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Astronomers Detect First Organic Molecule on an Exoplanet
March 19, 2008
A team of astronomers led by Mark Swain of NASA's Jet Propulsion Laboratory, Pasadena, Calif., 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," said Swain.
More information on the discovery and artist's concepts are online at: hubblesite.org...
. 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 and is managed by NASA's Goddard
Space Flight Center in Greenbelt, Md. The Space Telescope Science Institute