Compressive strength and elastic modulus at Agilkia on comet 67P/Churyumov-Gerasimenko derived from the SESAME/CASSE touchdown signals

We report an analysis of the Comet Acoustic Surface Sounding Experiment (CASSE) acceleration signals at Philae's first touchdown site Agilkia on comet 67P/Churyumov-Gerasimenko. The signals yield the forces in the contact zone foot-sole and comet surface, and from these forces a compression strength of approximately 10 kPa can be derived. The sole's contact-resonances provide an elastic modulus of the order of 10 MPa. Our results are partially based on calibration experiments, which are described in the appendix of the current paper. Relations known in material science, linking porosity to elasticity and fracture energy, allow one to check the interdependence between compression strength and elasticity.