Smallest extrasolar planet: A rocky world 1.4 x Earth’s size

I’m excited by this news release, especially as it connects to my “Cool Science” book, Astrobiology and my school visit talk and upcoming book Our Next Planet.

January 10, 2011

Trent J. Perrotto
Headquarters, Washington
+1 202-358-0321
[email protected]

Rachel Hoover
Ames Research Center, Moffett Field, Calif.
+1 650-604-0643
[email protected]


NASA’s Kepler mission confirmed the discovery of its first rocky
planet, named Kepler-10b. Measuring 1.4 times the size of Earth, it is
the smallest planet ever discovered outside our solar system.

The discovery of this so-called exoplanet is based on more than eight
months of data collected by the spacecraft from May 2009 to early
January 2010.

“All of Kepler’s best capabilities have converged to yield the first
solid evidence of a rocky planet orbiting a star other than our sun,”
said Natalie Batalha, Kepler’s deputy science team lead at NASA’s Ames
Research Center in Moffett Field, Calif., and primary author of a
paper on the discovery accepted by the Astrophysical Journal. “The
Kepler team made a commitment in 2010 about finding the telltale
signatures of small planets in the data, and it’s beginning to pay

Kepler’s ultra-precise photometer measures the tiny decrease in a
star’s brightness that occurs when a planet crosses in front of it.
The size of the planet can be derived from these periodic dips in
brightness. The distance between the planet and the star is calculated
by measuring the time between successive dips as the planet orbits the

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 planet’s surface. However, since it
orbits once every 0.84 days, Kepler-10b is more than 20 times closer
to its star than Mercury is to our sun and not in the habitable zone.

Kepler-10 was the first star identified that could potentially harbor
a small transiting planet, placing it at the top of the list for
ground-based observations with the W.M. Keck Observatory 10-meter
telescope in Hawaii.

Scientists waiting for a signal to confirm Kepler-10b as a planet were
not disappointed. Keck was able to measure tiny changes in the star’s
spectrum, called Doppler shifts, caused by the telltale tug exerted by
the orbiting planet on the star.

“The discovery of Kepler 10-b is a significant milestone in the search
for planets similar to our own,” said Douglas Hudgins, Kepler program
scientist at NASA Headquarters in Washington. “Although this planet is
not in the habitable zone, the exciting find showcases the kinds of
discoveries made possible by the mission and the promise of many more
to come,” he said.

Knowledge of the planet is only as good as the knowledge of the star
it orbits. Because Kepler-10 is one of the brighter stars being
targeted by Kepler, scientists were able to detect high frequency
variations in the star’s brightness generated by stellar oscillations,
or starquakes. This analysis allowed scientists to pin down
Kepler-10b’s properties.

There is a clear signal in the data arising from light waves that
travel within the interior of the star. Kepler Asteroseismic Science
Consortium scientists use the information to better understand the
star, just as earthquakes are used to learn about Earth’s interior
structure. As a result of this analysis, Kepler-10 is one of the most
well characterized planet-hosting stars in the universe.

That’s good news for the team studying Kepler-10b. Accurate stellar
properties yield accurate planet properties. In the case of
Kepler-10b, the picture that emerges is of a rocky planet with a mass
4.6 times that of Earth and with an average density of 8.8 grams per
cubic centimeter — similar to that of an iron dumbbell.

# # #

Ames 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.

Kepler is NASA’s 10th Discovery Mission and is funded by NASA’s
Science Mission Directorate at the agency’s headquarters.

More information about the Kepler mission: