• Statz, C.
• Plettemeier, D.
• Herique, A.
• Kofman, W. W.

Abstract

The Comet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT) aboard spacecraft Rosetta will perform a radar tomography of comet 67P/Chuyurmov-Gerasimenko's nucleus to provide a unique insight to its bulk geophysical properties based on the reconstructed complex permittivity distribution. This will be achieved by performing a bi-static sounding of the comet's core between the lander on the comet's surface and the orbiter. The data acquired through a discrete number of orbits during the first science phase will allow the construction of three-dimensional dielectric and structural models that will be used to constrain the ambiguities in current geophysical hypotheses on the cometary composition. A key factor for the successful reconstruction of the comet's inner properties is an accurate knowledge of the electromagnetic scattering and attenuation properties induced by the comet's shape, surface geomorphology, subsurface heterogeneities, bulk composition and temperature distribution in such complex environment that has yet to be characterized. In order to address these deficiencies, we perform time-domain simulations of two cometary dielectric models derived from different geophysical hypotheses of the layered-pile model by Belton et al. (2007): The dust-fraction model assumes an exponential variation of the dust to ice fraction from the surface toward the inner part of the nucleus with a fixed porosity of ~55%. For the porosity-dependent model an exponential variation of the porosity from the surface toward the inner part of the nucleus is assumed with a fixed dust-to-ice ratio of ~50%. Both models are detailed in Heggy et al. (2012) and implemented based on the Lamy shape model of 67P. The simulations were performed using the pseudo-spectral time-domain method which is suitable for large-scale electromagnetic scattering problems due to lower constraints on the discretization and higher accuracy compared to finite-difference schemes and yield a good estimation of the expected return signal properties at the receivers, both on the lander and the orbiter. In addition to the estimation of the attenuation function for each model, the received radar signatures will be used to evaluate the detectability of different subsurface structures. Our initial results suggest that the two provided models yield measurable different radar signatures with differences in the attenuation function and arrival times of the first wavefront due to the differences in the dielectric models. These results indicate that CONSERT will be capable of resolving different geophysical hypotheses on the comet....

Topics

• impedance spectroscopy
• surface
• phase
• experiment
• simulation
• tomography
• layered
• porosity