Mass, Density and Composition of the Nucleus 67P/Churyumov-Gerasimenko

Cometary nuclei consist mostly of dust and water ice, but the internal structure of a comet nucleus is essentially unknown. Bulk properties such as mass, volume (size and shape), and particularly the density, must be known for constraining its internal structure. The radio science experiment RSI on the Rosetta spacecraft derived the mass and the gravity field of comet 67P/Churyumov-Gerasimenko at distances varying between 100 km and 10 km, and together with the current best estimates of the volume by the OSIRIS camera, the bulk density of the nucleus. A model of the internal structure is derived from the information of two shape models by comparing observed and theoretical gravity coefficients. The comet nucleus appears to be a body of low mass, low density and high porosity with approximately four times more dust than ice by mass and 1.5 times more dust than ice by volume.