Astronomers have peered into the atmosphere of a faraway planet using a telescope in Hawaii, a feat that marks a major step forward in the search for life beyond the solar system.
Until now, scientists have only been able to analyse the atmospheres of such distant worlds using the Hubble and Spitzer space telescopes, which are in orbit around the Earth.
The latest study is the first to observe the atmosphere of a distant planet using a ground-based telescope, proving that these more versatile and powerful instruments can join in the search for extraterrestrial life.
Scientists pointed Nasa's Infrared Telescope Facility at a distant planet called HD 189733b some 63 light years away in the constellation of Vulpecula.
The telescope, which is perched on the summit of Mauna Kea, a volcanic island in Hawaii, picked up signs of methane in the planet's atmosphere that could not be seen by either Hubble or Spitzer. Astronomers detected a bright fluorescent signal, caused by radiation from the nearby star being absorbed by methane and released as light.
The methane signal is similar to those that have been observed in the atmospheres of Jupiter, Saturn and one of its moons, Titan. The report, by an international team of astronomers led by Mark Swain at the Jet Propulsion Laboratory in California, appears in the journal Nature (vol 463, pp 637-639).
On Earth, atmospheric methane is generated by living organisms, but on Jupiter and other gas giants, methane is produced by light interacting with other chemicals in the atmosphere. The latest research will help astronomers distinguish between the two sources of methane in their search for extraterrestrial life.
Astronomers have detected more than 400 planets orbiting stars beyond our solar system. Studies of HD 189733b, a hot gas giant that is larger than Jupiter, have confirmed that its atmosphere contains sodium, carbon monoxide, carbon dioxide, water vapour and methane
In an accompanying article in Nature, Seth Redfield of the Van Vleck Observatory at Wesleyan University in Connecticut writes: "A number of other worlds, soon to be discovered, will be small and rocky like Earth, and will have atmospheres that we can detect. It is quite possible that, within our lifetimes, atmospheric studies of these extrasolar planets will provide the first evidence of biological life beyond Earth."
One of the world's leading planet hunters, Michael Mayor, believes scientists will detect the first truly Earth-like planet beyond the solar system later this year. Speaking at a conference on alien life at the Royal Society in London last week, Professor Mayor of Geneva University said Nasa's Kepler space telescope will be first to spot a second Earth elsewhere in the galaxy.
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