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

TL;DR

This study uses Herschel data to measure water isotopologues in comet 45P, finding no HDO emission and supporting the diversity of D/H ratios among comets, highlighting future measurement prospects with CCAT.

Contribution

It provides the first D/H ratio upper limit for comet 45P and compares it with other comets, emphasizing the diversity of D/H ratios and future measurement opportunities.

Findings

No HDO emission detected in 45P.

D/H ratio consistent with other Jupiter-family comets.

Canonical D/H value in Oort-cloud comets excluded at 4.5 sigma.

Abstract

We present Herschel observations of water isotopologues in the atmosphere of the Jupiter-family comet 45P/Honda-Mrkos-Pajdusakova. No HDO emission is detected, with a 3 sigma 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 4.5 sigma 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.