One Star Boasts A Solar System Of At Least Six-Planets
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."
Kepler Telescope During Assembly NASA Image
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, CA, 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.
Artists Concept Of Exoplanet NASA Image
"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.