REVISITING RADAR ANOMALOUS CRATERS WITH SHADOWCAM IMAGE DATA

The lunar permanently shadowed regions (PSRs) interest the science and exploration communities due to their potential to cold-trap volatile species. However, while some evidence suggests the presence of volatile-rich deposits, such as from the LCROSS impact experiment, definitive evidence for water ice within PSRs remains elusive. Due to their perpetual darkness, observations of PSR terrains at visible wavelengths are challenging. ShadowCam, a NASA-contributed instrument onboard the Korea Pathfinder Lunar Orbiter (KPLO), is a sensitive camera designed to image within PSRs utilizing scattered light and is a crucial next step to characterizing PSR terrains.

Previous workers interpreted radar signatures of some PSR craters as “anomalous” in that they do not display the expected characteristics of crater deposits. Fresh craters typically show a high Circular Polarization Ratio (CPR), the ratio of same to opposite sense polarized radar signatures, inside and outside the crater. However, Spudis et al., 2010 observed that some craters within PSRs only display an elevated CPR signature inside the crater, which they interpreted as consistent with the presence of buried water ice deposits. However, recent work has suggested that this high CPR signature only inside the crater rim is not anomalous but represents a typical stage of crater evolution.

Initial analysis of ShadowCam image data shows high CPR regions in typical craters are correlated with multiple surface blocks. Some of the craters previously identified as anomalous show high CPR areas where no surface blocks are evident, possibly indicating either buried rocks, buried ice, or a change in dielectric properties. We will present these initial analyses to assess the correlation between elevated CPR signatures and the distributions of surface blocks within crater interiors. By doing so, we gain a holistic view of proposed radar anomalous crater characteristics to assess their potential for harboring volatiles and the implications of their presence.