Dielectric Modeling of Comet Nuclei and Asteroids: Implications for Rosetta and Dawn Radar Studies

Details Dielectric Modeling of Comet Nuclei and Asteroids: Implications for Rosetta and Dawn Radar Studies Dielectric Modeling of Comet Nuclei and Asteroids: Implications for Rosetta and Dawn Radar Studies

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p11e1620p&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #P11E-1620

Physics

[6205] Planetary Sciences: Solar System Objects / Asteroids, [6210] Planetary Sciences: Solar System Objects / Comets, [6964] Radio Science / Radio Wave Propagation, [6024] Planetary Sciences: Comets And Small Bodies / Interiors

Scientific paper

In 2014, the European Space Agency's Rosetta spacecraft is scheduled to rendezvous with Comet 67P/Churyumov-Gerasimenko, a primitive object that will provide insight into the history and origins of the Solar System. NASA's Dawn mission targets a much larger small body, having begun orbit of asteroid-belt member 4 Vesta in July of 2011. The implementation of a radar experiment would allow the study of surface and shallow subsurface structure in each case, while also of deep interior structure for Comet 67P. Once in orbit, Rosetta will enact the CONSERT experiment, which will propagate low frequency radar waves (90 MHz) through C67's nucleus between its lander and orbiter, and measure the signal's dispersive effects to form a tomographical reconstruction of the interior. Dawn may be able to conduct a related bistatic radar (BSR) experiment at higher frequency band (near 8 GHz) if it reflects the spacecraft's telemetry signal off Vesta near the Brewster angle, using the Earth as the receiving end. Different factors would contribute to the signal dispersion in each case, primarily including surface roughness and electromagnetic properties inherent within each body that vary with composition. In order to anticipate these radar experiments, multiple models of Comet 67P's and Vesta's geophysical compositions have been postulated. When coupled with laboratory measurements of temperature, porosity, and dust-to-ice ratio effects on dielectric values of materials analogous to a comet or asteroid, respectively, we have constructed three-dimensional visualizations of their theoretical dielectric compositions. Three-dimensional dielectric models of their outer surfaces illustrate the effects of temperature changes due to sunlight, which help quantify each object's outermost transparency to radio waves at 90 MHz and X-band radar frequencies respectively. Models of the hypothesized internal structure are coupled with radio-wave propagation simulations, and are used to further quantify the possible level of depth penetration, as well as assess ice enrichment. By considering multiple models of each nucleus's dielectric structure, we expect to constrain the radar measurement requirements that would be needed to explore subsurface ice occurrences on Vesta, and which will support data inversion for the CONSERT experiment on Comet 67P.

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