An astronomer utilizing the Atacama Large Millimeter/Submillimeter Array (ALMA) has discovered double deuterated water (D2O), commonly known as “heavy water,” in the protoplanetary disk surrounding the protostar V883 Orionis, situated 1,300 light-years away in the Orion constellation. This finding indicates that some of the water found in comets—and even on Earth—might predate the stars themselves, offering transformative insights into the history of water in our solar system.
This artist’s impression illustrates the evolution of heavy water molecules, previously detected in giant molecular clouds, planet-forming disks, and comets, before ultimately reaching Earth. Image credit: NSF / AUI / NRAO of NSF / P. Vosteen / B. Saxton.
Investigating the primordial material from the protoplanetary disk that gave rise to our solar system suggests that water may have been transported to Earth via comet or asteroid impacts.
However, it remains uncertain whether the water ice present on these celestial objects formed primarily during the protoplanetary disk phase or if it is considerably older, originating from parent molecular clouds.
“This detection clearly demonstrates that the water found in the planet-forming disk around V883 Orionis predates the central star and must have formed during the early phases of star and planet formation,” stated Dr. Margot Rehmker, an astronomer at the University of Milan.
“This marks a significant leap in our understanding of the journey of water throughout planet formation and how this water potentially reached the solar system, including Earth, through similar mechanisms.”
The chemical fingerprinting of heavy water indicates that these molecules have withstood the turbulent processes of star and planet formation, traversing billions of kilometers through the cosmos and ending up in planetary systems like ours.
Rather than being completely destroyed and reformed within the disk, a significant portion of this water is inherited from the earliest, most frigid stages of star formation, serving as a cosmic remnant that may still exist on Earth today.
“Until now, it was uncertain whether most of the water in comets and planets was newly formed in young disks such as Orionis V883 or whether it was ‘pure’ from ancient interstellar clouds,” remarked Dr. John Tobin, an astronomer at the NSF National Radio Astronomy Observatory.
“The detection of heavy water using sensitive isotopic isomer ratios (D2oh2O) validates that this water is an ancient relic, forming a crucial link between clouds, disks, comets, and planets.”
“This finding is the first direct evidence that water can traverse through stars unaltered and intact, moving from clouds to the materials that constitute planetary systems.”
The team’s paper is published in this week’s edition of Nature Astronomy.
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M. Riemker et al. Primitive ice within a planet-forming disk identified by heavy water. Nat Astron published online October 15, 2025. doi: 10.1038/s41550-025-02663-y
Source: www.sci.news
