Scientists have detected the presence of an organic molecule in the atmosphere of an extrasolar planet for the first time, NASA announced today.
The finding, detailed in the March 20 issue of the journal Nature, marks a breakthrough in the attempt to detect signs of life on planets beyond our solar system.
The tell-tale signature of the molecule methane in the atmosphere of the Jupiter-sized planet HD 189733b was made by the Hubble Space Telescope's Near Infrared Camera and Multi-Object Spectrometer (NICMOS) in May 2007.
MIT's Sara Seager, who was not involved with the study, said that she is "cautiously optimistic that the methane detection is robust" at a press conference announcing the finding.
It is thought that under the right circumstances, methane can play a key role in prebiotic chemistry, or the chemical reactions considered necessary to produce life as we know it on Earth.
So the Hubble observations of HD 189733b, which is likely too hot to support life, "is a dress rehearsal for future searches for life on more hospitable planets," said study team member Mark Swain of NASA's Jet Propulsion Laboratory in California.
Methane, composed of carbon and hydrogen, has been detected on most planets in our solar system, but never before on a world orbiting another star.
On a smaller, more hospitable planet, methane could be indicative of biological activity, though methane can be produced by non-biological processes. Methane generally breaks up quickly in Earth's atmosphere through chemical reactions; this same process could occur on other small planets. And on a small planet, the hydrogen from the broken-up methane would likely escape quickly to space. So if a high amount of methane is detected on an Earth-sized planet, it could be the result of biological processes, because non-biological processes tend not to produce large amounts of the molecule. Astronomers plan to use the James Webb Telescope to search for water and methane on other extrasolar planets.
On Earth, methane is one of the main components of natural gas and is produced by termites, wetland environments, waste landfills and even livestock.
It is unlikely that HD 189733b, located 63 light-years away in the constellation Vulpecula, harbors life. Although about the size of Jupiter, the planet orbits closer to its star than the innermost planet in our solar system, Mercury. This close proximity to its sun means the planet's atmosphere swelters at a temperature of about 900 degrees Celsius, the melting point of silver.
"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!" said researcher Giovanna Tinetti of the University College London and the European Space Agency.
The NICMOS observations also confirmed the presence of water molecules in the planet's atmosphere, originally detected by NASA's Spitzer Space Telescope in 2007.