Scientists spot organic molecule on distant planet

WASHINGTON (Reuters) - An organic molecule has been spotted for the first time in the atmosphere of a planet outside our solar system, a key step toward possibly finding signs of life on a distant world, scientists said.

Astronomers using the Hubble Space Telescope found methane in the atmosphere of a planet called HD 189733b, which is about the size of Jupiter and is 63 light-years from Earth, they said in research published on Wednesday in the journal Nature.

Organic molecules contain carbon-hydrogen bonds and can be found in living things. Methane, for instance, is found in natural gas and cattle belches.

But the scientists were quick to point out that this distant planet -- with atmospheric temperatures around 1,800 degrees Fahrenheit (1,000 degrees Celsius) -- is not thought to be a candidate for hosting any form of life.

"For this specific planet we observed, methane cannot be produced biologically," Giovanna Tinetti of the University College London, one of the researchers, said by e-mail.

"It's highly unlikely that cows could survive here," Tinetti joked.

"The idea is to repeat the same kind of observations in the future for planets which are less hostile to the development and evolution of life," she added.

HD 189733b is one of more than 270 planets to be discovered orbiting stars other than our sun -- called extrasolar planets. It is a "hot Jupiter" type, similar to the gas giant Jupiter in our solar system but reaching scorching temperatures because they orbit so closely to their stars.

This one whizzes around its star roughly every two Earth days.

Methane, composed of carbon and hydrogen, has been detected on many of the planets in our solar system.

"Under the right conditions, methane can contribute to the formation of amino acids," an important building block of life, said another member of the research group, Mark Swain of NASA's Jet Propulsion Laboratory in Pasadena, California.

The scientists were able to confirm the previously reported discovery of water molecules in the planet's atmosphere.

They made their observations as the planet passed in front of its parent star in what is called a transit. The scientists used a method called transit spectroscopy -- breaking light up into its various colors.

"You can think of the prism making a rainbow spectrum when you shine light through it. And we do this when the planet passes in front of its parent star. So what we see is the starlight filtered through the planet's atmosphere. The molecules in the atmosphere of the planet leave a fingerprint in the spectrum," Swain said in a telephone interview.

Separately, other astronomers used NASA's Spitzer Space Telescope and the Keck II Telescope in Hawaii to find water molecules in disks of dust and gas around two young stars.

The water is at the center of spinning disks of particles that may eventually coalesce to form planets around the stars DR Tau, 457 light-years from Earth and AS 205A, 391 light-years from Earth, they reported in Astrophysical Journal Letters.

(Editing by Maggie Fox and Eric Walsh)