An estimate of the D/H ratio in Jupiter and Saturn's regular icy satellites – Implications for the Titan Huygens mission

Abstract

The solar nebula model described by Dubrulle (1993) and Drouart et al. (1999) is used to predict the D/H ratio in H2O ice of both Jovian and Saturnian regular satellite systems. These calculations take into account recent scenarios of formation of Jupiter and Saturn's large regular icy satellites developed from evolutionary turbulent models of the surrounding subnebulae. These scenarios argue that the Saturnian and Jovian subdisks were cold enough to prevent the vaporization of volatile species trapped in solids which produced the regular icy satellites. The hydrated solids formed in the feeding zones of Jupiter and Saturn during the cooling of the solar nebula. Hence, the D/H ratio in H2O ice of hydrated solids is likely the result of the isotopic exchange between HD and HDO which occurred in the solar nebula prior to the condensation of water. In these conditions, the D/H ratio in the regular icy satellites of Jupiter and Saturn is estimated to be between 3.8 and 4.7, and between 4.8 and 6.8 times the protosolar value, respectively. Such estimates, compared with subsequent in situ measurements of the D/H ratio in H2 Oi ce of the Jovian and Saturnian regular satellite systems, should bring new constraints on the proposed scenarios of formation. This is the case with the Huygens probe mission which has the capacity of measuring the D/H ratio in the water ice which may exist on the surface of Titan.