Methane found on extrasolar planet
BY EMILY BALDWIN
ASTRONOMY NOW
Posted: March 20, 2008

The Hubble Space Telescope has made the first ever detection of an organic molecule on a planet orbiting another star, an important breakthrough in identifying signs of life on a planet outside our Solar System.

HD 189733b is located 63 light years away in the constellation Vulpecula and resides so close to its parent star that it completes an orbit in just over two days, placing it into the category of ‘hot-jupiters’. The observations were made as the planet made a transit in front of its parent star. As the light from the star passed briefly through the atmosphere along the edge of the planet, the gases in the atmosphere imprinted their unique signatures on the starlight from HD 189733, a light-splitting technique known as spectroscopy. Both water vapour and methane are now known to exist on the planet. Water molecules were first detected by the Spitzer Space Telescope in 2007, and confirmed with these new observations. "Water alone could not explain all the spectral features observed,” says Giovanna Tinetti from University College London and the European Space Agency. “The additional contribution of methane is necessary to fit the Hubble data".

Artist impression of the extrasolar planet HD 189733b orbiting its parent star, now known to have methane and water vapour in its atmosphere. Image: ESA/NASA/G. Tinetti (UCL/ESA).

Under the right circumstances methane can play a pivotal role in prebiotic chemistry — the chemical reactions considered necessary to produce the life we are familiar with on Earth. Methane is produced from a variety of natural and manmade sources on the Earth, such as livestock, waste landfills or as a by-product of energy generation. However, the researchers are quick to rule out any biological origin of the methane found on HD 189733b because the planet’s atmosphere is far too hot, at a sweltering 900 degrees Celsius, for even the hardiest life forms to survive.

Although methane has been detected on most of the planets in our Solar System, this is the first time that any organic molecule has been detected on a world orbiting another star. The new discovery proves that Hubble and upcoming space missions, such as the NASA/ESA/CSA James Webb Space Telescope, can detect organic molecules on planets around other stars using spectroscopy. "This is a crucial stepping stone to eventually characterising prebiotic molecules on planets where life could exist", says Mark Swain of NASA's Jet Propulsion Laboratory, who led the research. "These measurements are an important step to our ultimate goal of determining the conditions, such as temperature, pressure, winds, clouds and the chemistry on planets where life could exist.”

The ultimate goal of studies like these is to identify prebiotic molecules in the atmospheres of planets in the ‘habitable zones’ around other stars, where temperatures are right for
water to remain liquid rather than freeze or evaporate away.

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