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

Volatile element abundances vary significantly 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 non-carbonaceous reservoirs, indicating insignificant
contribution of outer solar system materials to 4-Vesta's volatiles.
Additionally, 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.