Eight New 'Goldilocks' Planets Discovered, Including Alien Earth

Astronomers have discovered eight new planets in the "Goldilocks" zone of their stars, orbiting at a distance where it's neither too hot nor too cold and where liquid water can exist on the planet's surface. The findings double the number of small planets believed to be in the habitable zone of their parent stars.

"Most of these planets have a good chance of being rocky, like Earth," said Guillermo Torres, the lead author of the paper detailing the findings, in a news release.

Among the eight planets are two that are the most like our own planet Earth to date. Named Kepler-438b and Kepler-442b, these planets orbit red dwarf stars that are smaller and cooler than our own sun. Kepler-438b circles its star every 35 days, while Kepler-442b circles every 112 days.

Kepler-438b actually receives about 40 percent more light than Earth; in comparison, Venus receives twice as much sunlight as Earth. Too much light, and water will just boil away in the form of steam. Too little light, though, and water will freeze solid. In contrast, Kepler-442b receives about two-thirds as much light as Earth, which gives it a 97 percent chance of being in the habitable zone.

"We don't know for sure whether any of the planets in our sample are truly habitable," said David Kipping, second author of the new report. "All we can say is that they're promising candidates."

Of the eight planets discovered, four are in multiple-star systems. However, the companion stars are distant and don't significantly influence the planets.

Current observations are challenge, since the planets are distant from Earth. Kepler-438b is located 470 light-years from Earth, and Kepler-442b is 1,100 light-years. That said, further studies may just tell researchers whether or not these planets actually are habitable, and may contain signs of alien life.

The findings were announced at a meeting of the American Astronomical Society.

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