Tracing the Origins of Water in the Solar System: Insights from the Orionis Disc

ESO, 8 March 2023 - Astronomers have made an incredible discovery about water in the universe. Using a powerful telescope called the Atacama Large Millimeter/submillimeter Array (ALMA), they have found gaseous water in a planet-forming disc around a star called V883 Orionis, located 1300 light-years away from Earth. This discovery reveals the missing link in 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.

The discovery was made by studying the composition of water in the V883 Orionis disc, which is formed by a cloud of gas and dust that collapses to form a star at its center. Material from the cloud also forms a disc around the star, which over time clumps together to form comets, asteroids, and eventually planets. The team used ALMA to measure chemical signatures of the water and its path from the star-forming cloud to planets.

Water usually consists of one oxygen atom and two hydrogen atoms, but the team studied a slightly heavier version of water where one of the hydrogen atoms is replaced with deuterium - a heavy isotope of hydrogen. This ratio of simple and heavy water can be used to trace when and where the water was formed. Tobin’s team found that the composition of the water in the disc is very similar to that of comets in our own Solar System, confirming 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.

Observing the water in the V883 Orionis disc was challenging since most of the water in planet-forming discs is frozen out as ice, making it hidden from view. But thanks to a recent study showing that the V883 Orionis disc was unusually hot, the team was able to detect gaseous water. They found that this disc contains at least 1200 times the amount of water in all Earth’s oceans!

ALMA images of the disc around the star V883 Orionis, showing the spatial distribution of water (left, orange), dust (middle, green) and carbon monoxide (blue, right). Credit:ALMA (ESO/NAOJ/NRAO), J. Tobin, B. Saxton (NRAO/AUI/NSF)

The team hopes to use ESO’s upcoming Extremely Large Telescope and its first-generation instrument METIS in the future. This mid-infrared instrument will be able to resolve the gas-phase of water in these types of discs, strengthening the link of water’s path all the way from star-forming clouds to solar systems. This is an exciting discovery that sheds light on the origins of water in our Solar System and beyond. (Source: ESO)
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