Characterization of lunar swirls at Mare Ingenii: A model for space weathering at magnetic anomalies

摘要

Analysis of spectra from the Clementine ultraviolet-visible and near-infrared cameras of small, immature craters and surface soils both on and adjacent to the lunar swirls at Mare Ingenii has yielded the following conclusions about space weathering at a magnetic anomaly. (1) Despite having spectral characteristics of immaturity, the lunar swirls are not freshly exposed surfaces. (2) The swirl surfaces are regions of retarded weathering, while immediately adjacent regions experience accelerated weathering. (3) Weathering in the off-swirl regions darkens and flattens the spectrum with little to no reddening, which suggests that the production of larger (>40 nm) nanophase iron dominates in these locations as a result of charged particle sorting by the magnetic field. Preliminary analysis of two other lunar swirl regions, Reiner Gamma and Mare Marginis, is consistent with our observations at Mare Ingenii. Our results indicate that sputtering/vapor deposition, implanted solar wind hydrogen, and agglutination share responsibility for creating the range in npFe~0 particle sizes responsible for the spectral effects of space weathering.