A new study of crater concentric ridges on the Moon

Crater concentric ridges (CCRs) are topographic ridges found in the ejecta blankets of fresh few-kilometer-scale lunar craters. These ridges, which were last studied in detail in the late 1970 s (referred to as 'lunar concentric dunes'), were hypothesized to form due to ballistic impact sedimentation and erosion. We have surveyed the Moon to find 59 craters with CCRs and have constructed mosaics of these craters where possible using high-resolution LROC NAC (Lunar Reconnaissance Orbiter Camera-Narrow Angle Camera) images. We then map from some of these mosaics in order to measure the CCRs and examine their morphologies. Ejecta scaling models and some of our observations of the CCRs contradict the current hypothesis for the formation of these features. We therefore propose new hypotheses to consider for the formation of CCRs, specifically interaction of ejecta with initial topography or formation via interactions of shocks in the ejecta. Additionally, for the first time we have found CCRs on Mercury, but they are rare or absent on Mars.