Inferences on the lunar temperature from gravity, stress state and flow laws

Abstract

Inferences on the lunar temperature regime are made from the inversion of gravity for density anomalies and the stress-state of the Moon's interior, and by comparing these results with flow laws and estimates of likely strain-rates. The nature of the spectrum of the lunar gravitational potential indicates that the density anomalies giving rise to the potential are mainly of near-surface origon. The average stress-differences in the lunar mantle required to support these density anomalies are of the order of a few tens of bars and have persisted for more than 3 · 10 9 years. If current flow laws for dry olivine can be extrapolated to the conditions of the lunar mantle, and the selenotherms based on electrical conductivity models are valid, the strain rates are too high to explain the preservation of the lateral near-surface density anomalies. We suggest that the present temperatures in the Moon are relatively low, of the order of 800°C or less, at a depth of about 300 km. This compares with 1100°C based on electrical conductivity models and is near the lower limit predicted by Keihm and Langseth (1977) from lunar heat-flow observations.