Can tidal tomography be used to unravel the long-wavelength structure of the lunar interior?

Abstract

The Moon displays a number of hemispherically asymmetric features that may be related to long-wavelength structure and dynamics in the lunar mantle. Here we propose to use observations of the non-degree-2 gravitational response of the Moon to degree-2 tidal forcing to constrain the long-wavelength lunar mantle structure. For a planetary body with laterally varying structure, degree-2 tidal forces excite gravitational response at non-degree-2 harmonics due to mode coupling effects. Using a new numerical model, we determine that for a lunar mantle with ∼5% hemispherical variations in seismic shear wave velocity V s, the degree-3 response could reach ∼2% of the degree-2 response. The larger the hemispherical variations in V s, the larger the degree-3 response. We suggest that if observations from recent lunar missions such as SELENA and GRAIL could be used to determine the non-degree-2 tidal response, it might be possible to place constraints on the lunar mantle structure. © 2012. American Geophysical Union. All Rights Reserved.