Recent peer-reviewed research analyzing heavy water in protoplanetary disks establishes that water ice originates from the earliest phases of star formation and predates the central star.
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) 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. 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. Detailed mapping of the distribution of water and semiheavy water in the coma of Halley-type comet 12P implies a D/H ratio that is consistent with that of Earth’s water, indicating a common heritage.
Water is essential to our understanding of the planet-formation process and habitability on Earth. Although trace amounts of water are seen across all phases of star and planet formation, the bulk of the water reservoir often goes undetected, hiding crucial parts of its journey from giant molecular clouds to planets. This raises the question of whether water molecules in comets and (exo-)planets is largely inherited from the interstellar medium or whether the water molecules are destroyed and then reformed in the disk. Water isotopologue ratios involving doubly deuterated water (D2O) are a sensitive tracer to answer this question. Here we present strong evidence of inheritance through an enhancement of D2O in the outbursting V883 Ori disk. The high D2O/H2O ratio of (3.2 ± 1.2) × 10−5 is consistent with values seen in protostellar envelopes and a comet and is 2 orders of magnitude higher than expected if water is reprocessed. The high deuteration of the heaviest isotopologues D2O/HDO = (2.3 ± 1.0) × HDO/H2O further establishes the inheritance of water. We conclude that water ice in disks originates from the earliest phases of star formation, providing the missing link between cold dark clouds and (exo-)comets. The origin of water is one biggest unknowns in the field of star and planet formation: is it inherited or created in situ? Through the detection of heavy water (D2O) in a protoplanetary disk, it is shown that this water must be older than the central star.
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