Astronomers have detected gaseous water in the planet-forming disc around the star V883 Orionis.
Using the Atacama Large Millimeter/submillimeter Array (ALMA) they found that this water carries a chemical signature that explains the journey of water from star-forming gas clouds to planets, and supports the idea that water on Earth is even older than our Sun.
“We can now trace the origins of water in our Solar System to before the formation of the Sun,” says John J. Tobin, an astronomer at the National Radio Astronomy Observatory, USA, and lead author of the study published today in Nature.
This discovery was made by studying the composition of water in V883 Orionis, a planet-forming disc about 1300 light-years away from Earth. When a cloud of gas and dust collapses it forms a star at its centre. Around the star, material from the cloud also forms a disc. Over the course of a few million years, the matter in the disc clumps together to form comets, asteroids, and eventually planets. Tobin and his team used ALMA, in which the European Southern Observatory (ESO) is a partner, to measure chemical signatures of the water and its path from the star-forming cloud to the planets.
Water usually consists of one oxygen atom and two hydrogen atoms. Tobin’s team studied a slightly heavier version of water where one of the hydrogen atoms is replaced with deuterium — a heavy isotope of hydrogen.
The journey of water from clouds to young stars, and then later from comets to planets have previously been observed, but until now the link between the young stars and comets was missing. “V883 Orionis is the missing link in this case,” says Tobin. “The composition of the water in the disc is very similar to that of comets in our own Solar System. This is confirmation of the idea that the water in planetary systems formed billions of years ago, before the Sun, in interstellar space, and has been inherited by both comets and Earth, relatively unchanged.”