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Boffins find 'missing link' between interstellar ice and what comes out of the tap

Now drink your space juice

It looks likely that the water on Earth is older than the Sun and the stuff we drink today probably isn't all that different than it was over 4.6 billion years ago when our star formed.

Researchers at the US National Radio Astronomy Observatory (NRAO), working with the instruments at Chile's Atacama Large Millimeter/submillimeter Array (ALMA), reached that conclusion based on observations of protostar V883 Orionis, a part of the Orion constellation located around 1,305 light years from Earth. In a paper published in Nature, the boffins say the still-forming star is the missing link to explain how interstellar ice becomes planet-bound water.

"We can think of the path of water through the Universe as a trail. 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," said National Science Foundation NRAO astronomer John Tobin, the lead author of the paper. 

Prior to this research, Tobin said, it was possible to link water on Earth to water in comets, and to observe frozen water in the clouds that form around protostars, but there no link between the two had been recorded. Observations of V883 have changed that, Tobin said, by proving that the ratio of types of water molecules that currently exist in our neck of the woods are similar to those in the under-construction V883 system. 

"We now have an unbroken chain in the lineage of water from comets and protostars to the interstellar medium," Tobin said. 

The water out of space

Inhospitable vacuum though it may be, it's largely accepted that there's plenty of water to be found in the gasses and clouds of interstellar space, mostly frozen ice clinging to the surface of dust particles.

As such particles form clouds, gravity comes into play and sometimes results in clouds collapsing into protostars like V883. The rest of the liquid from the cloud gets stuck in the young star's protoplanetary disk, and from there it ends up on planets or comets as the cloud continues to condense around the star's gravity.

You may be wondering at this point how this proves that the water on Earth is the same water that once floated in the emptiness of space before the formation of our solar system, and that's what Tobin and his team figured out with ALMA.

V883 was an ideal observation target because, unlike many protoplanetary disks that are mostly frozen, V883 has been heating up, which has turned a good portion of its cloud into gasses - perfect for observing with a radio telescope like ALMA. 


An artist's concept of the interstellar disk surrounding V883 Orionis. Source: ALMA (ESO/NAOJ/NRAO), B. Saxton (NRAO/AUI/NSF)

By taking a series of readings using ALMA's Band 5 and Band 6, which operate at 1.6mm and 1.3mm wavelengths, respectively, the team found that the ratio of H2O water and HDO water in the disk was similar to many comets in our solar system's Oort cloud

What all of that means, according to the paper, is that water is "formed on icy dust grains, that the molecules are inherited from the prestellar phase, and that significant chemical reset does not occur during disk or comet formation." 

"This is exciting as it suggests that other planetary systems should have received large amounts of water too," University of Michigan Astronomer Merel van 't Hoff, a co-author on the paper, said. 

So drink that cup of space juice with the knowledge that, even though ALMA might have steered us wrong on the existence of aliens before, these observations mean formerly interstellar liquid may be plentiful on exoplanet surfaces, and just waiting to be found. ®

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