Marker of life detected on distant exoplanet

TORONTO: For the first time methane gas has been detected on a planet outside our Solar System. The organic molecule is a key product of life on Earth, and might be a useful tool for finding it elsewhere, say experts.

Using the Hubble Space Telescope astronomers were able to detect a small amount of methane and water vapour in the upper atmosphere of the planet named HD 189733b.

The hot 'Jupiter-like' planet is 60 light-years away in the constellation Vulpecula. The planet is a little heavier than our largest planets, orbits closer than Venus, and was ideal for research because it orbits its sun in only 2.2 Earth days.

Alien-hunt test run

"This is a dress rehearsal for future searches for life on other planets," said Mark Swain, an astronomer with the California Institute of Technology in Pasadena, and lead author of a study detailing the discovery in the U.K. journal Nature today.

"If we could detect methane on a more hospitable planet, that would be really exciting, and we look forward to doing that in the future," he said, noting that HD 189733b is likely too hot for life.

The methane and water vapour were observed using a technique where astronomers watch the planet pass in front of the star and capture the small amount of starlight passing through the planet's atmosphere.

Methane is more than just a good marker of life, though. It may have also played an important role in the genesis of life because in certain circumstances it combines with other common molecules to produce amino acids, the building blocks of proteins.

The discovery of methane on this particular exoplanet was unexpected because the atmosphere has a temperature of around 727 ºC. At that heat, methane breaks down into carbon monoxide here on Earth. However, the experts believe that the night-time side of the planet is cooler and richer in methane, while the sweltering hot daytime side contains most of the unobserved carbon monoxide.

Cautiously optimistic

"We are cautiously optimistic that the methane detection is robust," commented Sarah Seager, an exoplanet astronomer with the Massachusetts Institute for Technology in Boston, Massachusetts, "but we would like to see this observation reproduced.

"It's amazing to be able to detect molecules in [an exoplanet's] atmosphere at all," added Seager who is not one of the study's authors.

This technique to capture light passing through the atmospheres of exoplanets will be used even more by future space telescopes, such as Hubble's replacement, NASA's James Webb Space Telescope, or the Kepler Space Telescope (set for launch in February 2009) allowing us to study exoplanets in much greater detail.

"Webb will be fantastic for this type of work," said Swain. "It's not only bigger, and collecting more photons is always an advantage in astronomy, but it will also be orbiting Earth in a different type of orbit that is more stable. These types of observations are more about precision than sensitivity."

Cosmos Online / by Graeme Stemp-Morlock