Astronomers discover eight new 'Goldilocks' planets in Milky Way

Astronomers announced Tuesday the discovery in the Milky Way galaxy of eight new planets orbiting their stars at the perfect distance to have liquid water, and thus the potential to host life. Two of the planets are the more similar to Earth of any other known planets outside the solar system, the astronomers said.

Many scientists describe such planets as being in the “Goldilocks zone,” as they orbit their stars at the ideal distance to create an Earth-like temperature. If a planet is too close to its star, any water on its surface would be too hot and would evaporate, but if too far away, water would freeze — like Goldilocks’ porridge in the “Three Bears” fairy tale, the temperature must be “just right.”

Astronomers from the Harvard-Smithsonian Center for Astrophysics (CfA) said they have found eight planets in this zone. Two appear to be very Earth-like, leading scientists to believe they could be habitable. One, dubbed Kepler-438b, is just 12 percent larger than Earth and receives about 40 percent more light; another, named Keppler-442b, is one-third larger than Earth and gets about two-thirds as much light.

"Most of these planets have a good chance of being rocky, like Earth," CfA astronomer Guillermo Torres said in a news release.

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

Torres and Kipping’s findings were published in the Astrophysical Journal, and presented Tuesday at the annual meeting of the American Astronomical Society in Seattle.

The planets were discovered as part of NASA’s Kepler mission, which was launched in 2009 and sent a spacecraft with a powerful telescope to observe the billions of planets and stars in the Milky Way. Kepler’s goal is to survey the galaxy for planets that are most Earth-like — orbiting starts that are most Sun-like — and thus determine whether they could be habitable.

Kepler has discovered hundreds of planets, but not many that are both Earth-sized and likely to have liquid water. In April 2014 the mission spotted Keppler-186f, its first planet that was similar in size to Earth — most were at least 40 percent bigger — and was also in the Goldilocks zone, but it receives far less light. 

In 2011, Kepler found hundreds of new Milky Way planets, five of which were both in the Goldilocks zone and similar in size to Earth.