Dielectric properties of comet analog refractory materials

Ground penetrating radio waves or radar provide a promising technique for the study of sub-surface planetary or cometary material. The comet nucleus sounding experiment by radiowave transmission (CONSERT) will be the only experiment on board the ROSETTA mission to provide information on the interior of the comet Wirtanen. Other projects planned or under development are Marsis/Mars Express and GPR for Net Lander. The aim is to perform a radar tomography, and the necessary data inversion of the measured permittivity requires knowledge of the complex dielectric permittivities of probable sub-surface materials, so laboratory studies of the dielectric properties of analog geological materials have become necessary. nection with the Rosetta mission, we have characterized the dielectric permittivity of dunite, montmorillonite and kaolinite. We used granular materials identical to those of the KOSI comet simulation experiment conducted at DLR in Cologne (1987–1992). These materials were chosen as analog materials for the refractory component of comets and the compositions and grain size distributions of the powders are known. The present measurements covered temperatures increasing from 77 to 360 K at frequencies 120 Hz, 1.2 and 12 kHz. The powders were tested as received (exposed to atmospheric humidity), dried and after water impregnation. We find that the dielectric properties are consistent with the hypotheses on which the CONSERT instrument was designed.