The first-ever detection of heavy water in a planet-forming disk around a young star proves that the water predates the star itself – and it appears the substance even came from the cold, dark molecular cloud that gave birth to the star.
Scientists have spotted heavy water (which we’ll get to in a moment) in the planet-forming disk of gas and dust around the young star V883 Orionis in ALMAthe Atacama Large Millimeter/submillimeter Array, which is an array of 66 satellite dishes in Chile. V883 Ori is located at 1,350 light years far away and is part of a star cluster born from the famous Orion Nebula.
Now here’s what heavy water is.
Ordinary water is made up of two atoms hydrogen and an oxygen atom. Hydrogen is made from a single proton orbited by a electron. However, the nuclei of some hydrogen atoms have a proton and a neutronAlso. We describe atoms with extra neutrons as an isotope of this element, and the isotope of hydrogen with a neutron is called deuterium. Its atomic mass is slightly greater than that of ordinary hydrogen, thanks to this extra neutron.
Heavy water therefore replaces its two regular hydrogen atoms with two deuterium atoms. We have heavy water in our own solar systemfound for example in comets – and the ratio between heavy water and ordinary water in a cometary body can tell us about the history of its formation.
“Until now, we did not know whether most of the water in comets and planets formed freshly in young disks like V8783 Ori, or whether it was pristine, originating from ancient interstellar clouds,” John Tobin of the US National Radio Astronomy Observatory said in a report. statement.
ALMA’s observations provided the answer. Violent shocks and explosions of young people stars destroys heavy water in a planet-forming disk, allowing it to reform as ordinary water. If this had happened around V883 Ori, the ratio of heavy water to ordinary water would be low, similar to what we find in our solar system.
However, the ratio measured by ALMA in V883 Ori’s disk is the same as that observed in clusters of molecular gases before they form stars or planets. In fact, the ratio is twice as high as it would be if the water had been broken up and reformed in the disk.
“Our detection demonstrates beyond doubt that the water observed in this planet-forming disk must be older than the central star and formed in the early stages of star and planet formation,” said Margot Leemker of the University of Milan, who led the study. “This represents a major advance in understanding the journey of water through planet formation and how that water made its way to our solar system and eventually Earth, through similar processes.”
This means that the water is older than the star – it could actually be billions of years older, having remained all this time in the molecular cloud that became the Orion Nebula as ice covering tiny grains of dust.
V883 Ori is only half a million years old, and water was first detected in its planet-forming circumstellar disk in 2023. No planets have yet been detected in this disk, although any comets that may have already formed will reflect this high rate of heavy water. The star’s young age means it hasn’t yet had enough time for its old water to be reprocessed by heating in the disk, but that time will come soon, as explosions of the young star have already been observed – for example, in 2016, when ALMA studied the effect of the explosion on the snow line, or where water changes from steam to ice, in V883 Ori’s disk.
“The detection of heavy water…proves the ancient heritage of water and provides a missing link between clouds, disks, comets and ultimately planets,” Tobin said. “This discovery is the first direct evidence of interstellar travel of water, from clouds to the materials that form planetary systems, unchanged and intact.”
The results were published October 15 in the journal Natural astronomy.
