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NASA’s Kepler mission has discovered 11 new planetary systems hosting
26 confirmed planets. These discoveries nearly double the number of
verified planets and triple the number of stars known to have more
than one planet that transits, or passes in front of, the star. Such
systems will help astronomers better understand how planets form.

The planets orbit close to their host stars and range in size from 1.5
times the radius of Earth to larger than Jupiter. Fifteen are between
Earth and Neptune in size. Further observations will be required to
determine which are rocky like Earth and which have thick gaseous
atmospheres like Neptune. The planets orbit their host star once every
six to 143 days. All are closer to their host star than Venus is to
our Sun.

“Prior to the Kepler mission, we knew of perhaps 500 exoplanets across
the whole sky,” said Doug Hudgins, Kepler program scientist at NASA
Headquarters in Washington. “Now, in just two years staring at a patch
of sky not much bigger than your fist, Kepler has discovered more than
60 planets and more than 2,300 planet candidates. This tells us that
our galaxy is positively loaded with planets of all sizes and orbits.”

Kepler identifies planet candidates by repeatedly measuring the change
in brightness of more than 150,000 stars to detect when a planet
passes in front of the star. That passage casts a small shadow toward
Earth and the Kepler spacecraft.

Each of the new confirmed planetary systems contains two to five
closely spaced transiting planets. In tightly packed planetary
systems, the gravitational pull of the planets on each other causes
some planets to accelerate and some to decelerate along their orbits.
The acceleration causes the orbital period of each planet to change.
Kepler detects this effect by measuring the changes, or so-called
Transit Timing Variations (TTVs).

Planetary systems with TTVs can be verified without requiring
extensive ground-based observations, accelerating confirmation of
planet candidates. The TTV detection technique also increases Kepler’s
ability to confirm planetary systems around fainter and more distant

Five of the systems (Kepler-25, Kepler-27, Kepler-30, Kepler-31 and
Kepler-33) contain a pair of planets where the inner planet orbits the
star twice during each orbit of the outer planet. Four of the systems
(Kepler-23, Kepler-24, Kepler-28 and Kepler-32) contain a pairing
where the outer planet circles the star twice for every three times
the inner planet orbits its star.

“These configurations help to amplify the gravitational interactions
between the planets, similar to how my sons kick their legs on a swing
at the right time to go higher,” said Jason Steffen, the Brinson
postdoctoral fellow at Fermilab Center for Particle Astrophysics in
Batavia, Ill., and lead author of a paper confirming four of the

Kepler-33, a star that is older and more massive than our Sun, had the
most planets. The system hosts five planets, ranging in size from 1.5
to 5 times that of Earth. All of the planets are located closer to
their star than any planet is to our Sun.

The properties of a star provide clues for planet detection. The
decrease in the star’s brightness and duration of a planet transit,
combined with the properties of its host star, present a recognizable
signature. When astronomers detect planet candidates that exhibit
similar signatures around the same star, the likelihood of any of
these planet candidates being a false positive is very low.

“The approach used to verify the Kepler-33 planets shows the overall
reliability is quite high,” said Jack Lissauer, planetary scientist at
NASA Ames Research Center at Moffett Field, Calif., and lead author of
the paper on Kepler-33. “This is a validation by multiplicity.”

These discoveries are published in four different papers in the
Astrophysical Journal and the Monthly Notices of the Royal
Astronomical Society.

IMAGE…..Kepler’s Planetary Systems, Jan. 2012
The artist’s rendering depicts the multiple planet systems discovered by NASA’s Kepler mission. Out of hundreds of candidate planetary systems, scientists had previously verified six systems with multiple transiting planets (denoted here in red). Now, Kepler observations have verified planets (shown here in green) in 11 new planetary systems. Many of these systems contain additional planet candidates that are yet to be verified (shown here in dark purple). For reference, the eight planets of the solar system are shown in blue.

Credit: NASA Ames/Jason Steffen, Fermilab Center for Particle Astrophysics

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