NASA's Kepler spacecraft spots planet 'somebody else might call home'

Traci Watson | Special for USA TODAY

Show Caption Hide Caption Earth 2.0? NASA finds planet with possible habitable zone Scientists have spotted a planet much the same size as our Earth orbiting a star that closely resembles our sun. USA TODAY'S Shannon Rae Green and reporter Doyle Rice explain what makes a planet habitable.

Scientists have spotted a planet much the same size as our Earth orbiting a star that closely resembles our sun, making this new world the most likely known place outside our solar system to harbor life.

The newfound planet, referred to as Kepler-452b, “is the closest thing we have to another place that somebody else might call home,” Jon Jenkins of NASA’s Ames Research Center told reporters Thursday. The planet has been at just the right temperature to boast liquid water for some 6 billion years, “a considerable time and opportunity for life to arise somewhere on its surface or in its oceans,” assuming the place has all the necessary ingredients for life, Jenkins said.

Researchers have found other planets outside the solar system that are nearly the same size as the Earth and that are probably rocky, as Earth is. But those planets circle dim, cool stars very different from our own sun, whereas 452b is hitched to a star very much like ours. If we could send plants to 452b, Jenkins said, they could comfortably photosynthesize.

"We want to find planets around solar-type stars like our sun, because we’re here on Earth and we know that there’s life here, and we’re around a solar-type star,” Jeffrey Coughlin of the SETI Institute told reporters today.

The new planet is about 60% bigger in diameter than Earth, the researchers said. It has a better-than-even chance of having a rocky surface, which would make a good platform for life to gain a foothold. Assuming it’s rocky, it would have active volcanoes and perhaps a thick atmosphere.

This new Earth cousin was spotted by NASA’s Kepler telescope, which watched for barely perceptible dips in the amount of light coming from stars in the constellations Lyra and Cygnus. A slight dimming signals that something, perhaps a planet, is blocking some of the light emanating from the star. After checking and re-checking, the researchers are confident that the dimming signals an actual planet and not a false alarm. The planet, which is some 1,400 light-years from Earth, is described in a new article in The Astronomical Journal.

Other scientists who were not involved in the research called 452b an exciting example of a planet in the “Goldilocks” zone, where it’s neither too hot nor too cold for liquid water to persist.

“You could say this is the first viable ‘Goldilocks’ planet—with dozens more potentially,” said MIT astronomer Sara Seager via email.

All the same, it’s not clear that 452b is rocky. It could be made of ice, or it could have a thick hydrogen envelope that would choke off the possibility of life, said astronomer Joshua Pepper of Lehigh University.

“We’re getting closer and closer to a true Earth analog,” Pepper said. “But it’s going to take a long time before we can confirm whether these planets are really Earth-like.” That’s because it will be very difficult to measure the mass of 452b and similar planets, he said, which in turn will make it hard to know whether they are rocky.

“Since we don't know anything else about the planet, like its composition and atmosphere, it is hard to tell how good actually is this planet for life,” said planetary scientist Abel Mendez of the University of Puerto Rico at Arecibo via email.

Even if 452b turns out to be a dead world, Kepler has cornered seven more possible planets in the “habitable zone” where there could be liquid water, Coughlin said. If those candidate planets are confirmed, “there are some really interesting discoveries on the horizon.”