GRAIL Reveals Beneath the Lunar Maria

With gravity data acquired by the dual Gravity Recovery and Interior Laboratory (GRAIL) spacecraft, in conjunction with altimetry data from the Lunar Orbiter Laser Altimeter (LOLA) investigation on the Lunar Reconnaissance Orbiter, we investigate buried craters within the lunar nearside maria.  The contrast of low reflectance material of the lunar nearside maria against the high reflectance, anorthositic highlands’ crust can be observed from Earth with the naked eye and is arguably one of the most recognizable features of the Moon. Geologic evidence supports the hypothesis that the maria flooded the lunar nearside between 3.8-2.5 Gya, obscuring much of the original physiographic expression of the nearside lowlands, nearly 20% of the entire surface.

Image Credit: NASA

Image Credit: NASA

We use several approaches to visually identify quasi-circular mass anomalies (QCMAs) with minimal or no topographic expression in the free-air gravity and Bouguer anomaly. We identify these anomalies through a systematic search of the lunar nearside in the free-air gravity and Bouguer anomaly maps with shifted and stretched color-scale ranges.  Using these methods, we identify quasi-circular mass anomalies, likely to be ancient impact events, buried by the lunar maria.  We use this crater population in conjunction with partially buried craters to investigate the age, average thickness, volume, and density of maria that have been emplaced on the lunar nearside.

Collaborators:  Jeffrey C. Andrews-Hanna, Jason M. Soderblom, Sean C. SolomonMaria T. Zuber

Acknowledgements:  This work was conducted as part of the GRAIL mission and is performed under contract to the Massachusetts Institute of Technology and the Jet Propulsion Laboratory, California Institute of Technology.  Thanks to  T.L. Grove, and J.T. Perron for their assistance and comments.

Affiliation:  This work was completed while A. J. Evans was affiliated with the Massachusetts Institute of Technology (MIT), Lamont-Doherty Earth Observatory at the Columbia University, and the Southwest Research Institute.