| Description |
Having retained and preserved pristine material from the Solar Nebula at the moment of their accretion, comets contain unique clues to the history and evolution of the Solar System. mportant diagnostics of how and where cometary materials formed are contained in isotopic ratios, since isotopic fractionation is very sensitive to chemical and physical conditions. Following the discovery of an Ocean-like D/Hratio in the water of the Jupiter-family comet 103P/Hartley 2 using HIFI (Hartogh et al. 2011, Nature, in press), we propose to obtain a high-accuracy D/H measurement in a long-period comet from the Oort cloud. Since measurements in Jupiter-family comets have only been acquired with Herschel, it is important to get a set of measurements for Oort cloud comets with the same instrumentation. Confirming the observed dichotomy in D/H ratio for long-period versus Jupiter-family comet would be the first clear compositional difference between these two dynamical classes of comets. The values and statistics of distribution of the D/H ratio in the two classes will improve our understanding of their origin in the Solar System, with implications for the dynamical evolution of the early Solar System and for the delivery of water and other volatiles to the Earth. |
