Hubble Telescope Finds Methane On Jupiter-Sized World
A team of astronomers led by Mark
Swain of NASA's Jet Propulsion Laboratory in Pasadena, CA, has made
the first detection ever of an organic molecule in the atmosphere
of a Jupiter-sized planet orbiting another star. The breakthrough,
made with NASA's Hubble Space Telescope, is an important step in
eventually identifying signs of life on a planet outside our solar
system.
The molecule found by Hubble is methane, which under the right
circumstances can play a key role in prebiotic chemistry -- the
chemical reactions considered necessary to form life as we know
it.
This discovery proves that Hubble and upcoming space missions,
such as NASA's James Webb Space Telescope, can detect organic
molecules on planets around other stars by using spectroscopy,
which splits light into its components to reveal the "fingerprints"
of various chemicals. "This is a crucial stepping stone to
eventually characterizing prebiotic molecules on planets where life
could exist," said Swain, lead author of a paper appearing in the
March 20 issue of Nature.
The discovery comes after extensive observations made in May
2007 with Hubble's Near Infrared Camera and Multi-Object
Spectrometer. It also confirms the existence of water molecules in
the planet's atmosphere, a discovery made originally by NASA's
Spitzer Space Telescope in 2007.
"With this observation there is no question whether there is
water or not -- water is present," said Swain.
The planet now known to have methane and water is located 63
light-years away in the constellation Vulpecula. Called HD 189733b,
the planet is so massive and so hot it is considered an unlikely
host for life. HD 189733b, dubbed a "hot Jupiter," is so close to
its parent star it takes just over two days to complete an orbit.
These objects are the size of Jupiter but orbit closer to their
stars than the tiny innermost planet Mercury in our solar system.
HD 189733b's atmosphere swelters at 1700 degrees Fahrenheit, about
the same temperature as the melting point of silver.
Though the star-hugger planet is too hot for life as we know
it, "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," Swain said. 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.
The observations were made as the planet HD 189733b passed in
front of its parent star in what astronomers call a transit. 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 the star HD 189733. The
astronomers were surprised to find that the planet has more methane
than predicted by conventional models for "hot Jupiters."
"This indicates we don't really understand exoplanet atmospheres
yet," said Swain. "These measurements are an important step to our
ultimate goal of determining the conditions, such as temperature,
pressure, winds, clouds, etc., and the chemistry on planets where
life could exist. Infrared spectroscopy is really the key to these
studies because it is best matched to detecting molecules."