129-22 Boulders and Boulder Tracks in Permanently Shadowed Regions of the Lunar South Pole

Abstract:

This project maps boulders across the Lunar South Pole (LSP) using complementary datasets from the Lunar Reconnaissance Orbiter Narrow Angle Camera (NAC) and Korea Pathfinder Lunar Orbiter ShadowCam (SHC). While NAC imagery provides excellent coverage of illuminated terrain, permanently shadowed regions (PSRs) cannot be adequately observed. ShadowCam imagery supports boulder mapping in these previously inaccessible regions, allowing for a complete boulder inventory across the LSP. Because PSRs receive little to no direct solar radiation, weathering processes are expected to differ from those operating in illuminated terrain.

Using ArcGIS Pro, individual boulders were digitized as point features and boulder tracks as line features at a mapping scale of 1:1,500 to 1:3,000 across the LSP. Using the NAC dataset, 90,060 boulders and 782 boulder fields were identified across 9,878.51 square km. Nine regions of significant shadow were identified and mapped using ShadowCam. These regions cover 2,166 square km, with the largest region encompassing the combined area of Henson and Sverdrup craters at approximately 1,061 square km.

Preliminary mapping in shadowed regions identified 12,223 boulders across 2,166 square km of terrain. Boulder distribution varied considerably among the mapped regions, with densities ranging from 0.03 boulders per square km in areas where boulders were sparse to 39.44 boulders per square km where they were closely spaced. In addition, 29 significant boulders were identified, averaging 32 meters in length, with the largest measuring approximately 71 meters. Boulder tracks were concentrated primarily within Shackleton, with Sverdrup representing the only other mapped region containing tracks despite its much gentler slopes (<5°) compared to Shackleton (~30°). Future work will focus on using this expanded boulder dataset to compare illuminated and shadowed terrains and evaluating how temperature fluctuations and illumination influence the abundance, size, and preservation of lunar boulders.

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