NASA's Hubble Space Telescope has made the first detection ever of an organic molecule in the atmosphere of a Jupiter-sized planet orbiting another star. This breakthrough 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 is a crucial stepping stone to eventually characterizing prebiotic molecules on planets where life could exist," said Mark Swain of NASA's Jet Propulsion Laboratory (JPL), Pasadena, Calif., who led the team that made the discovery. Swain is 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 (NICMOS).
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 1,700 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,"
said Swain.
Swain's co-authors on the paper include Gautam Vasisht of JPL and Giovanna
Tinetti of University College, London.
The Hubble Space Telescope is a project of international cooperation between
NASA and the European Space Agency (ESA) and is managed by NASA's Goddard
Space Flight Center (GSFC) in Greenbelt, Md. The Space Telescope Science
Institute (STScI) conducts Hubble science operations. The institute is
operated for NASA by the Association of Universities for Research in
Astronomy, Inc., Washington, D.C. JPL manages the Spitzer Space Telescope for
NASA. Scheduled for launch in 2013, JWST will probe even deeper into the
universe than Hubble can now. JWST is an international collaboration between
NASA, ESA, and the Canadian Space Agency (CSA). GSFC is managing the
development effort. The prime contractor is Northrop Grumman Space
Technologies. STScI will operate JWST after launch.
Credit: NASA/ESA/G. Bacon (STScI)
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