International audienceThe Philae lander provides a unique opportunity to investigate the internal structure of a comet nucleus, providing information about its formation and evolution in the early solar system. We present Comet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT) measurements of the interior of Comet 67P/Churyumov-Gerasimenko. From the propagation time and form of the signals, the upper part of the “head” of 67P is fairly homogeneous on a spatial scale of tens of meters. CONSERT also reduced the size of the uncertainty of Philae’s final landing site down to approximately 21 by 34 square meters. The average permittivity is about 1.27, suggesting that this region has a volumetric dust/ice ratio of 0.4 to 2.6 and a porosity of 75 to 85%. The dust component may be comparable to that of carbonaceous chondrites

Analysis of the propagation of the Comet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT) signal throughout the small lobe of the 67P/CG nucleus has permitted us to deduce the real part of the permittivity, at a value of 1.27 ± 0.05. The first interpretation of this value, using the dielectric properties of mixtures of ices (H 2 O, CO 2 ), refractories (i.e. dust) and porosity, led to the conclusion that the comet porosity lies in the range 75-85 per cent. In addition, the dust-to-ice ratio was found to range between 0.4 and 2.6 and the permittivity of dust (including 30 per cent porosity) was determined to be lower than 2.9. This last value corresponds to a permittivity lower than 4 for a material without any porosity. This article is intended to refine the dust permittivity estimate by taking into account updated values of the nucleus densities and dust/ice ratio and to provide further insights into the nature of the constituents of comet 67P/CG. We adopted a systematic approach: determination of the dust permittivity as a function of the volume fraction of ice, dust and vacuum (i.e. porosity) and comparison with the permittivity of meteoritic, mineral and organic materials from literature and laboratory measurements. Then different composition models of the nuclei corresponding to cosmochemical end members of 67P/CG dust are tested. For each of these models, the location in the ice/dust/vacuum ternary diagram is calculated based on available dielectric measurements and confronted to the locus of 67P/CG. The number of compliant models is small and the cosmochemical implications of each of them is discussed, to conclude regarding a preferred model.

International audienceSoil Moisture and Ocean Salinity (SMOS), launched on 2 November 2009, is the first satellite mission addressing sea surface salinity (SSS) measurement from space. Its unique payload is the Microwave Imaging Radiometer using Aperture Synthesis (MIRAS), a new two-dimensional interferometer designed by the European Space Agency (ESA) and operating at the L-band frequency. This article presents a summary of SSS retrieval from SMOS observations and shows initial results obtained one year after launch. These results are encouraging, but also indicate that further improvements at various data processing levels are needed and hence are currently under investigation