Earth‐Based 70 cm Radar Data Reveal Heterogeneous Orientale Ejecta in the Nearside Southern Lunar Highlands

Abstract Understanding the lunar highlands near‐surface structure is critical in untangling basin chronology and constraining crustal evolution, particularly for exploring the south polar region. We investigate the upper ∼30 m of the nearside southern highlands using Arecibo 70‐cm radar data and find a broad increase in backscatter of ∼3 dB (factor of two), as well as a paucity of radar‐bright craters in a topographic depression several hundred km in diameter. We also identify radar‐bright streaks within the region that have consistent alignment with Orientale ejecta. Based on these observations and modeled basin ejecta thickness, we interpret the radar‐bright region as Orientale ejecta at least several meters thick, which may have accumulated in a local topographic depression. We rule out a cryptomare origin for the radar‐bright region based on radar backscatter variations and lack of other supporting evidence. The radar‐bright region is likely enhanced in dm‐ to m‐scale boulders and/or has a lower dielectric loss tangent than surrounding regions, indicating a compositional variation relative to nearby highlands. Mineralogical variations driving possible loss tangent changes are unknown. Large basin ejecta lenses are likely to be present across the highlands and can be investigated by upcoming surface missions.