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This artist's conception illustrates Kepler-22b, a planet known to comfortably circle in the habitable zone of a sun-like star. Caption and image courtesy of NASA/Ames/JPL-Caltech

With thousands of planetary candidates under its belt, NASA’s Kepler mission has finally found a planet that might be just right for life.

The planet, called Kepler 22-b, is a bit more than twice the size of Earth and 600 light years away. “Scientists don’t yet know if Kepler-22b has a predominantly rocky, gaseous or liquid composition, but its discovery is a step closer to finding Earth-like planets,” NASA stated in a release.

This would be Kepler’s first confirmed planet in the Goldilocks – or habitable – zone. This means that the planet is situated far enough away from the sun where it’s not too hot, or too cold. The planet orbits a sun that is similar to ours, too, according to NASA.

This diagram compares our own solar system to Kepler-22. The habitable zone is the sweet spot around a star where temperatures are right for water to exist in its liquid form. Liquid water is essential for life on Earth. The diagram shows an artist's rendering of the planet comfortably orbiting within the habitable zone, similar to where Earth circles the sun. Caption and image courtesy of NASA/Ames/JPL-Caltech

However, not everyone believes the “habitable” distinction is correct. The Planetary Habitability Laboratory (PHL) believes Kepler-22 b is an uninhabitable, Warm Neptunian.

“The recent confirmation of Kepler 22-b does not qualify as a potential habitable exoplanet on the catalog. It is in the habitable zone of the star, but it is too big and classified here as a Warm Neptunian.”

UPDATE: The PHL just provided another updated scenario for Kepler 22-b.

“We modeled now a best case scenario using a mass-radius relationship that assumed an ocean planet with corrected data and things changed a lot. Without mass is very difficult to assess the habitability of Kepler-22b. More observations will be needed to clarify its habitability status. It is so close to a transition point between superterrans and neptunians.”

Even my iPhone’s Exoplanet App (It’s excellent, by the way. A must get!) cautioned readers that, “One should keep in mind that there are large uncertainties in every climate model and our definition of habitability is not well established.”

And remember, if you take a look at the model above, you can see that Mars is also in the habitable zone. Food for thought.

We’re learning more and more about new planetary discoveries, and even as recently as October, we learned that the habitable zone around one specific class of star is larger than once expected.

So while the Kepler 22-b news definitely exciting, I’m sure we’ll hear more about it in the future and we might have a completely different story to share. For example, this past September, the European Southern Observatory announced that it had found 16 “Super-Earths.” However, depending on what website or app you use, that “Super-Earth” figure is different. So what’s the real number? What, if any, planet was re-classified? You don’t really hear much about that.

If you have a reliable source for an exoplanet count, please share it here.

Read about some other Kepler discoveries here.

Later this week, we’ll talk more about the Kepler mission, how it finds planets, and how you can search for planets from your very own computer.

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