For the first time, astronomers have studied the atmospheres of planets outside the solar system.

The team led by Mark Swain of NASA’s Jet Propulsion Laboratory in the U.S. spotted evidence of methane gas in the atmosphere of the planet HD 189733b using a method which subtracts the effects of Earth’s atmosphere.

Mr. Swain and his colleagues showed that by looking at different set of light wavelengths, methane and possibly other components can be catalogued using relatively small, Earth-bound telescopes.

The team with the help NASA’s Infrared Telescope Facility in Hawaii measured the light emitted by HD 189733b at two positions — first, when the exoplanet was behind its parent star and second, when it is between its star and the Earth.

The team then subtracted the first measurement from the second. What results is the light due solely to the planet, according to a report in journal ‘Nature’

“Up until this point we’ve not been able to use ground-based telescopes to detect molecules in an exoplanet’s atmosphere,” Mr. Swain was quoted as saying by the BBC News.

To overcome the effects of the earth’s atmosphere — atmospheric gases and passing clouds — the team decided to look in the infrared part of the light spectrum, a region that is not currently covered by space-based telescopes.

Noting that the technique could be extended to other ground-based telescopes, Mr. Swain said, “The work could assist the search for Earth-like planets with traces of organic, or carbon-rich, molecules”.

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