On the composition of ices incorporated in Ceres

Abstract

We use the clathrate hydrate trapping theory (Lunine & Stevenson 1985) and the gas drag formalism of Weidenschilling (1977) to calculate the composition of ices incorporated in the interior of Ceres. In the spirit of the work of Cyr et al. (1998), and using a time dependent solar nebula model, we show that icy solids can drift from beyond 5 AU to the present location of the asteroid and be preserved from vaporization. We argue that volatiles were trapped in the outer solar nebula under the forms of clathrate hydrates, hydrates and pure condensates prior to having been incorporated in icy solids and subsequently in Ceres. Under the assumption that most of volatiles were not vaporized during the accretion phase and the thermal evolution of Ceres, we determine the per mass abundances with respect to H2O of CO2, CO, CH4, N2, NH3, Ar, Xe, and Kr in the interior of the asteroid. The Dawn space mission, scheduled to explore Ceres in August 2014 (Russel et al. 2004), may have the capacity to test some predictions. We also show that an in situ measurement of the D/H ratio in H2O in Ceres could constrain the distance range in the solar nebula where its icy planetesimals were produced.