Cosmochemical implications of CONSERT permittivity characterization of 67P/C-G

Abstract : Unique information about the internal structure of the nucleus of comet 67P/C-G was provided by the CONSERT bistatic radar on-board Rosetta and Philae [1]. Analysis of the propagation of its signal throughout the small lobe indicated that the real part of the permittivity at 90 MHz is of (1.27±0.05). The first interpretation of this value using dielectric properties of mixtures of dust and ices (H2O, CO2), led to the conclusion that the comet porosity ranges between 75–85%. In addition, the dust/ice ratio was found to range between 0.4-2.6 and the permittivity of dust (including 30% of porosity) was determined to be lower than 2.9.The dust permittivity estimate is now reduced by taking into account the updated values of nucleus density and of dust/ice ratio, in order of providing further insights into the nature of the constituents of comet 67P/C-G [2]. We adopt a systematic approach: i) determination of the dust permittivity as a function of the ice (I) to dust (D) and vacuum (V) volume fraction; ii) comparison with the permittivity of meteoritic, mineral and organic materials from literature and laboratory measurements; iii) test of several composition models of the nucleus, corresponding to cosmochemical end members of 67P/C-G. For each of these models the location in the ternary I/D/V diagram is calculated based on available dielectric measurements, and confronted to the locus of 67P/C-G. The number of compliant models is small and the cosmochemical implications of each are discussed [2]. An important fraction of carbonaceous material is required in the dust in order to match CONSERT permittivity observations, establishing that comets represent a massive carbon reservoir.Support from Centre National d'Études Spatiales (CNES, France) for this work, based on observations with CONSERT on board Rosetta, is acknowledged. The CONSERT instrument was designed, built and operated by IPAG, LATMOS and MPS and was financially supported by CNES, CNRS, UJF/UGA, DLR and MPS. Rosetta is an ESA mission with contributions from its member states and NASA.[1] Kofman et al., Science, 349, 6247, aaa0639, 2015. [2] Herique et al., MNRAS, submitted, 2016.
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Submitted on : Friday, October 21, 2016 - 5:59:04 PM
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Anny Chantal Levasseur-Regourd, Alain Hérique, Wlodek Kofman, Pierre Beck, Lydie Bonal, et al.. Cosmochemical implications of CONSERT permittivity characterization of 67P/C-G. DPS 48 / EPSC 11 (Division for Planetary Sciences and the European Planetary Science Congress), Oct 2016, Pasadena, United States. ⟨insu-01385667⟩

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