Lunar Cold Spots and Crater Production on the Moon. Issue 9 (19th September 2018)

• Record Type: Journal Article
• Authors: Williams, J.‐P.; Bandfield, J. L.; Paige, D. A.; Powell, T. M.; Greenhagen, B. T.; Taylor, S.; Hayne, P. O.; Speyerer, E. J.; Ghent, R. R.; Costello, E. S.
• Is Part Of: Journal of geophysical research. Volume 123:Issue 9(2018)
• Page Start: 2380
• Page End: 2392
• Publication Date: 2018-09-19
• Subjects: Moon -- diviner -- cold spots -- impact craters -- regolith; Planets -- Periodicals; Geophysics -- Periodicals; 559.9
• DOI: 10.1029/2018JE005652
• Languages: English
• ISSNs: 2169-9097

Abstract

Abstract: Mapping of lunar nighttime surface temperatures has revealed anomalously low nighttime temperatures around recently formed impact craters on the Moon. The thermophysically distinct "cold spots" provide a way of identifying the most recently formed impact craters. Over 2, 000 cold spot source craters were measured with diameters ranging from 43 m to 2.3 km. Comparison of the crater size‐frequency distribution with crater chronology models and crater counts of superposed craters on the ejecta of the largest cold spot craters constrains the retention time of the cold spots to no more than ~0.5–1.0 Myr with smaller cold spots possibly retained for only few hundred kyr. This would suggest a relatively rapid impact gardening rate with regolith overturn depths exceeding ~5 cm over this time scale. We observe a longitudinal heterogeneity in the cold spot distribution that reflects the Moon's synchronous rotation with a higher density of cold spots at the apex of motion. The magnitude of the asymmetry indicates the craters formed from a population of objects with low mean encounter velocities ~8.4 km/s. The larger cold spots ( D > 800 m) do not follow this trend, and are concentrated on the trailing farside. This could result from a shorter retention time for larger cold spots on the leading hemisphere due to the greater number of smaller, superposed impacts. Alternatively, the abundance of large cold spots on the trailing farside resulted from a swarm of 100‐m‐scale impactors striking the Moon within the last ~0.5 Myr. Plain Language Summary: Impact craters on the Moon modify the surfaces around them, resulting in patches of colder nighttime surface temperatures. These "cold spots" fade over time. Using the cold spots as markers to identify the most recent impacts that have occurred on the Moon, we measured the diameters of all the craters with cold spots. Comparing the population of these craters with the expected impact rate, we estimate that the cold spots fade over a few hundred thousand years. The cold spots are also concentrated on the western hemisphere due to the Moon's synchronous rotation where the western half of the Moon always faces toward the direction of motion of the Moon orbiting the Earth. This suggests that a relatively slow population of objects impacted the Moon in the last few hundred thousand years. The largest cold spots, however, are concentrated on the trailing hemisphere. This could result either from more small impacts on the leading hemisphere destroying larger cold spots and leaving a higher number of large cold spots on the trailing hemisphere, or a swarm of 100‐m‐sized objects colliding on the trailing side during this time period. Key Points: We measure diameters of craters associated with cold spots. Their size‐frequency distribution indicates cold spots survive a few hundred kyr The distribution of cold spots reflects the Moon's synchronous rotation with cold spots focused on the apex of motion The largest cold spots with source craters larger than 800 m are concentrated on the trailing side of the moon