Herschel space telescope detects abundant water around young star
Using the Herschel space telescope, astronomers have for the first time found cold water vapour in the planet-forming disc around a young star. This indicates that the disc contains large quantities of water. There may be many more planets with water in the universe. The research team of Leiden astronomer Michiel Hogerheijde published their findings in Science.
Astronomers had already in the past detected hot water vapour in planet-forming discs, close to the central star. But until now there was no direct evidence that large quantities of water extended to the cold outer parts of such discs. The more water is available there to form ice-laden comets, the higher the chance that large quantities of water will eventually, as a result of comet bombardment, find their way to newly formed planets.
‘Our observations of this cold water vapour show that there is enough water in the disc to fill thousands of Earth oceans,’ says first author Michiel Hogerheijde. ‘The same situation probably arose during the formation of our own solar system 4.6 billion years ago: comet bombardment also played an important part in the formation of oceans on Earth.’
The discovery was made in the vicinity of TW Hydrae, a star barely 175 light-years away from our solar system, in the aptly named constellation Hydra (water snake). Hogerheijde and his research team think that the icy mist that they discovered originated in ice-covered dust particles near the surface of the disc. UV light from the star releases a small quantity of water from the ice and forms a thin layer of vapour, which can be detected by Herschel’s infrared instrument HIFI.
‘These are the most sensitive measurements ever made using HIFI, and the makers of the instrument deserve our compliments that such weak signals can be detected,’ says Leiden astronomer Ewine van Dishoeck, who co-authored the Science article, together with Amsterdam astronomer Carsten Dominik.
The barely 10 million years old star TW Hydrae is surrounded by a disc of dust and gas, that measures approximately 200 times the length of the distance between the Earth and the sun. The ice-covered particles in the disc are expected in the next couple of millions of years to condense to form planets, asteroids and comets. The latter, essentially dirty snowballs, can, through impact, deliver their water supply to newly formed, dry-as-a-bone planets, and furnish them with oceans. Whether TW Hydrae and its icy disc are indeed representative of other newly formed stars, which astronomers believe to be the case, can be determined through further research using HIFI on three other stars.
Herschel is a mission of the European Space Organisation ESA, with contributions from the American Space Organisation NASA. The telescope was launched in 2009 and it has three instruments on board, including the spectrometer for the far infrared HIFI, which was designed among other things to find water in widely divergent objects. The instrument is able to provide a precise chemical identification of atoms and molecules and is therefore pre-eminently suitable to study the chemistry of young and old stars. HIFI was built in the Netherlands by an international consortium led by the SRON space research institute.
Fundamentals of Science research profile area
(24 October 2011)