Commenting on this result Professor Keith Mason, CEO of the Science and Technology Facilities Council (STFC) said, "This first conclusive evidence of the presence of water vapour in the atmosphere of a planet beyond our Solar System provides an exciting breakthrough in our knowledge of extra-solar planets. It represents a real step forward into establishing whether we are alone in the Universe or whether there is life on other planets."
Over 200 extra-solar planets are now known, orbiting stars close to our own Sun. The planet which has water in its atmosphere is known as HD189733b, and orbits a star in the constellation of Vulpecula the Fox, which is 63 light years from the Sun. Planet HD 189733b, a gas giant about 15% bigger than Jupiter, is known as a "transiting planet" as it passes directly in front of its star, as viewed from the Earth. Unlike Jupiter, which is over five times as far away from the Sun as our Earth is, HD 189733b is over 30 times closer to its star than the Earth is to the Sun – that's why it is so hot.
The researchers, led by Dr Giovanna Tinetti, an ESA fellow from the Institute d'Astrophysique de Paris and UCL (from 1st July), found that HD 189733b absorbs the starlight of its "sun", as it passes in front, in a way that can only be explained if it has water vapour in its atmosphere. This is the first time that astronomers have demonstrated for certain that water is present in an extra-solar planet with the infrared analysis of the planet's transit across its parent star providing the breakthrough.
Dr Tinetti, who is taking up a prestigious STFC Aurora Fellowship at UCL to study atmospheric signatures and biosignatures on planets beyond our solar system, said; "Although HD 189733b is far from being habitable, and is actually quite a hostile environment, our discovery shows how water might be common out there and how our method can be used in the future to study more life-friendly environments."
Dr Tinetti adds, "The 'holy grail' for today's planet hunters is to find an Earth-like planet that also has water in its atmosphere. That discovery, when it happens, will provide real evidence that planets outside of our Solar System might harbour life. So the discovery that water exists on an extra—solar gas giant is a vital milestone along that road of discovery."
This exciting discovery was made using NASA's Spitzer Earth-orbiting telescope, taking measurements at a number of key wavelengths in the infrared region of the spectrum that pick out the crucial signature of water. The water detection relied not only on Dr Tinetti's painstaking analysis, but also on the calculation of highly accurate water absorption parameters by Dr Bob Barber and Professor Jonathan Tennyson, also from UCL.
Dr Barber said, "Initial data included over 500 million individual absorption features and from this we calculated the absorption parameters. Each feature is unique, like a fingerprint, and provides vital clues about the amount of water present and the temperature of the atmosphere."
Professor Tennyson, who heads UCL's Physics and Astronomy Department, explained: "Parts of the atmosphere of HD 189733b are very hot – around 2000 degrees. You need the millions of lines we calculated to simulate this, putting in absorption accurately where it should be and – just as accurately – giving gaps for the light to get through the atmosphere, where it can."
Link to ESA release (link opens in a new window)|.
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Gill Ormrod
Science and Technology Facilities Council
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Images
Two artists impressions are available illustrating the extra solar planet are available from the ESA website or by contacting Gill Ormrod in the STFC press office – details above.
Nature details
The findings appear in the 12 July 2007 issue of the scientific journal Nature. The paper is called 'Water vapour in the atmosphere of a transiting extrasolar planet', by G.Tinetti, A.Vidal-Madjar, M-C. Liang, J-P. Beaulieu, Y. L. Yung, S. Carey, R.Barber, J. Tennyson, I. Ribas, N. Allard, G. Ballester, D.K. Sing, F.Selsis.
NASA's Jet Propulsion Laboratory (JPL), Pasadena, California, manages the Spitzer Space Telescope for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology (Caltech), also in Pasadena. Caltech manages JPL for NASA.
The Science and Technology Facilities Council's Aurora Fellowship information scheme is dedicated to enhancing the UK's long term capabilities and cross disciplinary approach to planetology and astrobiology. For further details see: the news of Space Science - UK invests for the future (link opens in a new window)|.
