NASA Finds Earth-Size Planet Candidates In Habitable Zone, Six Planet System
WASHINGTON -- NASA's Kepler mission has discovered its first
Earth-size planet candidates and its first candidates in the
habitable zone, a region where liquid water could exist on a planet's
surface. Five of the potential planets are near Earth-size and orbit
in the habitable zone of smaller, cooler stars than our sun.
Candidates require follow-up observations to verify they are actual
planets. Kepler also found six confirmed planets orbiting a sun-like
star, Kepler-11. This is the largest group of transiting planets
orbiting a single star yet discovered outside our solar system.
"In one generation we have gone from extraterrestrial planets being a
mainstay of science fiction, to the present, where Kepler has helped
turn science fiction into today's reality," said NASA Administrator
Charles Bolden. "These discoveries underscore the importance of
NASA's science missions, which consistently increase understanding of
our place in the cosmos."
The discoveries are part of several hundred new planet candidates
identified in new Kepler mission science data, released on Tuesday,
Feb. 1. The findings increase the number of planet candidates
identified by Kepler to-date to 1,235. Of these, 68 are approximately
Earth-size; 288 are super-Earth-size; 662 are Neptune-size; 165 are
the size of Jupiter and 19 are larger than Jupiter.
Of the 54 new planet candidates found in the habitable zone, five are
near Earth-sized. The remaining 49 habitable zone candidates range
from super-Earth size -- up to twice the size of Earth -- to larger
than Jupiter.
The findings are based on the results of observations conducted May 12
to Sept. 17, 2009, of more than 156,000 stars in Kepler's field of
view, which covers approximately 1/400 of the sky.
"The fact that we've found so many planet candidates in such a tiny
fraction of the sky suggests there are countless planets orbiting
sun-like stars in our galaxy," said William Borucki of NASA's Ames
Research Center in Moffett Field, Calif., the mission's science
principal investigator. "We went from zero to 68 Earth-sized planet
candidates and zero to 54 candidates in the habitable zone, some of
which could have moons with liquid water."
Among the stars with planetary candidates, 170 show evidence of
multiple planetary candidates. Kepler-11, located approximately 2,000
light years from Earth, is the most tightly packed planetary system
yet discovered. All six of its confirmed planets have orbits smaller
than Venus, and five of the six have orbits smaller than Mercury's.
The only other star with more than one confirmed transiting planet is
Kepler-9, which has three. The Kepler-11 findings will be published
in the Feb. 3 issue of the journal Nature.
"Kepler-11 is a remarkable system whose architecture and dynamics
provide clues about its formation," said Jack Lissauer, a planetary
scientist and Kepler science team member at Ames. "These six planets
are mixtures of rock and gases, possibly including water. The rocky
material accounts for most of the planets' mass, while the gas takes
up most of their volume. By measuring the sizes and masses of the
five inner planets, we determined they are among the lowest mass
confirmed planets beyond our solar system."
All of the planets orbiting Kepler-11 are larger than Earth, with the
largest ones being comparable in size to Uranus and Neptune. The
innermost planet, Kepler-11b, is ten times closer to its star than
Earth is to the sun. Moving outward, the other planets are
Kepler-11c, Kepler-11d, Kepler-11e, Kepler-11f, and the outermost
planet, Kepler-11g, which is half as far from its star as Earth is
from the sun.
The planets Kepler-11d, Kepler-11e and Kepler-11f have a significant
amount of light gas, which indicates that they formed within a few
million years of the system's formation.
"The historic milestones Kepler makes with each new discovery will
determine the course of every exoplanet mission to follow," said
Douglas Hudgins, Kepler program scientist at NASA Headquarters in
Washington.
Kepler, a space telescope, looks for planet signatures by measuring
tiny decreases in the brightness of stars caused by planets crossing
in front of them. This is known as a transit.
Since transits of planets in the habitable zone of sun-like stars
occur about once a year and require three transits for verification,
it is expected to take three years to locate and verify Earth-size
planets orbiting sun-like stars.
The Kepler science team uses ground-based telescopes and the Spitzer
Space Telescope to review observations on planetary candidates and
other objects of interest the spacecraft finds.
The star field that Kepler observes in the constellations Cygnus and
Lyra can only be seen from ground-based observatories in spring
through early fall. The data from these other observations help
determine which candidates can be validated as planets.
For more information about the Kepler mission, visit:
http://www.nasa.gov/kepler
Source: NASA
