Global Distribution and Volume of Cryptomare and Visible Mare on the Moon From Gravity and Dark Halo Craters

Abstract

AbstractThe present‐day distribution of mare basalts on the Moon is an important constraint on the timing, duration, and flux of volcanism on the Moon. In this work, we find the global distribution of visible mares and cryptomares using the effective density (ρeff) of the Moon, which is sensitive to the vertical density distribution of the crust. We compute ρeff using the Gravity Recovery and Interior Laboratory (GRAIL) data and the Lunar Orbiter Laser Altimeter (LOLA) topography data. We apply this ρeff approach to the search of cryptomare for the first time, and we use a higher resolution grid and larger search area to constrain visible mare thicknesses compared to previous work. We use a Bayesian approach to find the distribution of mare thicknesses and density gradients of the underlying crust that is consistent with the localized ρeff. Assuming a bulk density of the mare basalts of 3,460 kg/m3, we find a mean visible mare thickness of km which is consistent with previous work. We find a candidate cryptomare volume of km3 representing more than half of the total mare volume on Moon. This volume is consistent with the higher end of the previously proposed values. Finally, we search for dark halo craters (DHC) globally to obtain geologic evidence of cryptomares and find 258 craters. Our results are consistent with extensive ancient volcanism, which explains the previously identified discrepancy between the early high volcanic flux predicted by thermal models of the Moon and the dearth of ancient volcanic deposits currently exposed.