Rapid accretion of enstatite chondrite (EH)-like embryo as impactors for the proto-Earth

Enstatite chondrites (ECs) exhibit isotopic compositions closely align with the Earth, rendering them indispensable reference for deciphering the building blocks of our planet. Impactors with ECs-like compositions, key contributors to proto-Earth, were proposed to have underwent differentiation. However, such differentiation poses a formidable challenge given the small size of these impactors and the lack of gravity-driven permeable flow, and the high melting temperature of enstatite. Here, we present high-pressure melting experiments on EH3 chondrite, complemented by three-dimensional X-ray computerized tomography analyses of metal segregation under various conditions. Thermodynamic simulations on the temperature evolution of EH chondrite-like embryos reveal that heat produced by radioactive decay systems (²⁶Al, ⁶⁰Fe and ⁴⁰K) is sufficient to melt more than 20% of the silicate components, thus driving metal-silicate segregation only if these embryos accreted early (within 1.1 Myr post-CAI). Such embryos could have attained sizes comparable to the Moon. In contrast, the parent bodies of EH chondrites formed relatively late (1.88–2.0 Myr post-CAI), with radii between 125 and 170 km. Our findings provide pivotal insights into the accretion timing, differentiation mechanisms, and structural characteristics of EH chondrite-like embryos in the early Solar System, addressing a long-standing gap in our understanding of terrestrial planet formation.