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Applicant -- Measurements of the D/H ratio in water in comets

Monday, July 30, 2018
de Val-Borro

Having preserved pristine material from the original solar nebula, comets
provide unique clues about the history and evolution of the Solar System.
Water, one of the main components of the comet's nucleus, plays a
crucial role in the thermodynamics of cometary comae activity and
is an essential element for the occurrence of life.  By measuring the D/H ratio
in water in a sample of comets constraints can be placed on the conditions
under which icy planetesimals formed and the contribution of comets to the
delivery of volatiles to the Earth.  The observed range of D/H ratios in
members of the Oort-cloud and Jupiter-family comets indicate that an unexpected
isotopic diversity is present in the comet population, having different
deuterium enrichment factors by a factor of 3, and consistent in two objects
with the standard mean ocean water value.  Isotopic variations in comets may be
expected if planetesimals underwent large-scale mixing during the planetary
migration early in the Solar System history.  However, the poor statistics of
the sample and additional observational biases prevents a stringent comparison
with models. Finally, I discuss prospects for measuring precisely the D/H ratio
in comets using ALMA to investigate deuterium enrichment in cometary water and
improve our understanding of the origin of water on Earth.

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