New Horizons, Pluto, Earth 2.0, Kepler 452b

NASA said Thursday 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.

"Today, Earth is a little less lonely," Kepler researcher Jon Jenkins said.

The planet, Kepler-452b, is about 1,400 light-years from Earth in the constellation Cygnus. It's about 60% bigger than Earth, and is located in its star's habitable zone -- the region where life-sustaining liquid water is possible on the surface of a planet.

 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.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.

Before the discovery of this planet, one called Kepler-186f was considered the most Earthlike,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.

In 2017, NASA plans to launch a planet-hunting satellite called TESS that will be able to provide scientists with more detail on the size, mass and atmospheres of planets circling distant stars.

spacecraft   太空船
habitable     適合居住的
rocky          岩石構成的
constellation 星群
life-sustaining 維持生命
atmosphere  大氣
brightness   亮度；明亮
cataloging  目錄
circling   還騎

What :  in the habitable zone of a star similar to our Earth
Who : NASA researcher
When : Thursday
Where ; NASA
Why : it's the closest match yet found
How ; It takes 385 days for the planet to orbit its star, very similar to Earth's 365-day year


http://edition.cnn.com/2015/07/23/us/feat-nasa-kepler-planet-discovery/