Revised metal-silicate partitioning does not require the Late Veneer

Highly siderophile elements (HSEs) are critical tracers for deciphering planetary formation and evolution. The widely accepted Late Veneer hypothesis, which proposes the accretion of chondritic materials after core formation, was developed to explain the discrepancy between metal-silicate partitioning behavior and the HSE composition of the Earth's primitive upper mantle (PUM). However, prior partitioning experiments relied on systems with unrealistically high bulk HSE concentrations, introducing significant uncertainty. Here, we present high-pressure and high-temperature experiments on HSE partitioning across a wide range of bulk HSE concentrations, including conditions relevant to terrestrial planets. Our results demonstrate that HSEs are more soluble in silicate melts at low concentrations and converge to chondritic relative abundances under these conditions, resolving the previous mismatch between mantle HSE composition and PUM. Furthermore, the revised partition coefficients not only reduce the discrepancy for Earth's mantle but also explain the HSE composition of the lunar mantle through core-mantle differentiation processes. These findings challenge the necessity of the Late Veneer for both Earth and Moon, aligning with recent discussions on the volatile element origins of terrestrial planets. This study offers a transformative perspective on the early differentiation and formation of Earth and other rocky planets in the solar system.