Constraints on the Formation Regions of Comets from their D:H Ratios |
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Authors: | Jonathan Horner Olivier Mousis Franck Hersant |
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Institution: | 1. Physikalisches Institut, University of Bern, Sidlerstrasse 5, CH-3012, Bern, Switzerland 2. Observatoire de Besan?on, CNRS-UMR 6091, BP 1615, 25010, Besan?on Cedex, France 3. LESIA, Observatoire de Meudon, CNRS-UMR 8109, 5 Place Jules Janssen, 92195, Meudon Cedex, France
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Abstract: | Studies of the D:H ratio in H2O within the Solar nebula provide a relationship between the degree of enrichment of deuterium and the distance from the young
Sun. In the context of cometary formation, such models suggest that comets which formed in different regions of the Solar
nebula should have measurably different D:H ratios. We aim to illustrate how the observed comets can give information about
the formation regions of the reservoirs in which they originated. After a discussion of the current understanding of the regions
in which comets formed, simple models of plausible formation regions for two different cometary reservoirs (the Edgeworth–Kuiper
belt and the Oort Cloud) are convolved with a deuterium-enrichment profile for the pre-solar nebula. This allows us to illustrate
how different formation regions for these objects can lead to great variations in the deuterium enrichment distributions that
we would observe in comets today. We also provide an illustrative example of how variations in the population within a source
region can modify the resulting observational profile. The convolution of a deuterium-enrichment profile with examples of
proto-cometary populations gives a feel for how observations could be used to draw conclusions on the formation region of
comets which are currently fed into the inner Solar system from at least two reservoirs. Such observations have, to date,
been carried out on only three comets, but future work with instruments such as ALMA and Herschel should vastly improve the
dataset, leading to a clearer consensus on the formation of the Oort cloud and Edgeworth–Kuiper belt. |
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Keywords: | Comets: general Kuiper Belt Oort Cloud Solar system: formation |
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