Speaker: Dr. Hairuo Fu
Affiliation: EPSS, UCLA
Date: Wednesday, September 30, 2026
Time: 12:00 PM
Abstract
How the Earth-Moon system formed remains an open question. Although mass-independent isotopic anomalies are widely used to investigate the Moon’s origin, multiple competing giant-impact models can reproduce the observed isotopic similarity, limiting its power to distinguish among them. Here, we ask whether the observed Earth-Moon refractory-element similarity can provide an additional, potentially stronger test. For the first time, we combine 2-D, two-phase-flow geodynamic models of magma-ocean differentiation in the proto-Earth and Theia (the hypothesized Moon-forming impactor) with simulations of the impact itself, tracking how material from different parts of both bodies enters the Moon-forming disk. We find that both bodies can undergo substantial silicate differentiation on timescales relevant to the giant impact, developing internal chemical heterogeneity that is continually reshaped by mantle convection. Because a canonical impact mainly samples their shallow mantles, the predicted lunar composition changes substantially with impact timing. Yet across a wide range of timings, the resulting Moon remains chemically distinct from what we observe. These results suggest that reproducing the Earth-Moon compositional similarity likely requires extensive early post-impact mixing, as may occur in an Earth-Moon synestia formed by a high-energy giant impact.
About the Speaker
Hairuo Fu is an isotope geochemist, geodynamist, and paleomagnetist whose research focuses on the origins and evolution of planetary bodies. He earned a B.S. in Geology from China University of Geosciences (Beijing) in 2016 and a Ph.D. in isotope geochemistry from Harvard University in 2024. He held a LunaSCOPE Postdoctoral Fellowship at Brown University from 2024 to 2026 and is currently working with Peng Ni in the PTXRt Lab at UCLA (2026–2027). He will join the Department of Earth, Environmental, and Planetary Sciences at the University of Tennessee, Knoxville, as a Gerald D. Sisk Assistant Professor. Hairuo combines high-precision isotope measurements with numerical modeling to investigate how elements and isotopes behave during high-temperature processes and what they reveal about planetary evolution. His work spans giant-impact events, planetary differentiation, mantle–crust evolution, and planetary reorientation. He is committed to bridging physical and chemical perspectives on planetary evolution, an approach he views as essential for advancing planetary science. His recent research interests include integrating isotope systematics with geophysical and geodynamic models to constrain the Moon’s bulk composition and proto-lunar disk conditions, test Moon-forming giant-impact scenarios, and probe the compositional structure of the primordial lunar and Martian interiors.