|This undated handout artist rendering provided by NASA shows Kepler-22b, a planet known to comfortably circle in the habitable zone of a sun-like star. It is the first planet that NASA's Kepler mission has confirmed to orbit in a star's habitable zone -- the region around a star where liquid water, a requirement for life on Earth, could persist. NASA has found the new planet outside our solar system that's eerily similar to Earth in key aspects. Scientists say the temperature on the surface of the planet is about a comfy 72 degrees. Its star could almost be a twin of our sun. It likely has water and land. (AP Photo/NASA/Ames/JPL-Caltech)|
WASHINGTON (AP) - A newly discovered planet is eerily
similar to Earth and is sitting outside our solar system in what seems to be
the ideal place for life, except for one hitch. It's a bit too big.
The planet is smack in the middle of what astronomers
call the Goldilocks zone, that hard to find
place that's not too hot, not too cold, where water, which is essential for
life, doesn't freeze or boil. And it has a shopping mall-like surface
temperature of near 72 degrees, scientists say.
The planet's confirmation was announced Monday by NASA
along with other discoveries by its Kepler telescope, which was launched on a
planet-hunting mission in 2009.
That's the first planet confirmed in the habitable
zone for Kepler, which had already found Earth-like rocky planets elsewhere.
Twice before astronomers have announced a planet found in that zone, but
neither have been as promising.
"This is a phenomenal discovery in the course of
human history," Geoff Marcy of University of California, Berkeley, one of
the pioneers of planet-hunting outside our solar system, said in an email.
"This discovery shows that we Homo sapiens are straining our reach into
the universe to find planets that remind us of home. We are almost there."
The new planet - named Kepler-22b - has key aspects it
shares with Earth. It circles a star that could be the twin of our sun and at
just about the same distance. The planet's year of 290 days is even close to ours.
It likely has water and rock.
The only trouble is the planet's a bit big for life to
exist on the surface. The planet is about 2.4 times the size of Earth. It could
be more like the gas-and-liquid Neptune with only a rocky core and mostly
|Eight days after its encounter with Earth, the Galileo spacecraft captured this view of the moon in orbit around Earth. It was taken from a distance of about 3.9 million miles on December 16, 1992. Contrast and color have been computer enhanced to improve visibility by the Jet Propulsion Laboratory, who released the photo in Pasadena, California. (AP photo)|
"It's so exciting to imagine the
possibilities," said Natalie Batalha, the Kepler deputy science chief.
Floating on that "world completely covered in
water" could be like being on an Earth ocean and "it's not beyond the
realm of possibility that life could exist in such an ocean," Batalha said
in a phone interview.
Kepler can't find life itself, just where the
conditions might be right for it to thrive. And when astronomers look for life
elsewhere they're talking about everything ranging from microbes to advanced
intelligence that can be looking back at us.
So far the Kepler telescope has spotted 2,326
candidate planets outside our solar system with 139 of them potentially
habitable ones. Even though the confirmed Kepler-22b is a bit big, it is still
smaller than most of the other candidates. It is closest to Earth in size,
temperature and star than either of the two previously announced planets in the
The confirmation of one of two, though, has been
disputed. The latest discovery has been confirmed several ways, including by
two other telescopes.
Earlier this year, a European team of astronomers said
they had confirmed another planet in the habitable zone, but that one was hot
and barely on the inside edge of the habitable zone.
For Marcy, who is on the Kepler team, the newest
planet is a smidgen too large. But, "that smidgen makes all the
difference," he said.
Because its size implies that it's closer to Neptune
in composition than Earth, "I would bet my telescope that there is no
hard, rocky surface to walk on," Marcy said.
Chief Kepler scientist William Borucki said he thinks
the planet is somewhere between Earth and gas-and-liquid Neptune, but that it
has a lot of rocky material. It's in a size range that scientists don't really
know anything about. Measurements next summer may help astronomers have a
better idea of its makeup, he said.
The planet is 600 light years away. Each light year is
5.9 trillion miles. It would take a space shuttle about 22 million years to get
Kepler spots a planet when it passes in front of its
star. NASA requires three of those sightings before it begins to confirm it as
a planet. Borucki said the third sighting for 22b happened a year ago, just
before the telescope shut down for a while. It took several months to finish the
"It's a great gift," Borucki said. "We
consider this sort of our Christmas planet."