Buried Impact Features on Mercury as Revealed by Gravity Data

Abstract

AbstractGravity data provide information about the internal mass distribution of celestial bodies. The latest gravity field model of Mercury, HgM007, has a higher spatial resolution than previously published gravity models, allowing smaller crustal structures to be resolved. In this study, a global free‐air gravity anomaly grid of Mercury was derived from the HgM007 gravity model using the spherical expansion method, and a Bouguer anomaly map was calculated based on the free‐air gravity and topography data. We used this gravity model to search for quasi‐circular Bouguer anomalies (QCBAs) larger than ∼109 km in diameter within the Northern Smooth Plains (NSP) of Mercury, where the resolution of the gravity data is the highest. Assuming that these QCBAs were correlated with mantle uplifts caused by ancient buried impact structures, we applied the prism rectangular shape model and the Markov chain Monte Carlo inversion method to determine the subsurface structure of these QCBAs. Four ancient buried basins, not clearly visible in the surface topography, were detected. We estimated the crustal thickness ratios and original rim‐to‐rim diameters for these four impact basins, based on empirical cratering scaling laws, finding that the thickness of the infill lava within the NSP might be 5 times larger than previously believed and the ancient terrain beneath the NSP might be older than previously thought.