¹Eunjin Cho (>10)
Journal of Geophysical Research: Planets, 131, e2026JE009905
Open Access Link to Article [DOI: 10.1029/2026JE009905]
¹Korea Astronomy and Space Science Institute, Daejeon, Republic of Korea

Published by arrangement with John Wiley & Sons

The lunar surface is heterogeneous in grain size and metallic iron abundance due to diverse histories of space weathering. The spectral and polarimetric properties of the lunar regolith are strongly affected by both grain size and metallic iron particles. However, because physical and chemical alteration processes are closely coupled in their effects on optical properties, their combined influence remains poorly constrained. In this study, lunar simulants (JSC-1A and KLS-1) were sieved into two bulk-type and three size-separated fractions, and hydrogen reduction was conducted to produce metallic iron particles on grain surfaces. The spectral and polarimetric properties of these samples were then systematically measured. After reduction, reflectance decreases while the degree of positive polarization increases, consistent with Umov’s law. In addition, reflectance contrasts among grain sizes are reduced because fine grains preferentially darken, whereas the polarization–albedo relation remains sensitive to grain size. The reflectance of bulk-type fractions is intermediate, unlike that of natural bulk lunar soils, which resembles the finest fractions. In contrast, the polarization–albedo behavior of bulk-type fractions is close to that of the finest fraction. These differences from natural lunar soils suggest that agglutinates, which are absent in our reduced samples, may be important for the optical properties of natural bulk lunar soils. Further comparisons using natural lunar soils will help clarify the relative roles of agglutinates and grain-surface weathering products in controlling the optical properties of lunar regolith.

¹Fabrice Gaillard, ²Luiz Pereira, ¹Laurent Arbaret, ¹Giada Iacono-Marziano, ¹Emmanuel Le Trong, ^1,3Fabien Bernadou, ⁴Yves Marrocchi
Science, 394, 97–101 Link to Article [DOI: 10.1126/science.aef2542]
¹Institut des Sciences de la Terre d’Orléans, CNRS/Université d’Orléans/BRGM, Orléans, France
²GEOLAB, Hangzhou International Innovation Institute, Beihang University, Hangzhou, China
³CNRS, Géosciences Environnement Toulouse (GET), Observatoire Midi-Pyrénées, Toulouse, France
⁴Université de Lorraine, CNRS, CRPG, Nancy, France

Peprinted with permission from AAAS

Atmophile elements (carbon, hydrogen, and nitrogen) were thought to accrete late during planetary formation, yet cosmochemical and astrophysical evidence suggests that they were already present while small bodies, such as Vesta, were forming. High-temperature magmatic events on small bodies, however, should have outgassed these ultravolatile elements because gravity would have been insufficient to retain them. In this study, experiments reveal that gas bubbles strongly attach to metal droplets in magma ocean–like mixtures, forming compounds that resist segregation. Early flotation of such compounds would have enhanced mantle siderophile endowment, eliminating the need for late accretion. On small bodies, low gravity would have enabled millimeter- to centimeter-sized compounds to sink, trapping atmophiles in their interiors. This mechanism links core formation to the early entrapment of atmophile elements and provides a framework for reconciling volatile delivery across planetary bodies and planetary accretion models.