NASA discovers 'closest twin to Earth'

Jul 23, 2015, 4:06 PM EDT
NASA logo at the Kennedy Space Center. Florida
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NASA, the Seti Institute and other universities have announced that -- using four years’ worth of data from the Kepler space telescope -- they have discovered “the closest twin to Earth” outside the solar system. Additionally, they've identified 12 other possible “habitable” exoplanets. The New York Times reports:

Inching ahead on their quest for what they call Earth 2.0, astronomers from NASA’s Kepler planet-hunting spacecraft announced on Thursday that they had found what might be one of the closest analogues to our own world yet.
It is a planet a little more than one and a half times as big in radius as Earth. Known as Kepler 452b, it circles a sunlike star in an orbit that takes 385 days, just slightly longer than our own year, putting it firmly in the “Goldilocks” habitable zone where the temperatures are lukewarm and suitable for liquid water on the surface — if it has a surface.
The new planet’s size puts it right on the edge between being rocky like Earth and being a fluffy gas ball like Neptune, according to studies of other such exoplanets. In an email, Jon Jenkins of NASA’s Ames Research Center, home of the Kepler project, and lead author of a paper being published in The Astronomical Journal, said the likelihood of the planet’s being rocky was 50 percent to 62 percent, depending on uncertainties in the size of its home star. That would mean its mass is about five times that of Earth.
“This is the first possibly rocky, habitable planet around a solar-type star,” said Jeff Coughlin, a Seti scientist. All 11 previously discovered exoplanets of a similar size and orbit travel around stars that are smaller and cooler than the sun.
“It is the closest thing that we have to another place that somebody might call home,” said Jon Jenkins, a Nasa scientist. The planet is like Earth’s “older, bigger first cousin”, he said.
The research suggests 452b has five times the mass of Earth, is about 1.5bn years older, and has a gravity about twice as powerful as our own.
About 1,400 light years away, Kepler 452b orbits a star similar to our sun, and at about the same distances as Earth orbits the sun, meaning it has a similar length year and exists in the “habitable zone” where liquid water can exist on a planet.