The first-ever detection of doubly deuterated water (D_2O), or “heavy water,” in a planet-forming disk was made around the young star V883 Orionis using the Atacama Large Millimeter/submillimeter Array (ALMA).
This discovery is a major breakthrough because it provides the first direct evidence that the water found in this disk—and by extension, the water that forms comets and planets like Earth—is ancient and older than the central star itself.
Key Findings and Significance
The detection of heavy water serves as a “chemical fossil” that connects the water in a developing solar system back to the earliest stages of star and planet formation:
• Ancient Heritage: The ratio of heavy water (D_2O) to normal water (H_2O) in the V883 Ori disk matches the ratio found in ancient interstellar clouds, which are the frigid nurseries where stars are born. This high ratio is a strong indicator that the water formed in the extreme cold of the interstellar medium, surviving the star’s birth intact.
• A Missing Link: This finding provides the missing link in the journey of water, demonstrating that it can travel from ancient interstellar clouds, through the protoplanetary disk, and ultimately into comets and planets without being destroyed or chemically reset.
• Origin of Earth’s Water: The discovery strongly suggests that a significant amount of the water in our own Solar System, possibly including the water in Earth’s oceans, was inherited from the interstellar medium and is billions of years older than the Sun.
What is Heavy Water?
Heavy water is a common term for water molecules where one or both of the hydrogen atoms (^1H, or protium) are replaced by its heavier isotope, deuterium (^2H, or D). Deuterium is often called “heavy hydrogen” because its nucleus contains one proton and one neutron, giving it roughly double the mass of protium’s single-proton nucleus.
The type of heavy water detected in the V883 Ori disk was doubly deuterated water (D_2O), where both hydrogen atoms are deuterium.
The presence and specific abundance ratio of these heavier water molecules are essential to astronomers because they act as a signature of the extremely cold temperatures required for their formation.
Our detection indisputably demonstrates that the water seen in this planet-forming disk must be older than the central starand formed at the earliest stages of star and planet formation,” shares Margot Leemker, lead author on this paper, and a postdoc with the Department of Physics, 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.”
Does this mean that the water in your morning cup of coffee could be older than the sun? The chemical fingerprinting of D₂O shows that these water moleculeshave survived the violent processes of star and planet formation, traveling billions of kilometers through space and time before, ending up in planetary systems like our own. Instead of being destroyed and reformed in the disk, the bulk of this water is inherited from the earliest, coldest stages of star formation, a cosmic hand-me-down that may also be present on Earth today.
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,” shares John Tobin, a scientist with the U.S. National Science Foundation National Radio Astronomy Observatory, and the second author on this new paper.
Water is fundamental to life and habitability. Knowing where planetary water comes from helps us understand the ingredients for life in our solar system and in others. This discovery suggests that many young planets, and maybe even worlds beyond our own, could inherit water billions of years older than themselves, reminding us how deeply interconnected our existence is with the universe’s ancient past.
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