^1,2Alan E. Rubin
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14367]
¹Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California, USA
²Maine Mineral & Gem Museum, Bethel, Maine, USA
Published by arrangement with John Wiley & Sons

Meteorite collection inventories show that many related meteorite groups have very different numerical abundances (e.g., lunar versus Martian meteorites; Eagle Station pallasites versus main-group pallasites; eucrites versus diogenites; ungrouped Antarctic irons versus ungrouped non-Antarctic irons; carbonaceous chondrite-related (CC) iron meteorites versus noncarbonaceous chondrite-related (NC) iron meteorites). The number of members of individual meteorite groups reflects the entire history of these rocks from excavation on their parent bodies to recovery on Earth. These numbers are functions of six main selection factors: (1) volume of the parent-body source region, (2) depth of this source region, (3) time spent in interplanetary space, (4) friability of meteoroids in space and during transit through the Earth’s atmosphere, (5) susceptibility of meteorite finds to terrestrial weathering, and (6) post-fall biases resulting from geography, demography, and preferences by meteorite collectors and analysts. The numerical ratio of lunar/Martian meteorites (~1.8) results from several factors including the Moon’s proximity, the short transit time of lunar meteoroids through interplanetary space, the lower crustal depth from which lunar meteorites were excavated, the lower energy required to launch samples off the Moon than off Mars, and the lower porosity and higher mechanical strength of lunar meteorites. The dunite shortage among asteroidal meteorites may have resulted from the deeply buried olivine-rich meteoroids being ejected hundreds of millions of years ago at the same time as pallasites and irons; however, the dunitic meteoroids (with their lower mechanical strength) would have eroded in interplanetary space on much shorter time scales than their metal-rich fellow travelers.

¹Emily L. Fischer, ¹Stephen W. Parman
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2025.116664]
¹Department of Earth, Environmental, and Planetary Sciences, Brown University, 324 Brook St, Providence, RI 02912, United States of America
Copyright Elsevier

Enstatite chondrites are often used as models for the bulk composition of Mercury because they have similarly low oxygen fugacities. However, e-chondrites are too Si-rich to explain the observed composition of Mercury’s lavas. Here we explore a model in which an initially enstatite chondrite-like Mercurian silicate magma ocean loses Si to the large Fe core during early differentiation. We define a Mercury Fractionation Line (MFL) based on average basaltic geochemical terrane compositions and assume Mercury’s bulk silicate composition must fall along this line. We estimate that 26.5–36.7 ± 7.5 % (1σ) Si must be lost from an initial mantle to bring the e-chondrite compositions up to the MFL. Assuming that the Si is partitioned into the core, this implies a core Si content of 2.8–3.9 ± 0.8 wt% and an oxygen fugacity of IW–4.5 ± 1.0. We also show that a model where Mercury was initially ~2 times larger is consistent with more reducing oxygen fugacities (IW–5.0 ± 1.0) and a higher core Si content (~15 wt%). This estimated initial Mercury size is also consistent with predictions from dynamical simulations. We consider how Si partitioning into the core affects the δ30Si composition of the mantle. Though uncertainties are large, we show that as the initial radius of Mercury increases, δ30Si decreases, trending towards the δ30Si composition of enstatite chondrites. Our calculations do not constrain the mechanism by which Mercury’s mantle may have been lost. However, if they are correct, they imply that the mantle loss must have happened after core formation.