Elastic Thickness of the Moon Estimated from the Global Admittance of Gravity and Topography

Abstract

Here we compare the free-air gravity anomaly model by the GRAIL (Gravity Recovery and Interior Laboratory) mission and the topographic model from the LRO (Lunar Reconnaissance Orbiter) laser altimetry. They showed a high correlation up to degree/order ～400. The gravity-topography admittance showed typical behaviors, i.e. it is low for degree/order below 50 (i.e. wavelengths longer than ～220 km), increased sharply, and kept constant at ～110 mgal/km. Such a wavelength dependence provides the information on the thickness of the surface elastic layer floating on ductile lower layer. We estimated the elastic thick-ness of the Moon to be ～14 km. This thickness is not significantly different from those found in the present Earth in spite of the smaller dimension of the Moon. This may suggest that the significant portion of the topographic features on the Moon was formed in the early ages of the Moon, when the heat flow was comparable to the present Earth.