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Super-Earth on 'edge of habitability'

NASA / msnbc.com

Planetary scientists are working on equations to assess how habitable a given planet might be.

Planet-hunters say they've developed a relatively simple method for determining how livable a faraway world might be, and they've used the formula to identify a top candidate: a super-Earth that's 36 light-years away.

The research paper was submitted to the journal Astronomy and Astrophysics just two weeks ago, but it's quickly making the rounds among those who follow the accelerating search for planets beyond our solar system. The big reason for all the interest is that the paper points to a new prospect for the short list of potentially habitable planets: HD 85512 b, a world that's at least 3.6 times as massive as Earth, circling an orange star in the constellation Vela.

The authors — Lisa Kaltenegger of the Harvard-Smithsonian Center for Astrophysics, and Stephane Udry and Francesco Pepe of the University of Geneva — rank the extrasolar planet right up there with Gliese 581d, a prime prospect for habitability that is 20 light-years from Earth. "HD 85512 b is, with Gl 581d, the best candidate for exploring habitability to date, a planet on the edge of habitability," they say.

The paper uses HD 85512 b as a test case for a set of equations aimed at assessing how livable a particular planet might be, based on its orbital parameters, how much radiation it gets from its parent sun and the nature of its atmosphere. HD 85512 b's minimum mass and orbital parameters were published only recently, based on data from the HARPS-Upgrade GTO planet search.  The world orbits a star that is significantly dimmer than our own sun, at a distance of 0.26 AU — which is within Mercury's orbit in our solar system. It makes one full orbit every 58.4 Earth days, the researchers report.

The researchers assume that HD 85512 b is a rocky planet with an Earthlike atmosphere containing water vapor, carbon dioxide and nitrogen. If that's the case, and if more than half the planet is covered by clouds, then it "could be potentially habitable," they say.

Is there a way to resolve those "ifs"? Comparing the planet's mass with its size could tell astronomers whether its composition is more like Neptune's or Earth's. But to study its atmosphere, we're going to need a bigger telescope.

Here's how Kaltenegger explained the challenge to Skymania News: "As to whether it is really habitable, we’ll need a spectrum to tell that — direct imaging would be the ticket. With a direct imaging mission we could detect if it looks habitable. We could detect clouds if we had a big enough telescope in space."

It could be a long time before there's a telescope (or an interferometer) big enough to take on that job. But even now, Kaltenegger and her colleagues say that their research provides "a simple set of parameters which can be used for evaluating current and future planet candidates ... for their potential habitability."

How long will it take to whip up a top-ten list for extrasolar emigration? Weigh in with your comments below.

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