Acoustic Sounding as a new Method for Planetary Surface Research

Abstract

: 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. The combination of ground penetrating instru¬ments like PLUTO (PLanetary Underground TOol), developed for the Mars Express lander Beagle 2, as strong acoustic sources with CASSE-like triaxial 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 than a surface placed instrument and could allow a 3D-tomography of the surface layer. The main goal of our DFG project is the develop-ment of measurement methods that use mechanical vibrations in the auditable frequency range to deter-mine various properties of surface layers. As acoustic sources we use penetration instruments used or fore-sean for space experiments. Fully developed methods should allow to determine e.g. elastic properties or the structure of near-surface layers. In this talk we will present our work on the identifi-cation of different wave types in the recordings of acoustic sounding through granular material. We will also show how near-surface layers can be detected from recorded refractograms. And finally we will demonstrate a method to track penetrating sounders like PLUTO. This method could also allow the loca-tion of seismic events in the neighborhood of a space instrument like CASSE.