Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have detected gaseous water in the planet-forming disk around V883 Orionis, a protostar located 1,305 light-years away in the constellation of Orion. 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.
Water usually consists of one oxygen atom and two hydrogen atoms.
Dr. John Tobin, an astronomer at NSF’s National Radio Astronomy Observatory, and his colleagues studied a slightly heavier version of water where one of the hydrogen atoms is replaced with deuterium — a heavy isotope of hydrogen.
Because simple and heavy water form under different conditions, their ratio can be used to trace when and where the water was formed.
For instance, this ratio in some Solar System comets has been shown to be similar to that in water on Earth, suggesting that comets might have delivered water to Earth.
“We can think of the path of water through the Universe as a trail,” Dr. Tobin said.
“We know what the endpoints look like, which are water on planets and in comets, but we wanted to trace that trail back to the origins of water.”
“Before now, we could link the Earth to comets, and protostars to the interstellar medium, but we couldn’t link protostars to comets.”
“V883 Ori has changed that, and proven the water molecules in that system and in our Solar System have a similar ratio of deuterium and hydrogen.”
Observing water in the circumstellar disks around protostars is difficult because in most systems water is present in the form of ice.
When astronomers observe protostars they’re looking for the water snow line or ice line, which is the place where water transitions from predominantly ice to gas, which radio astronomy can observe in detail.
“If the snow line is located too close to the star, there isn’t enough gaseous water to be easily…
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