Sulfur geochemical evidence for a high-energy impact lunar origin

The chemical behavior of sulfur (S) offers a sensitive record of the high-temperature processes that shaped the early Earth–Moon system. Recent advances in constraining the lunar sulfur content and primitive sulfur isotopic composition ¹ (δ ³⁴ S) prompt a reassessment of its implications for Moon formation. Here, we model the coupled evolution of lunar sulfur abundance and isotopic composition across a range of giant-impact scenarios, accounting for disk composition ^2,3 , condensation and vaporization, metal–silicate partitioning ⁴ , and late accretion ⁵ . We show that the canonical Moon-forming impact ² , which involves re-equilibration between metal and silicate in the post-impact disk, predicts excess sulfur and fractionated δ ³⁴ S values in the Moon—both inconsistent with lunar compositions. In contrast, a high-energy giant-impact scenario (e.g., a Synestia) ³ , involving metal exsolution from cooling silicate fluids, yields a sulfur-depleted Moon with δ ³⁴ S values that match current constraints. These results require metal–silicate equilibration at 2,600–3,900 K, supporting a high-temperature origin of the Earth-Moon system. Our findings further suggest that a substantial metal phase may not be required in the initial lunar disk to explain the Moon’s core, thereby relaxing a key constraint embedded in prior giant-impact models ² .