Acoustic sounding as a new method for planetary surface research

Abstract

Future exploration missions like Rosetta, ExoMars and lunar missions will provide in-situ experiments for the investigation of planetary surface properties. The analysis of mechanical vibrations may provide a new means to study the structure and properties of the surface layers of terrestrial planets and minor bodies like comets. The Comet Acoustic Surface Sounding Experiment (CASSE) on the Rosetta Lander Philae will try to determine elastic parameters and the structure of the surface layer of the target comet. Surface layers critically determine the exchanges of volatiles, non-volatile materials and energy with the surrounding environment. Impacts, volcanism, erosion and the presence of an atmosphere influence the evolution of the surfaces. The analysis of mechanical vibrations caused by artificial acoustic sounding may provide a new means to study the properties and the structure of the surface layer of terrestrial planets and minor bodies like comets. Elastic surface parameters can be determined from the sound velocities of acoustic waves in the soil. The use of 3-axes accelerometers as receivers offers the possibility to study the polarisation of propagating elastic waves. This polarisation analysis allows separating the mixture of different propagating waves and the determination of the sound velocities. In addition, we will demonstrate how nearby acoustic or seismic sources can be localised. We will present the potential of acoustic sounding for the short range investigation of planetary surface layers.