Mechanical Properties of Comet 67P/Churyumov-Gerasimenko Measured by CASSE and DIM on Board Rosetta's Lander Philae

Kurzfassung

Background, Motivation, and Objective: In August 2014, the ESA spacecraft Rosetta encountered comet 67P. Rosetta carried the lander Philae that landed on the comet’s nucleus on November 12 2014. Philae housed ten different instruments including the Surface Electric Sounding and Acoustic Monitoring Experiment (SESAME), comprising CASSE. The objective of the Rosetta mission was to determine the properties of comet 67P. The mission ended on September 30 2016 with the deorbiting of Rosetta onto comet 67P. Statement of Contribution/Methods: The Comet Acoustic Surface Sounding Experiment (CASSE) is housed in the six soles of Philae’s landing feet. It consists of three piezoelectric tri-axial accelerometers, and three transducers. This allowed for both passive listening to the comet’s seismic activity and active sounding of the comet surface. Deceleration signals occurring in the first ms of the touchdown at the first landing site at an impact velocity of approx. 1 m/s were recorded. They contained information on Young's modulus E and on the crushing strength σ of the comet soil. A first analysis based on an inversion scheme exploiting Hertzian contact mechanics together with laboratory calibration tests was presented at the IEEE-IUS in 2015 (abstract 5 D-2), followed by a recent detailed account of the CASSE results /1/. The MUPUS listening experiment was a joint operation of two instruments on Philae: The Multi- purpose Sensors for Surface and Sub-Surface Science (MUPUS), and CASSE. While the main goal of MUPUS was to measure the thermal conductivity and the heat flow of the surface comet material by driving an instrumented rod into the ground /2/, a joint operation was carried out at the final landing site Abydos, since MUPUS used a hammering mechanism with stroke energies up to 4 Joules, constituting a strong source for surface waves in the 100 Hz to 2 kHz range /3/.