Complete CASSE acceleration data measured upon landing of Philae on comet 67P at Agilkia

Abstract

On November 12th, 2014, the Rosetta lander Philae touched down at the site Agilkia on comet 67P. Here, we report unpublished data of the Comet Acoustic Surface Sounding Experiment (CASSE) which belonged to the Surface Electric Sounding and Acoustic Monitoring Experiment (SESAME). The CASSE signals were measured by the accelerometers built-in in the landing feet of Philae. Whereas the acceleration data in the direction perpendicular to the comet surface have been published earlier, the acceleration data measured parallel to the comet surface have been archived until now only on a server of the ESA Planetary Science Archive, and were not further evaluated. However, analyzing the acceleration data with the short-time Fourier-transform allows one to discern the time-sequence of the touch-down of the lander feet at the site Agilkia corroborating an earlier study by another group based on finite element calculations. In our analysis, the contact-resonances of the foot soles are exploited as a sign for surface contact. Because the acceleration data represent structure-borne sound in the foot soles in the audio range, they can be made audible in audio files which are attached to this publication.