Accretion and Differentiation of Vesta and the Mesosiderite Parent Body Inferred From Ni Stable Isotope Compositions

We present high‐precision Ni stable isotope data for mesosiderites, eucrites, and diogenites to investigate the accretion and differentiation of asteroid 4 Vesta. Ni isotope variations in eucrites and diogenites are dominated by kinetic diffusion and chondritic contamination, rendering them unsuitable for reconstructing Vesta's primitive Ni composition. In contrast, mesosiderites yield an average δ60/58Ni value of 0.119 ± 0.044‰ (2SE), representing the bulk and core Ni isotopic signature of Vesta or the mesosiderite parent body. This value is Earth‐like but distinct from those of chondrites, iron meteorites, and ureilites, suggesting diverse precursor materials and Ni isotope heterogeneity in the early Solar System. Results from pMELTS modeling and the olivine‐rich sample MIL 07001 support magma ocean crystallization as a key evolutionary stage on Vesta. Anomalously high δ60/58Ni in the impact‐melt diogenite NWA 5480 likely reflects evaporation, highlighting a possible new application of Ni isotopes as tracers of planetary volatile loss.