Pioneering Heavy Water Detection Suggests Earth's Water Might Be Older Than The Sun

The origin of water on Earth is a complex affair. Was it trapped in the rocks that formed our planet or was it brought by comets and asteroids afterwards? We do not know for sure, but we can move the question even further. Did the water form with the Sun and the planet, or is it even older than that? A new discovery might hold the answer.

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Standard water is made of two hydrogen atoms and one oxygen atom. But there is a version of hydrogen called deuterium. Just like hydrogen, it has one proton and one electron, but it also has one neutron, making it heavier. Water made of two deuterium atoms and one oxygen is known as heavy water.

Heavy water is often associated with nuclear power plants, but it exists in nature. It is in regular water we drink as a minuscule quantity, and it has been found in space as well. Now, researchers report for the first time the detection of heavy water in a protoplanetary disk, the material around a young star that will give birth to planets.

Astronomers using the Atacama Large Millimeter Array (ALMA) detected heavy water around the young system V883 Orionis. This system was also the first one where the snow line was directly observed, the region where water becomes solid around a star. Just a few months ago, 17 different complex organic molecules were discovered in this system. Now scientists have found heavy water too.

“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,” Margot Leemker, lead author on this paper and a postdoc at the University of Milan, said in a statement. “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 team measured the ratio between heavy water and normal water. They found that it is consistent with water being older than the star system. This is the first direct evidence of water being able to survive stellar and planetary formation, suggesting that the water on our planet might be older than the Sun itself.

“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,” said John Tobin, a scientist with the US National Science Foundation National Radio Astronomy Observatory (NRAO), and second author on this new paper. 

The study is published in Nature Astronomy.