Dust Impact Monitor (SESAME-DIM) Measurements at Comet 67P/Churyumov-Gerasimenko

Abstract

The Philae lander carries the Dust Impact Monitor (DIM) on board, which is part of the Surface Electric Sounding and Acoustic Monitoring Experiment (SESAME). DIM employs piezoelectric PZT sensors to detect impacts by sub-millimeter and millimeter-sized ice and dust particles that are emitted from the nucleus and transported into the cometary coma. The sensor measures dynamical data like flux and the directionality of the impacting particles. Mass and speed of the grains can be constrained for assumed density and the elastic modulus of the grains. DIM was operated during Philae's descent to its nominal landing site Agilkia and detected one particle impact at an altitude of approximately 2.4 km from the nucleus surface. This is the closest ever dust detection at a cometary nucleus by a dedicated in-situ dust detector. Laboratory calibration experiments performed with compact and porous cometary analogue materials showed that the detected particle had a low bulk density of approximately 250 kg m ^-3, and a radius of about 1 mm. The measured parameters can be understood in the context of a simple gas flow model. At Philae's �nal landing site, Abydos, DIM detected no dust impact which may be due to low cometary activity in the vicinity of Philae, or due to shading by obstacles close to Philae, or both.