Mascons and Isostasy

Abstract

POSITIVE gravity anomalies have been measured over the circular maria on the Moon¹ and have been taken as evidence that the Moon is not in isostatic equilibrium and must have great strength to great depths. It is further argued that this implies a cold origin for the Moon². Muller and Sjogren¹ adjusted their measurements to give the gravitational field at a height of 100 km above the lunar surface by making reasonable assumptions about the field gradient. They applied no correction to take account of the topography of the surface and none to allow for isostasy. Their published map therefore shows “free air” anomalies. Here I show that the large, positive free air anomalies can be consistent with complete isostatic adjustment of the circular maria and, consequently, that the Moon may be warm at relatively shallow depths.