The origin of 4-Vesta’s volatile depletion revealed by the zinc isotopic composition of diogenites

Abstract

Volatile element abundances vary substantially among terrestrial planetary bodies like Earth, Mars, Moon, and differentiated asteroids, leading to intense debate about the governing processes. howardites-eucrites-diogenites (HED) meteorites, most likely from asteroid 4-Vesta, represent highly volatile-depleted Solar System samples, offering critical insights into these processes. Zinc is a moderately volatile element and its isotopic composition reveals sources of volatiles in planetary bodies. Our study finds Zn isotopic anomalies in diogenites overlapping with noncarbonaceous reservoirs, indicating negligible contributions of outer solar system materials to 4-Vesta’s volatiles. Besides, zinc isotopic composition of 4-Vesta is lighter than that of chondrites, contrary to the expected signature of evaporation-based volatile depletion. This suggests that after 4-Vesta lost all its volatiles through evaporation during the magma ocean stage, partial kinetic recondensation occurred that produced the observed isotopically light composition. These insights, combined with previous data, underscore the process of global evaporation followed by partial condensation as a key factor influencing the final volatile budget of planetary bodies.