A Herschel Study of D/H in Water in the Jupiter-Family Comet 45P/Honda-Mrkos-Pajdušáková and Prospects for D/H Measurements with CCAT

Abstract

We present Herschel observations of water isotopologues in the atmosphere of the Jupiter-family comet 45P/Honda–Mrkos–Pajdušáková. No HDO emission is detected, with a 3σ upper limit of 2.0 × 10^(−4) for the D/H ratio. This value is consistent with the earlier Herschel measurement in the Jupiter-family comet 103P/Hartley 2. The canonical value of 3 × 10^(−4) measured pre-Herschel in a sample of Oort-cloud comets can be excluded at a 4.5σ level. The observations presented here further confirm that a diversity of D/H ratios exists in the comet population and emphasize the need for additional measurements with future ground-based facilities, such as CCAT, in the post-Herschel era.

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