In a first for astronomy, methane is spotted on distant planet

AFP - Thursday, March 20

PARIS (AFP) - - Astronomers on Wednesday announced they had detected methane in the atmosphere of a planet 63 light years away, boosting prospects for identifying any life that exists beyond our Solar System.

The team also confirmed previous suspicions that the planet, known by the tag of HD 189733b, has water in its atmosphere.

Reporting their work in the weekly British journal Nature, astronomers from NASA's Jet Propulsion Laboratory (JPL) used the orbiting US-European Hubble telescope to get an infrared spectroscopic signature of the planet's atmosphere.

Spectroscopy entails breaking light into its components to reveal the "fingerprints" of chemicals it contains.

They found an unmistakeable signature for methane, a molecule of carbon and hydrogen that can in some conditions play a key role in creating the conditions for life.

In this case, life on HD 189733b is almost certainly out of the question.

The planet, located in the constellation of Vulpecula, or the Little Fox, is one of a type of large planets called "hot Jupiters," whose surface is scorched and where liquid water could not exist.

HD 189733b is closer to its star than Mercury is to the Sun. It takes only two days to complete one orbit and has a sweltering temperature of 900 degrees Celsius (1,650 degrees Fahrenheit) -- hot enough to melt silver.

What counts, though, is the achievement of spotting the methane.

The technique could be extended to other planets that orbit cooler stars in the so-called "Goldilocks Zone," where the temperature is not too hot, not too cold but just right for nurturing life.

"This is a crucial stepping stone to eventually characterising pre-biotic molecules on planets where life could exists," said JPL's Mark Swain, who led the investigation.

"This observation is proof that spectroscopy can eventually be done on a cooler and potentially habitable Earth-sized planet orbiting a dimmer red dwarf-type star."

More than 270 planets beyond our Solar System, known as exoplanets, have been spotted since the first one was detected 13 years ago.

Although the tally of planets is steadily rising, the big frustration has been to garner details about their chemical composition -- the key to identifying whether any holds the potential for life.

Swain's team used the powerful NICMOS spectroscopy camera aboard the Hubble to get snapshots as HD 189733b passed on a direct line between its own star and Earth on a day in May last year.

The light from the star passed through the planet's atmosphere, bringing with it telltale chemical signatures -- but the chief task lay in finding these needles in a haystack of wavelengths.

The observations also confirmed the existence of water molecules, something that had been inferred earlier by NASA's Spitzer space telescope.

In a commentary, University of Arizona planetary scientist Adam Showman said that the achievement was a remarkable step forward in exoplanet knowledge.

The Hubble and Spitzer telescopes are now entering old age, but new-generation, more powerful orbital platforms are under development, he noted.

"We are thus now seeing but the opening salvo in a revolution that will extend humankind's view of planetary worlds far beyond the provincial boundaries of our Solar System," said Showman, writing in Nature.

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