Astronomers have detected doubly deuterated water, a form of “heavy water,” in a planet-forming disk for the first time, adding to evidence that some of the water in our Solar System predates the Sun itself. The discovery provides new insight into how ancient interstellar ice survived the violent birth of stars and planetary systems.

Using the Atacama Large Millimeter/submillimeter Array (ALMA), researchers identified doubly deuterated water (D2O) in the disk surrounding V883 Orionis, a young Sun-like star. The presence of this rare isotopic form of water shows that the water in the disk – and the comets and planets that may one day emerge from it – originated long before the star’s formation.

“Our detection indisputably demonstrates that the water seen in this planet-forming disk must be older than the central star and formed at the earliest stages of star and planet formation,” said Margot Leemker, lead author of the study and a postdoctoral researcher at the University of Milan. “This presents a major breakthrough in understanding the journey of water through planet formation, and how this water made its way to our Solar System, and possibly Earth, through similar processes.”

The chemical fingerprint of D2O provides strong evidence that the disk’s water was inherited from ices formed in cold molecular clouds before the star. Instead of being destroyed and reconstituted during the disk’s evolution, they survived intact – cosmic relics passed from interstellar space to newborn planetary systems.

“Until now, we weren’t sure if most of the water in comets and planets formed fresh in young disks like V883 Ori, or if it’s ‘pristine,’ originating from ancient interstellar clouds,” explained John Tobin, co-author and scientist at the U.S. National Science Foundation’s National Radio Astronomy Observatory.

The detection strengthens the link between interstellar clouds, planet-forming disks and comets, as described in the observatory operator’s account of the research.

It also adds weight to the view that the water found in comets, and perhaps in Earth’s oceans, is inherited rather than newly created. If so, some Solar System water predates the Sun, linking star formation to the origins of life-supporting environments.

Research Report:Pristine ices in a planet-forming disk revealed by heavy water