A D/H Ratio Consistent With Earth’s Water In Halley-type Comet 12P From ALMA HDO Mapping

The D/H ratio in particular, helps reveal the relationship between (and heritage of) different H₂O reservoirs within the Solar System. Here we present interferometric maps of water (H₂O) and semiheavy water (HDO) in the gas-phase coma of a comet (Halley-type comet 12P/Pons-Brooks), obtained using the Atacama Large Millimeter/submillimeter Array (ALMA).

The maps are consistent with outgassing of both H₂O and HDO directly from the nucleus, and imply a coma D/H ratio (for water) of (1.71±0.44)×10⁻⁴.

This is at the lower end of the range of previously-observed values in comets, and is consistent with D/H in Earth’s ocean water. Our results suggest a possible common heritage between a component of the Oort cloud’s water ice reservoir, and the water that was delivered to the young Earth during the early history of the Solar System.

M. A. Cordiner, E. L. Gibb, Z. Kisiel, N. X. Roth, N. Biver, D. Bockelée-Morvan, J. Boissier, B. P. Bonev, S. B. Charnley, I. M. Coulson, J. Crovisier, M. N. Drozdovskaya, K. Furuya, M. Jin, Y.-J. Kuan, M. Lippi, D. C. Lis, S. N. Milam, C. Opitom, C. Qi, A. J. Remijan

Comments: Published in Nature Astronomy, 8 August 2025
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2508.05925 [astro-ph.EP] (or arXiv:2508.05925v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2508.05925
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Related DOI:
https://doi.org/10.1038/s41550-025-02614-7
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Submission history
From: Martin Cordiner PhD
[v1] Fri, 8 Aug 2025 01:15:34 UTC (1,521 KB)
https://arxiv.org/abs/2508.05925

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