NASA's Kepler Mission Finds Planet in Habitable Zone: Kepler-22b

Artist's rendering of Kepler-22b

The planet-finding Kepler space mission has discovered a planet 2.4 times the diameter of Earth in the liquid water habitable zone (the region around a star where temperatures are neither too high or too low for liquid water to exist) of a star 600 light years away. This is the first confirmed planet in the habitable zone of a star to be found by Kepler, but many more may be on the way. 

The planet's confirmation was announced Monday by NASA along with other discoveries by its Kepler telescope, which was launched on a planet-hunting mission in 2009.

"This is a phenomenal discovery in the course of human history," Geoff Marcy of University of California, Berkeley, one of the pioneers of planet-hunting outside our solar system, said in an email. "This discovery shows that we Homo sapiens are straining our reach into the universe to find planets that remind us of home. We are almost there."

“Kepler 22b is exciting for two reasons; one, because it is right smack in the middle of the habitable zone,” says Natalie Batalha, Kepler’s deputy science team leader from NASA’s Ames Research Center “The second really exciting reason is that it is orbiting a star very similar to our own Sun, it’s a solar twin.”

Although the planet lies 15 percent closer to its star than Earth does to the Sun, Kepler 22b’s star is a little dimmer and cooler than the Sun, so the planet can get away with being a bit closer. However, exactly what this planet is like is a bit of a mystery: being in the habitable zone isn’t enough to state that a planet is habitable – it requires an atmosphere for starters. Worlds of this size are however a bit of a mystery at the moment.

"If this planet has a surface, it would have a very nice temperature of some 70° Fahrenheit [21°C]," says William Borucki of NASA's Ames Research Center here, who is the principal investigator of NASA's Kepler space telescope. "[It's] another milestone on the journey of discovering Earth's twin," adds Ames director Simon "Pete" Worden.

Unfortunately, the true nature of the planet, named Kepler-22b, remains unknown. It is 2.4 times the size of Earth, but its mass, and hence its composition, has not yet been determined. "There's a good chance it could be rocky," Borucki says, although he adds that the planet would probably contain huge amounts of compressed ice, too. It might even have a global ocean. "We have no planets like this in our own solar system."

The planet is 600 light years away. Each light year is 5.9 trillion miles. It would take a space shuttle about 22 million years to get there.

Watch the press conference announcing the discovery of Kepler 22b (vid is over an hour long)

A shorter news coverage of the findings: