Nature | Nature News Blog

Kepler scores potentially habitable planet

kepler22b.jpg Kepler, NASA’s planet hunting mission, has bagged its first ‘Goldilocks’ planet, one that sits in the habitable zone of its star.

Kepler 22-b is not an Earth twin: at 2.4 times Earth’s radius, it could be more like a gassy Neptune than a rocky planet (artist’s impression at right). But it sits in a comfortably warm orbit from its host star at temperatures similar to those experienced by Earth.

The team got a third blip on its light curves just before Christmas in 2010 — enough to make Kepler 22-b a candidate — and then spent another full year trying to confirm the planet, with follow-up observations from other telescopes in space and on the ground.

“We consider this our sort of Christmas planet,” says principal investigator Bill Borucki, of NASA’s Ames Research Center in Moffett Field, California, who spoke to scientists today at the first Kepler science conference.

The Kepler team also was preparing to unload another instalment of its catalogue, which now includes 2,326 planet candidates. Among these candidates are 207 Earth-sized planets (in orbits of any period), and 48 planets (of any size) in the habitable zone. Natalie Batalha, the Kepler deputy science team lead at Ames, says that in the current catalogue, there is just one Earth-size candidate in the habitable zone, and that this candidate’s host star has some uncertainties that could push it out of its sweet spot.

Kepler 22-b is not the first discovery in the habitable zone. There have been two discoveries from HARPS, a European instrument team on a ground-based telescope. But neither of those planets orbits a solar-type star. Kepler 22-b, on the other hand, has a 290-day orbit around a star very similar to the Sun. “It’s almost a solar twin,” says Batalha. “I find it very compelling.”

Image credit: NASA/Ames/JPL-Caltech

Comments

  1. Report this comment

    René Heller said:

    Various uncertainties, especially concerning the planet’s mass and its possible cloud coverage, indicate that Kepler-22b is as promising a target for habitability studies as Gl581d. While Gl581d is supposedly too cold, Kepler-22b might be too hot (and eventually too massive) to provide habitable conditions at its surface.

    Since its host star has a somewhat higher luminosity than the Sun and planet b orbits at ~0.88 AU, this Super-Earth straddles the insolation habitable zone at the inner edge.

    This post bases on private communication with my colleague Rory Barnes (Astronomy Department, Univ. Washington, Seattle) who has done some calculations on Kepler-22b today.

  2. Report this comment

    Mary Graham said:

    Is it possible at this early stage to estimate how “old” it is? It has a sun. Does it have any moons?

  3. Report this comment

    John Z. Pietrzyk said:

    How far from Earth is Kepler 22b? Is it a member of a solar system?

    Of the 2,326 exoplanets reported, how many display solar system arrangments similar to ours?