'Oceans' of water discovered in space

Artist's conception of the TW Hydrae system Image credit: NASA/JPL-Caltech

Last week, NASA announced that water-covered planets, like Earth, may be common in the universe. This is because a team of scientists, led by Dutch astronomer Michiel Hogerheijde, have recently discovered cold water vapour surrounding the orange dwarf star TW Hydrae. Their findings have been published in the October 21 issue of Science and can be read for free here.

Planets and asteroids form from the disk of dust and gas that surrounds newly formed stars, known as a protoplanetary disk. Since this matter is unevenly distributed, gravitational interactions cause it to clump together forming pebbles, boulders and, after millions of years of collisions, spherical planets. Planets that form closest to the star are warm and rocky, whilst those that are further away are cold and gaseous.

At 176 light years away, TW Hydrae contains the closest protoplanetary disk to Earth. It extends to almost 200 AU, where 1 AU is the distance between the Earth and Sun. This is over 6 times further than the distance between the Sun and Neptune.

Scientists have previously found hot water within the protoplanetary disks of young stars, but this boils away before any planets have time to form. The water surrounding TW Hydrae has formed so far out that it has frozen. Ultraviolet light causes about one molecule in a million to break free, forming a thin layer of water vapour. Over 7,000 quintillion (a billion, billion) kilograms of this vapour have been directly detected by the European Space Agency's Herschel Space Observatory. This implies that the TW Hydrae system contains enough ice to fill the Earth's oceans several thousand times over. In the next few million years, this ice is expected to form clouds of comets which will eventually transport the water to newly formed planets.

Although the origin of water on Earth is still a mystery, it is thought that some was formed along with the planet and the rest was brought to Earth with impacting comets. It has even been suggested that life could not have formed on Earth without comets since they are also known to contain amino acids, the 'building blocks of life'.

Image credit: NASA/National Geographic

The TW Hydrae system is thought to be representative of many other protoplanetary systems. Earlier this year, scientists at NASA predicted that about 500 million planets in our galaxy may be capable of containing life and these new findings suggest that many could be 'water planets', containing vast oceans.

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