¹Bailiang Liu,^1,2,3Jingnan Guo,¹Mikhail I. Dobynde,⁴Jia Liu,^1,2Yingnan Zhang,^1,2Liping Qin
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2023JE008069]
¹Deep Space Exploration Laboratory/School of Earth and Space Sciences, University of Science and Technology of China, Hefei, PR China
²CAS Center for Excellence in Comparative Planetology, USTC, Hefei, PR China
³Collaborative Innovation Center of Astronautical Science and Technology, Harbin, China
⁴Deep Space Exploration Laboratory, Institute of Deep Space Science, Hefei, China
Published by arrangement with John Wiley & Sons

The nucleosynthetic Cr isotope anomalies provides useful information to trace the source and origin of extraterrestrial samples, but it is usually influenced by high-energy cosmic rays, and evaluating such effect of cosmic rays in lunar samples is especially important. Those cosmic radiation particles (primary particles) can react with lunar materials, creating many secondary particles. Both primary and secondary particles can produce cosmogenic nuclides on the Moon. Radiation Environment and Dose at the Moon (REDMoon) is a novel GEANT4 Monte-Carlo model built to simulate the interactions of space particles with the lunar surface and subsurface content. Using this model, we simulate the production of cosmogenic Cr isotopes (50Cr, 52Cr, 53Cr, 54Cr) at different depths of lunar surface, and compare the contribution of different reactions generating these nuclides. The results suggest that spallation reactions are the most important process producing cosmogenic Cr isotopes. We also analyze the relationship between 53Cr/52Cr and 54Cr/52Cr predicted by our model and compare it with different Apollo samples. As previously studied, we also find an approximate linear relationship between ɛ53Cr and ɛ54Cr, where ɛ53Cr (or ɛ54Cr) is the relative deviation from the standard 53Cr/52Cr ratio (or 54Cr/52Cr ratio), normalized to 1/10,000. Furthermore, we reveal a change of this linear relationship in different depths of lunar surface. Besides, we investigate how the slopes can be influenced by exposure age and the Fe/Cr ratio. With these additional factors carefully considered, the comparison between our modeled results and the measurements is better than previous studies.

¹Matthew Varnam,¹Christopher W. Hamilton,^2,3Igor Aleinov,¹Jessica J. Barnes
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2024.116009]
¹Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd., Tucson, AZ 85716, USA
²Center for Climate Systems Research, Columbia University, New York, NY, USA
³NASA Goddard Institute for Space Studies, New York, NY, USA
Copyright Elsevier

Lunar volcanic volatiles are crucial for understanding eruption dynamics on the Moon as well as the potential formation, life span, and dissipation of a lunar secondary atmosphere. We review literature concerning volatile content, degassing extent, and speciation during the mare eruption period on the Moon from 4.0 to 1.2 Ga, providing a realistic summary of degassed compositions for the traditional volcanic elements C-O-H-S-F-Cl. The most reliable estimates of lunar volcanic volatiles come from high‑titanium (high-Ti) glass beads sampled during the Apollo 17 mission. Analysis of these samples demonstrates that hydrogen is the most abundant element by mole in erupted volcanic gases, so a hydrogen species should be the most abundant molecule in the lunar gas, rather than carbon monoxide. This hydrogen is expected to speciate mostly as H2, rather than H2O, at the predicted oxygen fugacity for lunar magma. This difference is important because H2 more easily escapes from the Moon, whereas H2O could freeze out on the lunar surface, and potentially persist within permanently shadowed regions near the poles. We also find that sulfur, rather than carbon, is the third most abundant element in lunar volcanic gas, after hydrogen and oxygen.