NASA's Kepler Confirms First Planet In Habitable Zone Of
Sun-Like Star
NASA's Kepler mission has confirmed its first planet in the
"habitable zone," the region where liquid water could exist on a
planet's surface. Kepler also has discovered more than 1,000 new
planet candidates, nearly doubling its previously known count. Ten
of these candidates are near-Earth-size and orbit in the habitable
zone of their host star. Candidates require follow-up observations
to verify they are actual planets.
Kepler-22b NASA Image
The newly confirmed planet, Kepler-22b, is the smallest yet
found to orbit in the middle of the habitable zone of a star
similar to our sun. The planet is about 2.4 times the radius of
Earth. Scientists don't yet know if Kepler-22b has a predominantly
rocky, gaseous or liquid composition, but its discovery is a step
closer to finding Earth-like planets. Previous research hinted at
the existence of near-Earth-size planets in habitable zones, but
clear confirmation proved elusive. Two other small planets orbiting
stars smaller and cooler than our sun recently were confirmed on
the very edges of the habitable zone, with orbits more closely
resembling those of Venus and Mars.
"This is a major milestone on the road to finding Earth's twin,"
said Douglas Hudgins, Kepler program scientist at NASA Headquarters
in Washington. "Kepler's results continue to demonstrate the
importance of NASA's science missions, which aim to answer some of
the biggest questions about our place in the universe."
Kepler discovers planets and planet candidates by measuring dips
in the brightness of more than 150,000 stars to search for planets
that cross in front, or "transit," the stars. Kepler requires at
least three transits to verify a signal as a planet. "Fortune
smiled upon us with the detection of this planet," said William
Borucki, Kepler principal investigator at NASA Ames Research Center
at Moffett Field, Calif., who led the team that discovered
Kepler-22b. "The first transit was captured just three days after
we declared the spacecraft operationally ready. We witnessed the
defining third transit over the 2010 holiday season."
The Kepler science team uses ground-based telescopes and the
Spitzer Space Telescope to review observations on planet candidates
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.
Kepler-22b is located 600 light-years away. While the planet is
larger than Earth, its orbit of 290 days around a sun-like star
resembles that of our world. The planet's host star belongs to the
same class as our sun, called G-type, although it is slightly
smaller and cooler. Of the 54 habitable zone planet candidates
reported in February 2011, Kepler-22b is the first to be confirmed.
This milestone will be published in The Astrophysical Journal.
Kepler Spacecraft
The Kepler team is hosting its inaugural science conference at
Ames Dec. 5-9, announcing 1,094 new planet candidate discoveries.
Since the last catalog was released in February, the number of
planet candidates identified by Kepler has increased by 89 percent
and now totals 2,326. Of these, 207 are approximately Earth-size,
680 are super Earth-size, 1,181 are Neptune-size, 203 are
Jupiter-size and 55 are larger than Jupiter. The findings, based on
observations conducted May 2009 to September 2010, show a dramatic
increase in the numbers of smaller-size planet candidates.
Kepler observed many large planets in small orbits early in its
mission, which were reflected in the February data release. Having
had more time to observe three transits of planets with longer
orbital periods, the new data suggest that planets one to four
times the size of Earth may be abundant in the galaxy. The number
of Earth-size and super Earth-size candidates has increased by more
than 200 and 140 percent since February, respectively.
There are 48 planet candidates in their star's habitable zone.
While this is a decrease from the 54 reported in February, the
Kepler team has applied a stricter definition of what constitutes a
habitable zone in the new catalog, to account for the warming
effect of atmospheres, which would move the zone away from the
star, out to longer orbital periods. "The tremendous growth in the
number of Earth-size candidates tells us that we're honing in on
the planets Kepler was designed to detect: those that are not only
Earth-size, but also are potentially habitable," said Natalie
Batalha, Kepler deputy science team lead at San Jose State
University in California. "The more data we collect, the keener our
eye for finding the smallest planets out at longer orbital
periods."