G33B-0955: Gravitational signatures of the Moon's near-surface features from GRAIL

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Authors: Michael Sori, Maria T Zuber

Author Institutions: Earth, Atmospheric and Planetary Sciences, M.I.T., Cambridge, MA, USA

Observations from the Gravity Recovery and Interior Laboratory (GRAIL) mission [Zuber et al., 2011] have provided the highest resolution and most accurate gravity data of the Moon to date. Combining these data with topographic data from the Lunar Orbiter Laser Altimeter (LOLA) [Smith et al., 2011] aboard the Lunar Reconnaissance Orbiter (LRO) [Chin et al., 2007] has allowed for construction of a global 16 pixels per degree map of lunar Bouguer anomalies. In this study, we analyze Bouguer gravity to study shallow subsurface structure. Analysis of data from the Clementine mission [Neumann et al., 1996] revealed that some lunar basins contain positive Bouguer anomalies that are in excess of that due to maria infill. This excess has been attributed to mechanisms that uplift high density mantle material closer to the surface, either during [e.g. Neumann et al., 1996] or after [e.g. Andrews-Hanna and Stewart, 2011] basin formation. GRAIL data allow for a more thorough analysis of these “mascons.”รน We search for correlations between a basin’s topographic expression and its gravitational signature, and find a strong correlation between basin diameter and the magnitude of the Bouguer anomaly found in the center of the basin. Positive gravity anomalies are present in basins as small as ~190 km in diameter, and exist for all basins greater than ~270 km in diameter. GRAIL data are also particularly apt for studying cryptomaria, i.e. mare basalt deposits that are hidden from the surface beneath a layer of higher albedo material. Previous authors [Antonenko et al., 1994] have provided criteria for the detection of cryptomaria, especially the presence of dark-halo craters [e.g., Schultz and Spudis, 1979]. We use the Bouguer anomaly map to study areas where cryptomaria deposits are thought to exist, such as the Schiller-Schickard region [Bell and Hawke, 1984].

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