), representing the mantle composition, whereas matrix materials from quenched angrites show anomalous ε 54 Cr values (0.27 ± 0.06 and −0.15 ± 0.08), likely reflecting impactor contamination. Combined Cr-O isotope data point to a CI (Ivuna-type) chondritic impactor—the “wettest” known Solar System material. Although such an impact could introduce volatiles, high-energy conditions likely caused extensive volatile loss, preserving the angrites’ dry nature. CI contamination may also make quenched angrites unsuitable time anchors for siderophile short-lived chronometers, whereas the other “contamination-free” angrites yield a precise age of 4561.0 ± 0.9 million years, dating the formation of their mantle source.