Monday, February 10, 2014

It Might Be Time We Look for Superhabitable Exoplanets


A concept drawing of exomoons orbiting a gas giant. Image: René Heller, AIP/McMaster University.

The term “super Earth”a type of exoplanetis a little misleading. Our Earth is pretty super, what with its breathable air and a temperate climate, so a super Earth sounds a little like a planet with a nicer atmosphere and an even more temperate climate. It’s not. A super Earth is simply a planet that has a mass higher than Earth’s but lower than the ice giants Neptune and Uranus. But there are exceptions to every rule, like the super Earth astronomers think might be super habitable—i.e. more habitable than Earth.

We tend to think of habitable worlds as those planets that orbit in their parent star’s habitable zone; that is, a planet the right distance from the star such that it’s warm enough for water to exist in a liquid form on its surface. Since Earth is the only habitable planet we know, it’s the planet that has shaped our definition of what a habitable planet is.

But the more we study planets and moons, even those in our own solar system, the more we’re forced to revise that definition. To be habitable, a world doesn’t have to be in a star’s habitable zone. Other factors like tidal heating have to be taken into account, a phenomenon that could make planets far from their stars habitable, or planets close to their stars inhabitable. Astronomers René Heller and John Armstrong have a new term for these potentially habitable worlds that don’t fit the conventional definition: “superhabitable.” Their full paper is available on Arxiv.

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