¹Hairuo Fu, ¹Stein B. Jacobsen
Earth and Planetary Science Letters 672, 119697 Link to Article [https://doi.org/10.1016/j.epsl.2025.119697]
¹Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA
Copyright Elsevier

Emerging evidence of strikingly similar Earth–Moon refractory lithophile element compositions provides a key constraint on lunar origin, underscoring the need for a novel framework to test competing Moon formation models. Here, we evaluate whether the canonical giant-impact hypothesis can account for this compositional similarity. We model depth-dependent refractory element heterogeneity within the differentiated Moon-forming impactor and proto-Earth and integrate these chemical signatures with the canonical giant-impact sampling to predict the Moon’s composition. Our modeling shows that the canonical model would lead to a highly fractionated proto-lunar disk composition relative toEarth’s mantle and cannot reproduce the observed Earth–Moon similarity, when mantle compositional differentiation within the pre-impact bodies is considered. This result holds true irrespective of whether density-driven mantle overturn occurred in the pre-impact bodies. Instead, the observed similarity favors extensive post-impact homogenization of the proto-lunar disk, a process consistent with a high-energy giant-impact Moon formation scenario (e.g., Synestia).

¹Robin L. Haller, ¹Martin R. Lee
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.10.034]
¹School of Geographical and Earth Sciences, University of Glasgow, Glasgow G12 8QQ, UK
Published by arrangement with John Wiley & Sons

The most abundant group of carbonaceous chondrites are the Mighei-like (CM) meteorites, and they span petrologic types ranging from almost unaltered (CM3) to heavily aqueously processed (CM1). The factors that controlled the extent of aqueous alteration that CM chondrites experienced on their parent body/bodies are debated and remain poorly constrained. Geochemical models, and equilibrium models in particular, are powerful tools for emulating water–rock (W/R) interactions as a function of different parameters and conditions. In order to investigate possible CM chondrite alteration conditions and evaluate controlling factor(s) on petrologic type we modelled the interaction of a CM3 proxy, the CO3.0 chondrite Dominion Range 08006, with a fluid under different temperatures (1–150 °C), W/R ratios (by mass) (0.2–5) and solute concentrations (0.2–2 mol/kg CO2, 0.02–0.2 m NH3, 0.01–0.1 m H2S and 0.001–0.01 m HCl). Five additional scenarios that use the same parameter space but with differences in properties including pressure and redox conditions were also created to further investigate the controls on petrologic type. Systems that are CM chondrite-like from their close similarity to the mineralogy of CM meteorites as determined by sample analysis can form under a wide range of temperatures (1–140 °C), W/R ratios (by mass) (0.3 – 5), solute concentrations (0.2 – 2 m CO2), pH (8.5 – 12.6) and pe (−10.8 – −6.6). Across the different scenarios CM2-like systems are most abundant followed by CM1-like, whereas CM1/2-like systems are rare. Differences in petrologic type can be mainly attributed to variations in temperature, with CM1s overall being formed by alteration at higher temperatures (80–140 °C) than CM2s (1–105 °C). CM1/2 chondrites might be produced by elevated W/R ratios (by mass) and/or solute concentrations. From a mineralogical perspective, CM chondrites of different petrologic type might have originated from contrasting regions of a singular, thermally stratified parent body. Some differences between model results and CM chondrite samples could be addressed by more sophisticated tools like kinetic modelling.