Astronomers using ESA’s Herschel Space Observatory have discovered huge amounts of water vapor in a cold pre-stellar core in the constellation of Taurus known as Lynds 1544, enough to fill Earth’s oceans more than 2000 times over.

Water, essential to life on Earth, has previously been detected outside of the Solar system as gas and ice coated onto tiny dust grains near sites of active star formation, and in proto-planetary discs capable of forming alien planetary systems.

The new observations of Lynds 1544, described in a paper accepted for publication in the Astrophysical Journal Letters (arXiv.org version), are the first detection of water vapor in a molecular cloud on the verge of star formation. More than 2000 Earth oceans-worth of water vapor were detected, liberated from icy dust grains by high-energy cosmic rays passing through the cloud.

“To produce that amount of vapor, there must be a lot of water ice in the cloud, more than three million frozen Earth oceans’ worth,” said lead author Dr Paola Caselli of the University of Leeds. “Before our observations, the understanding was that all the water was frozen onto dust grains because it was too cold to be in the gas phase and so we could not measure it. Now we will need to review our understanding of the chemical processes in this dense region and, in particular, the importance of cosmic rays to maintain some amount of water vapor.”

The observations also revealed that the water molecules are flowing towards the heart of the cloud where a new star will probably form, indicating that gravitational collapse has just started.

“There is absolutely no sign of stars in this dark cloud today, but by looking at the water molecules, we can see evidence of motion inside the region that can be understood as collapse of the whole cloud towards the center,” Dr Caselli said. “There is enough material to form a star at least as massive as our Sun, which means it could also be forming a planetary system, possibly one like ours.”

Some of the water vapor detected in Lynds 1544 will go into forming the star, but the rest will be incorporated into the surrounding disc, providing a rich water reservoir to feed potential new planets.

“Thanks to Herschel, we can now follow the ‘water trail’ from a molecular cloud in the interstellar medium, through the star formation process, to a planet like Earth where water is a crucial ingredient for life,” explained ESA’s Herschel project scientist Dr Göran Pilbratt.

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Bibliographic information: Paola Caselli et al. 2012. First detection of water vapor in a pre-stellar core. Accepted for publication in the Astrophysical Journal Letters; arXiv: 1208.5998