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Hubble finds first organic molecule on extrasolar planet 
The NASA/ESA Hubble Space Telescope has made the first detection ever of an organic molecule in the atmosphere of a planet orbiting another star. This breakthrough is an important step in eventually identifying signs of life on a planet outside our Solar System. Hubble found the tell-tale signature of methane in the atmosphere of the Jupiter-sized extrasolar planet HD 189733b. Under the right circumstances, methane can play a key role in prebiotic chemistry – the chemical reactions considered necessary to form life as we know it. Although methane has been detected on most of the planets in our Solar System, this is the first time any organic molecule has been detected on a world orbiting another star. This discovery proves that Hubble and upcoming space missions, such as the NASA/ESA/CSA James Webb Space Telescope, can detect organic molecules on planets around other stars using spectroscopy, which splits light into its components to reveal the fingerprints of various chemicals.
The discovery comes after extensive observations in May 2007 carried out with Hubble’s Near Infrared Camera and Multi-Object Spectrometer (NICMOS). It also confirms the existence of water molecules in the planet’s atmosphere, a discovery originally made by co-author Giovanna Tinetti in 2007 while she was an ESA fellow at Institute d’Astrophysique de Paris, France, using NASA’s Spitzer space telescope. “With this observation there is no question whether there is water or not – water is present”, said Swain.
The observations were made as the planet passed in front of its parent star in what astronomers call a transit. As the light from the star passed briefly through the atmosphere along the edge of the planet, the gases in the atmosphere imprinted their unique signatures on the light from the star HD 189733. Giovanna Tinetti, now affiliated to University College added, “Water alone could not explain all the spectral features observed. The additional contribution of methane is necessary to fit the Hubble data”.
Tinetti is however quick to rule out any biological origin of the methane found on HD 189733b. “The planet’s atmosphere is far too hot for even the hardiest life to survive — at least the kind of life we know from Earth. It’s highly unlikely that cows could survive here!” The astronomers were surprised to find that the planet has more methane than predicted by conventional models for hot Jupiters. This type of hot planet should have much more carbon monoxide than methane but HD 189733b doesn’t.
Although this star-hugger is too hot for life as we know it, “this observation is proof that spectroscopy can eventually be done on a cooler and potentially habitable Earth-sized planet orbiting a dimmer red dwarf-type star”, Swain said. The ultimate goal of studies like these is to identify prebiotic molecules in the atmospheres of planets in the habitable zones around other stars, where temperatures are right for water to remain liquid rather than freeze or evaporate away. “These measurements are an important step to our ultimate goal of determining the conditions, such as temperature, pressure, winds, clouds, etc., and the chemistry on planets where life could exist. Infrared spectroscopy is really the key to these studies because it is best matched to detecting molecules”, said Swain. Notes for editors: The paper ‘Methane present in an extrasolar planet atmosphere’ by Mark Swain, Gautam Vasisht and Giovanna Tinetti is being published in the 20 March issue of the journal Nature. Giovanna Tinetti was an ESA Research Fellow at University College London until October 2007, where she is now based. The Hubble Space Telescope is a project of international cooperation between ESA and NASA. For more information: Giovanna Tinetti, University College London, UK Email: G.Tinetti @ ucl.ac.uk Mark Swain, Jet Propulsion Laboratory, Pasadena, California, USA Email: Swain @ s383.jpl.nasa.gov Lars Lindberg Christensen, Hubble/ESA, Garching, Germany E-mail: Lars @ eso.org Ray Villard, Space Telescope Science Institute, Baltimore, USA E-mail: Villard @ stsci.edu
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