NASA's Kepler Mission Discovers two Planets Transiting Same Star

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Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
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Michael Mewhinney 650-604-3937
Ames Research Center, Moffett Field, Calif.
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J.D. Harrington 202-358-5241
NASA Headquarters, Washington
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News release: 2010-279 Aug. 26, 2010

NASA's Kepler Mission Discovers two Planets Transiting Same Star

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2010-279&cid=release_2010-279

Pasadena, Calif. -- NASA's Kepler spacecraft has discovered the first confirmed planetary
system with more than one planet crossing in front of, or transiting, the same star.

The transit signatures of two distinct planets were seen in the data for the sun-like star
designated Kepler-9. The planets were named Kepler-9b and 9c. The discovery incorporates
seven months of observations of more than 156,000 stars as part of an ongoing search for Earth-
sized planets outside our solar system. The findings will be published in this week's issue of the
journal Science.

Kepler's ultra-precise camera measures tiny decreases in stars' brightness that occur when a planet
transits them. The size of the planet can be derived from these temporary dips.

The distance of the planet from a star can be calculated by measuring the time between
successive dips as the planet orbits the star. Small variations in the regularity of these dips can be
used to determine the masses of planets and detect other non-transiting planets in the system.

In June 2010, Kepler mission scientists submitted findings for peer review that identified more
than 700 planet candidates in the first 43 days of Kepler data. The data included five additional
candidate systems that appear to exhibit more than one transiting planet. The Kepler team
recently identified a sixth target exhibiting multiple transits and accumulated enough followup
data to confirm this multi-planet system.

"Kepler's high-quality data and round-the-clock coverage of transiting objects enable a whole
host of unique measurements to be made of the parent stars and their planetary systems," said
Doug Hudgins, the Kepler program scientist at NASA Headquarters in Washington.

Scientists refined the estimates of the masses of the planets using observations from the W.M.
Keck Observatory in Hawaii. The observations show Kepler-9b is the larger of the two planets,
and both have masses similar to but less than Saturn. Kepler-9b lies closest to the star, with an
orbit of about 19 days, while Kepler-9c has an orbit of about 38 days. By observing several
transits by each planet over the seven months of data, the time between successive transits could
be analyzed.

"This discovery is the first clear detection of significant changes in the intervals from one
planetary transit to the next, what we call transit timing variations," said Matthew Holman, a
Kepler mission scientist from the Harvard-Smithsonian Center for Astrophysics in Cambridge,
Mass. "This is evidence of the gravitational interaction between the two planets as seen by the
Kepler spacecraft."

In addition to the two confirmed giant planets, Kepler scientists also have identified what
appears to be a third, much smaller transit signature in the observations of Kepler-9. That
signature is consistent with the transits of a super-Earth-sized planet about 1.5 times the radius of
Earth in a scorching, near-sun 1.6 day-orbit. Additional observations are required to determine
whether this signal is indeed a planet or an astronomical phenomenon that mimics the appearance
of a transit.

NASA's Ames Research Center in Moffett Field, Calif., manages Kepler's ground system
development, mission operations and science data analysis. NASA's Jet Propulsion Laboratory in
Pasadena, Calif., managed Kepler mission development. Ball Aerospace and 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 the Kepler science
data.

For graphics, including new animations, visit http://www.nasa.gov/kepler .

More information about exoplanets and NASA's planet-finding program is at
http://planetquest.jpl.nasa.gov .

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