MOFFET FIELD - The most Earth-like planet ever discovered is circling a star 600 light years away, a key finding in an ongoing quest to learn if life exists beyond Earth, scientists said on Monday.
The planet, called Kepler-22b, joins a list of more than 500 planets found to orbit stars beyond our solar system. It is the smallest and the best positioned to have liquid water on its surface -- among the ingredients necessary for life on Earth.
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"We are homing in on the true Earth-sized, habitable planets," said San Jose State University astronomer Natalie Batalha, deputy science team lead for NASA's Kepler Space Telescope that discovered the star.
The telescope, which was launched three years ago, is staring at about 150,000 stars in the constellations Cygnus and Lyra, looking for faint and periodic dimming as any circling planets pass by, relative to Kepler's line of sight.
Results will be extrapolated to determine the percentage of stars in the Milky Way galaxy that harbor potentially habitable, Earth-size planets.
This is the first detection of a potentially habitable world orbiting a Sun-like star, scientists reported in findings to be published in The Astrophysical Journal.
Kepler-22b is 600 light years away. A light year is the distance light travels in a year, about 10 trillion km.
Planets about the same distance from their parent stars as Earth take
roughly a year to complete an orbit. Scientists want to see at least
three transits to be able to rule out other explanations for
fluctuations in a star's light, such as small companion stars. Results
also are verified by ground and other space telescopes.
Kepler-22b, which is about 2.4 times the radius of Earth, sits squarely
in its star's so-called "habitable zone," the region where liquid water
could exist on the surface. Follow-up studies are underway to determine
if the planet is solid, like Earth, or more gaseous like Neptune.
"We don't know anything about the planets between Earth-size and
Neptune-size because in our solar system we have no examples of such
planets. We don't know what fraction are going to be rocky, what
fraction are going to be water worlds, what fraction are ice worlds. We
have no idea until we measure one and see," Batalha said at a news
conference at NASA Ames Research Center in Moffet Field, California.
If Kepler-22b has a surface and a cushion of atmosphere similar to
Earth's, it would be about 22 degrees Celsius, about the same
as a spring day in Earth's temperate zone.
Among the 2,326 candidate planets found by the Kepler team, 10 are
roughly Earth-size and reside in their host stars' habitable zones.
Another team of privately funded astronomers is scanning the target
stars for non-naturally occurring radio signals, part of a project known
as SETI, or the Search for Extraterrestrial Intelligence.
"As soon as we find a different, a separate, an independent example of
life somewhere else, we're going to know that it's ubiquitous throughout
the universe," said astronomer Jill Tarter, director of the SETI
Institute in Mountain View.
The Kepler team is meeting for its first science conference this week.