Astronomers have used a new ground-based technique to study the atmospheres of planets outside our Solar System. The work could assist the search for Earth-like planets with traces of organic or carbon-rich molecules. Astronomers spotted evidence of methane gas in the atmosphere of an exoplanet. The technique could be extended to other ground-based telescopes.Methane was first spotted on HD 189733b in 2008 by a group led by Mark Swain of Nasa's Jet Propulsion Laboratory in the U.S. It marked the first time that an organic molecule had been detected on an exoplanet. The known planets residing outside our Solar System number more than 400.