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Abstract 46P/Wirtanen is a Jupiter-family comet, probably originating from the solar system’s Kuiper Belt, that now resides on a 5.4 yr elliptical orbit. During its 2018 apparition, comet 46P passed unusually close to the Earth (within 0.08 au), presenting an outstanding opportunity for close-up observations of its inner coma. Here we present observations of HCN, H13CN, and HC15N emission from 46P using the Atacama Compact Array. The data were analyzed using the SUBLIME non-LTE radiative transfer code to derive12C/13C and14N/15N ratios. The HCN/H13CN ratio is found to be consistent with a lack of significant13C fractionation, whereas the HCN/HC15N ratio of 68 ± 27 (using our most conservative 1σuncertainties), indicates a strong enhancement in15N compared with the solar and terrestrial values. The observed14N/15N ratio is also significantly lower than the values of ∼140 found in previous comets, implying a strong15N enrichment in 46P’s HCN. This indicates that the nitrogen in Jupiter-family comets could reach larger isotopic enrichments than previously thought, with implications for the diversity of14N/15N ratios imprinted into icy bodies at the birth of the solar system.
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This content will become publicly available on August 8, 2026
A D/H ratio consistent with Earth’s water in Halley-type comet 12P from ALMA HDO mapping
Isotopic measurements of Solar System bodies provide a primary paradigm within which to understand the origins and histories of planetary materials. The deuterium-to-hydrogen (D/H) ratio, in particular, helps reveal the relationship between (and heritage of) di erent 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. The maps are consistent with outgassing of both H2O and HDO directly from the nucleus, and they 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 indicate a possible common heritage between a component of the water ice reservoir in the Oort cloud and the water that was delivered to the young Earth during the early history of the Solar System
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- Award ID(s):
- 2009398
- PAR ID:
- 10653018
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- Springer Nature
- Date Published:
- Journal Name:
- Nature Astronomy
- Volume:
- 9
- Issue:
- 10
- ISSN:
- 2397-3366
- Page Range / eLocation ID:
- 1476 to 1485
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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