Discovery of a Lunar Cold Spot at Apollo 16's South Ray Crater

Abstract Lunar cold spots are extensive, ray‐like regions of reduced nighttime temperature surrounding young impact craters. Using improved Diviner temperature maps, we identify a faint cold spot surrounding South Ray crater at the Apollo 16 landing site. South Ray crater's age (2.08 ± 0.17 Ma) is consistent with the fading trend of other large cold spots, making it the oldest known cold spot. Astronaut footprint depths collected during the Apollo missions indicate a statistically lower relative density within the upper 15 cm of regolith at Apollo 16 compared to other Apollo sites. This agrees with thermal modeling, which requires a lower average density to explain the reduced nighttime temperatures. These results provide both in situ and orbital evidence that cold spots result from a decompaction of the upper centimeters of regolith. Further analysis of Apollo 16 samples and observations can inform our understanding of cold spot formation, and their influence on regolith evolution globally.