Water Found On Planet Outside Solar System

Water has been found on a planet outside our solar system for the first time - giving scientists a tantalising hint of life beyond Earth.

The planet, known as HD189733b, is a Jupiter like gas giant which is about 60 light years away in the constellation of Vulpeca the Fox.

Using NASA's infrared Spitzer space telescope, astronomers discovered that as the planet orbits its sun it absorbs starlight in a way that can only be explained by the presence of water vapour, or steam, in its atmosphere.

The same side of HD 189733b always faces the host star. It was only discovered in 2005 and appears to have winds that rage around it up to 6,000 mph, which would make it completely inhospitable for life. The jet streams on Earth travel at 200 mph.

Astrophysicist Dr Giovanna Tinetti, of the European Space Agency, said the dramatic discovery increases the chances of life being found among the stars - but probably not on this exotic world. The planet orbits so close to its parent star that its surface reaches a scorching 1,700 F.

Dr Tinetti said: "Although HD189733b is far from being habitable, and actually provides a rather hostile environment, our discovery shows that water might be more common out there than previously thought, and our method can be used in the future to study more 'life friendly' environments."

Her team's findings, published in Nature, have given scientists their first sniffs of air from an alien world and Dr Tinetti, who has just taken up a prestigious Aurora Fellowship at University College London, hopes it is the start of even more exciting discoveries.

She added: "The 'holy grail' for today's planet hunters is to find an Earth like planet that also has water in its atmosphere.

"When it happens, that discovery will provide real evidence that planets outside our Solar System might harbour life. Finding the existence of water on an extra solar gas giant is a vital milestone along that road of discovery."

The mysterious HD189733b belongs to a type of extrasolar planet known as "hot Jupiters". These planets orbit precariously close to their stars and are extremely hot.

The cloudy planet races around its star every 2.2 days. It is more than 30 times closer to its star than the Earth is to the Sun which means temperatures on this balmy world range from 1,200 F on the dark side to a broiling 1,700 F on the sunlit side.

Dr Tinetti said it is possible for water vapour to survive in even hotter temperatures although the existence of any sort of life form would be impossible.

Previous studies of the same planet and of another hot Jupiter HD 209458b, located about 150 light years away in the constellation Pegasus, both found no evidence for water.

More than 200 "extra-solar" planets like HD189733b have been discovered but their close proximity to their own star has made detecting water and other compounds difficult.

Dr Tinetti and colleagues measured the radius of HD189733b at different wavelengths by tracking how much starlight is blocked by the planet as it crosses in front of its parent star.

The planet looked bigger at the wavelength bands that correspond to water, suggesting that water is present in the atmosphere where it absorbs the radiation at these wavelengths.

The researchers took advantage of the fact that HD189733b is a "transiting planet" which means it passes directly in front of its star, as seen from Earth.

When this happens water vapour in the planet's atmosphere causes the planet to appear slightly larger in the infrared part of the starlight than in the visible portion.

A painstaking analysis of measurements at different wavelengths and a calculation of highly accurate water data was able to detect the tell-tale "fingerprints" of water molecules on the planet.

The researchers found the light blocking area of HD189733b is slightly larger when measured at a longer wavelength because the water vapour in the atmosphere absorbs more light. At a shorter wavelength it transmits more light.

Astronomer Heather Knutson, of Harvard University, Massachusetts, said: "Is the presence of water a feature common to all gas giant planets?

"The first convincing detection of water vapour in the atmosphere of such a planet from outside our Solar System indicates that the answer is yes."

Telescope technologies are being developed that will probe the very faint light from other solar systems for tell-tale signs of biology. These are the same "life markers" known to be present in light reflected off the Earth, known as "earthshine".

They include signatures for water, and gases such as oxygen and methane and perhaps more complex molecules such as chlorophyll - the pigment which makes the process of photosynthesis possible.

Dr Tinetti said: "At the moment we are searching for water, and with it the possible existence of alien life, in a very indirect way.

"But space science is moving very fast and the next generation of telescopes over the coming decade should be able to carry out more direct investigations because they will be much more powerful."