Courtney Jean Rundhauga, Martin Schillera, Martin Bizzarroa, Zhengbin Denga,b, Hermann Dario Bermúdezc,d,e
Earth and Planetary Science Letters 669, 119592 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2025.119599]
aCentre for Star and Planet Formation, Globe Institute, University of Copenhagen, Øster Voldgade 5–7, 1350 Copenhagen K, Denmark
bDeep Space Exploration Laboratory/CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, China
cDepartment of Earth and Environmental Studies, Montclair State University, Montclair, NJ 07043, USA
dGrupo de Investigación Paleoexplorer, 1400-37 Trexlertown Rd, PA 18062, USA
eDepartamento de Geociencias, Universidad Nacional de Colombia, Bogotá 11001, Colombia
The Cretaceous-Paleogene boundary (KPB) represents a massive extinction event in Earth’s history, probably triggered by the Chicxulub asteroid impact ∼66 Ma. The event dispersed vast volumes of ejecta materials including exceptionally preserved impact spherules in the Gorgonilla Island KPB section. Previous work identified three populations of spherules at Gorgonilla: 1) ballistically transported molten spherules, 2) a mixture of molten and condensed spherules dispersed by the expansion of a high-temperature, turbulent cloud (the “pyrocloud”), and 3) tiny droplets condensed from the plume (the “fireball layer”). We determine the Mg, Fe, and Ca isotopic compositions of pristine spherules to better understand the evaporation and condensation thermodynamics within the pyrocloud. We detect enrichment in mass bias corrected µ48Ca and µ26Mg* isotope signatures from the terrestrial value corresponding to an impactor contribution of ∼17–25%, most likely from a CM or CO chondrite-like asteroid. The mass-dependent δ25Mg and δ56Fe compositions are generally light or unfractionated, suggesting incomplete recondensation as the pyrocloud cooled and expanded. Combined δ25Mg and δ56Fe signatures reveal decoupling of these isotope systems, likely due to differing condensation rates. Thus, we calculate a higher average condensation rate of Fe than Mg, reflecting the thermodynamic decoupling and more complete recondensation signatures of Fe in the pyrocloud vapor. While we uncover information about the evaporation and condensation thermodynamics in the pyrocloud, the exact formation mechanisms of the complete suite of spherules remain complex with some spherules potentially forming from multiple mechanisms, including recondensation and splash–melting.
Day: September 17, 2025
Delivery of carbonaceous materials to the Moon
Linxi Lia,b,d, et al. (>10)
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2025.116802]
aState Key Laboratory of Lithospheric and Environmental Coevolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Copyright Elsevier
Asteroidal impacts play an important role in creating new lithology, shaping the morphology, and transporting water to the inner Solar System planets. Massive impact records have been preserved on the Moon; however, exogenous impactors have not been adequately identified in lunar samples. Here we carried out petrological and geochemical investigations on the newly lunar samples returned by Chang’e-6 (6CE) to estimate the source of impactors to the Moon. One spinel-bearing troctolite-like clast was identified in the 6CE soils. This clast displays porphyritic texture and is mainly composed of olivine (32 %), plagioclase (31 %), and mesostasis (34 %) with minor troilite (2 %) and spinel (1 %), and rare Fesingle bondNi metal, in area%. The sample olivines have a forsterite variation range of 75–85 and a Fe/Mn atomic ratio of 55–80. The trace element concentrations of Co (113–223 μg.g−1), Ni (121–938 μg.g−1), Cr (1191–4832 μg.g−1), and P (827–1645 μg.g−1) in olivines are notable higher than the typical lunar samples. Furthermore, these olivines exhibit notable 16O depletion features (δ18O: +10.7 ‰ to +16.7 ‰ and δ17O: +5.9 ‰ to +9.5 ‰). The investigated clast has a bulk Ir content of 51 ng.g−1, significantly higher than local lunar materials. The unusual texture, mineral chemistry, trace element concentrations, and oxygen isotopic compositions suggest this clast was likely derived from an impact event created by a CI- or CY-like carbonaceous chondrite. Such chemical and isotopic features are correlated with textures, indicating that some olivine have relict cores originated from the impactor. Such an impact event could have produced a new lithology of spinel-bearing troctolite on the Moon. Meanwhile, the carbonaceous chondritic impactor would have delivered a great amount of water and volatiles to the Moon.
Regolith without age? High-resolution regolith depth measurements across lunar maria
Elizabeth F.M. Atang
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2025.116790]
University of Idaho, Department of Physics, 875 Perimeter Dr. MS 0903, Moscow, ID 83844-0903, USA
Copyright Elsevier
In this work, we test the established hypothesis that lunar regolith depth increases with time because the surface is continually exposed to meteorite bombardment. If this hypothesis is correct, younger surfaces should have thinner regolith than older surfaces. Because many of the regolith depth studies in the literature are for surfaces older than 3 Gy, in this paper, we study Mare regions with a wide range of ages between 1.33 Gy and 3.88 Gy. To measure regolith depths, we used the small crater morphology method based on the work by Oberbeck & Quaide. We found median regolith depths between 1.6 m to 4.0 m across our study sites. Importantly, we did not find any correlation between the thickness of the regolith and the age of the surface within the Mare units we studied. We conclude by discussing whether this result represents a true lack of correlation, which would imply an incomplete understanding of regolith formation.
Cosmochemistry Papers 