J.D. Harrington
Headquarters, Washington
202-358-5241
j.d.harrington@nasa.gov
Michele Johnson
Ames Research Center, Moffett Field,
Calif.
650-604-4789
michele.johnson@nasa.gov
NASA's Kepler mission has discovered
multiple transiting planets orbiting two suns for the first time. The system,
known as a circumbinary planetary system, is 4,900 light-years from Earth in
the constellation Cygnus.
Coming less than a year after the
announcement of the first circumbinary planet, Kepler-16b, this discovery
proves that more than one planet can form and persist in the stressful realm of
a binary star. The discovery demonstrates the diversity of planetary systems in
our galaxy.
Astronomers detected two planets in the
Kepler-47 system, a pair of orbiting stars that eclipse each other every 7.5
days from our vantage point on Earth. One star is similar to the sun in size,
but only 84 percent as bright. The second star is diminutive, measuring only
one-third the size of the sun and less than 1 percent as bright.
"In contrast to a single planet
orbiting a single star, the planet in a circumbinary system must transit a
'moving target.' As a consequence, time intervals between the transits and
their durations can vary substantially, sometimes short, other times
long," said Jerome Orosz, associate professor of astronomy at San Diego
State University and lead author of the paper. "The intervals were the
telltale sign these planets are in circumbinary orbits."
The inner planet, Kepler-47b, orbits the
pair of stars in less than 50 days. While it cannot be directly viewed, it is
thought to be a sweltering world, where the destruction of methane in its
super-heated atmosphere might lead to a thick haze that could blanket the
planet. At three times the radius of Earth, Kepler-47b is the smallest known
transiting circumbinary planet.
The outer planet, Kepler-47c, orbits its
host pair every 303 days, placing it in the so-called "habitable
zone," the region in a planetary system where liquid water might exist on
the surface of a planet. While not a world hospitable for life, Kepler-47c is
thought to be a gaseous giant slightly larger than Neptune, where an atmosphere
of thick bright water-vapor clouds might exist.
"Unlike our sun, many stars are
part of multiple-star systems where two or more stars orbit one another. The
question always has been -- do they have planets and planetary systems? This
Kepler discovery proves that they do," said William Borucki, Kepler
mission principal investigator at NASA's Ames Research Center in Moffett Field,
Calif. "In our search for habitable planets, we have found more opportunities
for life to exist."
To search for transiting planets, the
research team used data from the Kepler space telescope, which measures dips in
the brightness of more than 150,000 stars. Additional ground-based
spectroscopic observations using telescopes at the McDonald Observatory at the
University of Texas at Austin helped characterize the stellar properties. The
findings are published in the journal Science.
"The presence of a full-fledged
circumbinary planetary system orbiting Kepler-47 is an amazing discovery,"
said Greg Laughlin, professor of Astrophysics and Planetary Science at the
University of California in Santa Cruz. "These planets are very difficult
to form using the currently accepted paradigm, and I believe that theorists,
myself included, will be going back to the drawing board to try to improve our
understanding of how planets are assembled in dusty circumbinary disks."
Ames manages Kepler's ground system
development, mission operations and science data analysis. NASA's Jet Propulsion
Laboratory in Pasadena, Calif., managed the Kepler mission development.
Ball Aerospace & Technologies Corp.
in Boulder, Colo., developed the Kepler flight system and supports mission
operations with the Laboratory for Atmospheric and Space Physics at the
University of Colorado in Boulder.
The Space Telescope Science Institute in
Baltimore archives, hosts and distributes Kepler science data. Kepler is NASA's
tenth Discovery Mission and funded by NASA's Science Mission Directorate at the
agency's headquarters in Washington.
For more information about the Kepler
mission, visit http://www.nasa.gov/kepler.
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