Investigation of Planetary Surfaces with Acoustic Sounding

Abstract

The analysis of mechanical vibrations may provide a new means to study the structure and properties of the surface layer of terrestrial planets and minor bodies like comets. Seismic sounding proved quite effective not only on Earth but also on the Moon (Apollo missions). 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. The combination of ground penetrating instru¬ments as sounders like PLUTO (PLanetary Underground TOol), developed at the DLR for the Mars Express lander Beagle 2, or MUPUS, a heat probe instrument also on Philae, as strong acoustic sources with CASSE-like receivers offers large advantages in increased signal strength, variation of acoustic pathways and effective use of resources. This combination might easier overcome the attenuation problem in dry Regolith and allow a 3D-tomography of the surface layer. From the analysis of the polarisation of the recorded acoustic signals it is possible to separate the mixture of different propagating waves. These divers waves can be used for the determination of mechanical soil properties and near-surface layering. In addition we presented the possibility of the localisation of acoustic or nearby seismic sources out of the travel time or the polarisation of the acoustic waves.