Comprehensive mass modeling of the Moon from spectrally correlated free‐air and terrain gravity data

Abstract

A lunar crust‐to‐core mass model for the region ±64° latitude was developed using gravity components evaluated from available spherical harmonic gravity and topographic field models that include Lunar Prospector, Clementine, and earlier satellite observations. Terrain gravity effects were computed at 100‐km altitude in spherical coordinates from 1° topography (GLTM 2) by Gauss‐Legendre quadrature integration. Corresponding free‐air gravity anomalies (LP75G) were spectrally correlated with the terrain effects to differentiate the terrain‐correlated and terrain‐decorrelated free‐air components. The absence of correlation between these free‐air components was interpreted for a Moho that may involve over 120 km of relief, assuming the lunar crust was mainly compensated by its thickness variations. Lacking the strong regional gravity effects of the terrain, the terrain‐decorrelated anomalies may be interpreted for their subcrustal components on the basis of their correlation spectrum with the free‐air anomalies. Inversions of the subcrustal anomalies inferred boundary undulations for the core‐mantle, asthenosphere‐lithosphere, and middle‐upper mantle that are remarkably correlated with surface impacts. The elevated core topography revealed beneath the Procellarum basin is consistent with the uplifting effects of the Imbrium impact and the development of the great lunar hotspot. Topographic undulations inferred for the lower and middle mantle reflect the dichotomized thermal evolution of the lunar near and far sides during bombardment time. On the nearside the results support the development of relatively thinner and hotter lithosphere by mantle convection that facilitated the diapiric rise of magma and mare flooding of the basins. For the farside the results favor the development of thicker and cooler lithosphere by viscous entrainment of lower density material into the lower mantle that limited basin flooding.