P31E-2115
Measuring the Permittivity of the Nucleus of a Comet: the PP-SESAME Experiment on Board the Philae/ROSETTA Lander

Wednesday, 16 December 2015
Poster Hall (Moscone South)
Anthony Lethuillier1, Alice Anne Le Gall1, Michel Hamelin2, Valerie Ciarletti1, Sylvain Caujolle-Bert1, Walter Schmidt3, Rejean Grard4, Klaus J. Seidensticker5 and Hans-Herbert Fischer6, (1)LATMOS Laboratoire Atmosphères, Milieux, Observations Spatiales, Paris Cedex 05, France, (2)UPMC (Univ. Paris) / LATMOS, Paris, France, (3)Finnish Meteorological Institute, Helsinki, Finland, (4)European Space Research and Technology Centre, Noordwijk, Netherlands, (5)Deutsches Zentrum für Luft- und Raumfahrt, Institut für Planetenforschung, Berlin, Germany, (6)German Aerospace Center DLR Cologne, MUSC, Cologne, Germany
Abstract:
The Permittivity Probe (SESAME-PP) on-board the Philae Lander of the ROSETTA mission was designed to constrain the complex permittivity of the first 2 m of the nucleus of comet 67P/Churyumov-Gerasimenko and to monitor its variations with time. Doing so, it is meant to provide a unique insight into the composition of the comet, and in particular, into its water content. PP-SESAME acquired data on November 13, 2015, both during Philae descent to the comet and at the surface of the nucleus.

The PP-SESAME instrument is derived from the quadrupole array technique. A sinusoidal electrical current is sent into the ground through a transmitting dipole, and the induced electrical voltage on a receiving dipole is measured. The complex permittivity of the material is inferred from the mutual impedance derived from the measurements. In practice, the influence of both the electronic circuit of the instrument and the conducting elements in its close environment must be accounted for in order to best estimate both the dielectric constant and electrical conductivity of the ground. For that purpose, we have developed a method called the “capacity-influence matrix method”.

A replica of the instrument was recently built in LATMOS (France) in order to validate this method. In this paper, we will present the tests conducted with the replica in a controlled environment and their comparison to numerical simulations. We will also show simulations relevant to the PP-SESAME experiment on the nucleus of comet 67P/Churyumov-Gerasimenko. These simulations were run for realistic scenarios of the Philae’s attitude and environment at its final landing site. We discuss their implications in terms of surface electrical and compositional properties.

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