Astronomers Detect
First Organic Molecule On An Exoplanet
(19 March 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
characterising 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.
The Hubble Space Telescope is a project of international
co-operation 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 conducts Hubble science operations. The institute is operated
for NASA by the Association of Universities for Research in Astronomy, Inc.,
Washington, DC. Scheduled for launch in 2013, the James Webb Space Telescope 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.
JPL manages the Spitzer Space Telescope mission for NASA's
Science Mission Directorate, Washington. Science operations are conducted at
the Spitzer Science Center at the California Institute of Technology, also in
Pasadena. Caltech manages JPL for NASA.
(source: NASA Jet Propulsion
Laboratory)
|
||||||||||||
