NASA's Kepler Discovery Confirms First Planet Orbiting Two Stars

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Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
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Michele Johnson
Ames Research Center, Moffett Field, Calif.
michele.johnson@nasa.gov

News release: 2011-292 Sept. 15, 2011

NASA's Kepler Discovery Confirms First Planet Orbiting Two Stars

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2011-292&cid=release_2011-292

PASADENA, Calif. – The existence of a world with a double sunset, as portrayed in the film
Star Wars more than 30 years ago, is now scientific fact. NASA's Kepler mission has made the
first unambiguous detection of a circumbinary planet -- a planet orbiting two stars -- 200 light-
years from Earth.

Unlike Star Wars' Tatooine, the planet is cold, gaseous and not thought to harbor life, but its
discovery demonstrates the diversity of planets in our galaxy. Previous research has hinted at the
existence of circumbinary planets, but clear confirmation proved elusive. Kepler detected such a
planet, known as Kepler-16b, by observing transits, where the brightness of a parent star dims
from the planet crossing in front of it.

"This discovery confirms a new class of planetary systems that could harbor life," Kepler
Principal Investigator William Borucki, of NASA's Ames Research Center in Moffett Field,
Calif., said. "Given that most stars in our galaxy are part of a binary system, this means the
opportunities for life are much broader than if planets form only around single stars. This
milestone discovery confirms a theory that scientists have had for decades but could not prove
until now."

A research team led by Laurance Doyle of the SETI Institute in Mountain View, Calif., used data
from the Kepler space telescope, which measures dips in the brightness of more than 150,000
stars, to search for transiting planets. Kepler is the first NASA mission capable of finding Earth-
size planets in or near the "habitable zone," the region in a planetary system where liquid water
can exist on the surface of the orbiting planet.

Scientists detected the new planet in the Kepler-16 system, a pair of orbiting stars that eclipse
each other from our vantage point on Earth. When the smaller star partially blocks the larger star,
a primary eclipse occurs, and a secondary eclipse occurs when the smaller star is occulted, or
completely blocked, by the larger star.

Astronomers further observed that the brightness of the system dipped even when the stars were
not eclipsing one another, hinting at a third body. The additional dimming in brightness events,
called the tertiary and quaternary eclipses, reappeared at irregular intervals of time, indicating the
stars were in different positions in their orbit each time the third body passed. This showed the
third body was circling, not just one, but both stars, in a wide circumbinary orbit.

The gravitational tug on the stars, measured by changes in their eclipse times, was a good
indicator of the mass of the third body. Only a very slight gravitational pull was detected, one
that only could be caused by a small mass. The findings are described in a new study published
Friday, Sept. 16, in the journal Science.

"Most of what we know about the sizes of stars comes from such eclipsing binary systems, and
most of what we know about the size of planets comes from transits," said Doyle, who also is the
lead author and a Kepler participating scientist. "Kepler-16 combines the best of both worlds,
with stellar eclipses and planetary transits in one system."

This discovery confirms that Kepler-16b is an inhospitable, cold world about the size of Saturn
and thought to be made up of about half rock and half gas. The parent stars are smaller than our
sun. One is 69 percent the mass of the sun and the other only 20 percent. Kepler-16b orbits
around both stars every 229 days, similar to Venus' 225-day orbit, but lies outside the system's
habitable zone, where liquid water could exist on the surface, because the stars are cooler than
our sun.

"Working in film, we often are tasked with creating something never before seen," said visual
effects supervisor John Knoll of Industrial Light & Magic, a division of Lucasfilm Ltd., in San
Francisco. "However, more often than not, scientific discoveries prove to be more spectacular
than anything we dare imagine. There is no doubt these discoveries influence and inspire
storytellers. Their very existence serves as cause to dream bigger and open our minds to new
possibilities beyond what we think we 'know.'"

For more information about the Kepler mission and to view the digital press kit, visit:
http://www.nasa.gov/kepler

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