Washington, March 20 : The Hubble Space Telescope has found the tell-tale signature of the molecule methane in the atmosphere of a Jupiter-sized planet HD 189733b, which 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.
The discovery comes after extensive observations made in May 2007 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 made originally by NASA's Spitzer Space Telescope in 2007.
"With this observation, there is no question whether there is water or not - water is present", said Mark Swain of NASA's Jet Propulsion Laboratory (JPL), Pasadena, USA.
The planet, HD 189733b, now known to have methane and water vapour, is located 63 light-years away in the constellation Vulpecula, the little fox.
HD 189733b, a "hot Jupiter"-type extrasolar planet, is so close to its parent star that it takes just over two days to complete an orbit. "Hot Jupiters" are the size of Jupiter but orbit closer to their stars than the tiny innermost planet Mercury in our Solar System.
HD 189733b's atmosphere swelters at 900 degrees C, about the same temperature as the melting point of silver.
The observations were made as the planet HD 189733b 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 starlight from the star HD 189733.
According to co-author Giovanna Tinetti from the University College London and the European Space Agency: "Water alone could not explain all the spectral features observed. The additional contribution of methane is necessary to fit the Hubble data".
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," said Swain.