^1,2A.P.Jordan,³A.W.Case,^1,2J.K.Wilson,¹C.-L.Huang
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115011]
¹Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH, USA
²Solar System Exploration Research Virtual Institute, NASA Ames Research Center, Moffett Field, CA, USA
³Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA
Copyright Elsevier

The standard view of space weathering on the Moon is that the solar wind and micrometeoroid impacts alter the optical properties of lunar soil. A third process—dielectric breakdown driven by solar energetic particles (SEPs)—has also been suggested to contribute to space weathering. It has been difficult to determine the relative roles of these processes. The Earth’s magnetotail, however, provides a way to distinguish between them, because it affects only charged particles. Earth’s magnetotail blocks the solar wind, and here we show that it also likely reduces the flux of SEPs traveling across the tail and impacting the tail-facing hemisphere of the Moon when it is entering or leaving. Consequently, we make two predictions that distinguish how the tail affects dielectric breakdown weathering patterns from how it affects solar wind weathering patterns. First, the magnetotail should create two minima in the total amount of breakdown weathering that has occurred: one near  and a deeper one near  longitude. Second, the tail should create east–west asymmetries in the breakdown weathering of crater walls, with the greatest asymmetries occuring at  longitude. Although the first prediction has proven difficult to test, we find that the second prediction is supported by observations. Therefore, we conclude that investigations of space weathering must consider, not only micrometeoroid and solar wind bombardment, but also dielectric breakdown.

¹William H.Farrand,²Christopher S. Edwards,²Christian Tai Udovicic
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115021]
¹Space Science Institute, 4765 Walnut Street, Suite B, Boulder, CO 80301, USA
²Department of Astronomy and Planetary Science, Northern Arizona University, Flagstaff, AZ 86011, USA
Copyright Elsevier

The Tacquet Formation (TF) was first identified in geologic mapping of southern Mare Serenitatis as a distinct low albedo region split by the linear Rimae Menelaus rilles. A distinct western dome, split by a linear rille and less distinct eastern dome (the Menelaus domes) are also present within the TF. Previous Earth-based radar analyses showed that the TF has a lower circular polarization ratio consistent with a pyroclastic mantle. In this study, compositional and spectroscopic parameters were derived from Moon Mineralogy Mapper (M3) data. Lunar Reconnaissance Orbiter Camera Wide Angle Camera (LROC WAC) and SELENE Kaguya Multiband Imager (MI) multispectral data were also utilized. FeO derived from MI data for the TF and Menelaus domes was elevated at levels consistent with pyroclastic glasses. While not diagnostic of pyroclastics, TiO2 derived from LROC WAC data over the TF and Menelaus domes was also elevated relative to the background materials. Analysis of 1 and 2 μm band parameters also show the TF and Menelaus domes as being distinct with a band center moderately longer than 1 μm and 2 μm band center shorter than the surroundings, characteristics consistent with pyroclastic glass and/or increased ilmenite. M3 data thermally corrected via two different thermal correction approaches indicate a moderately deeper band in the 3 μm region indicative of OH and/or H2O, a characteristic that is also potentially associated with pyroclastic deposits. These compositional findings are consistent with the Earth-based radar data suggesting that the TF is a pyroclastic mantle and potentially represents a previously unrecognized sub-class of pyroclastic deposits associated with lunar volcanic domes.