NASA said that its Kepler
spacecraft has spotted “Earth’s bigger, older cousin”: the first nearly
Earth-size planet to be found in the habitable zone of a star similar to our
own. Though NASA can’t say for sure whether the planet is rocky like ours or
has water and air, it’s the closest match yet found.
The planet, Kepler-452b, is
about 1,400 light-years from Earth in the constellation Cygnus. It’s about 60%
bigger than Earth, NASA says, and is located in its star’s habitable zone — the
region where life-sustaining liquid water is possible on the surface of a
planet.
A visitor there would experience
gravity about twice that of Earth’s, and planetary scientists say the odds of
it having a rocky surface are “better than even.” While it’s a bit farther from
its star than Earth is from the sun, its star is brighter, so the planet gets
about the same amount of energy from its star as Earth does from the sun. And
that sunlight would be very similar to Earth’s, Jenkins said.
The planet “almost certainly
has an atmosphere,” Jenkins said, although scientists can’t say what it’s made
of. But if the assumptions of planetary geologists are correct, he said,
Kepler-452b’s atmosphere would probably be thicker than Earth’s, and it would
have active volcanoes.
It takes 385 days for the
planet to orbit its star, very similar to Earth’s 365-day year, NASA said. And
because it’s spent so long orbiting in this zone — 6 billion years — it’s had
plenty of time to brew life, Jenkins said.
“That’s substantial
opportunity for life to arise, should all the necessary ingredients and
conditions for life exist on this planet,” he said in a statement.
Before the discovery of this
planet, one called Kepler-186f was considered the most Earth-like, according to
NASA. That planet, no more than a 10th bigger than Earth, is about 500
light-years away from us. But it gets only about a third of the energy from its
star as Earth does from the sun, and noon there would look similar to the
evening sky here, NASA says.
The $600 million Kepler
mission launched in 2009 with a goal to survey a portion of the Milky Way for
habitable planets. From a vantage point 64 million miles from Earth, it scans
the light from distant stars, looking for almost imperceptible drops in a
star’s brightness, suggesting a planet has passed in front of it.
It has discovered more than
1,000 planets. Twelve of those, including Kepler-425b, have been less than
twice the size of Earth and in the habitable zones of the stars they orbit.
Missions are being readied
to move scientists closer to the goal of finding yet more planets and
cataloging their atmospheres and other characteristics.
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