habitable world, called Gliese 581g, is about three times the mass of Earth and orbits its star once every 36.6 Earth days, reported astronomer Steve Vogt of the University of California, Santa Cruz. That orbit plants it close enough to the star that it ought to be tidally locked, showing the same face to the star at all times.

This setup would likely leave one hemisphere a scorching desert and the other a frigid ice sheet. With the right amount of global warming, either or both sides could conceivably be habitable. But the most comfortable place for life to grab a toehold would probably be in the zone of permanent twilight, where the sun is always rising or setting.

Or so Vogt assumed. In a new paper submitted to the Monthly Notices of the Royal Astronomical Society, Vogt and atmosphere modeling expert Kevin Heng of The Swiss Federal Institute of Technology Zurich find that the planet’s most comfy spots probably lie along a sideways V-shaped curve, with two eddies of warmth at the tips.

“What we’re finding basically is that the patterns of warmth and cold on these things is a little more complicated,” Vogt said. “In fact the most comfortable place is probably around the chevron, in the vortices.”

The still-unconfirmed planet was detected via subtle gravitational tugs on its parent star, which had to be teased apart from the conflicting signals of five sibling planets that range from about two to 15 the mass of Earth.

This planet-hunting method gives no data on what the planet looks like, however. Future telescopes may be able to snap fuzzy pictures of Gliese 581’s planetary family. But until then, the alien atmospheres are up in the air.

To bring Gliese 581g’s possible climate down to Earth, Vogt and Heng modified a simplified climate model often used to simulate Earth. In recent years, Heng and others have started using the modeling package to simulate atmospheres on gas giant exoplanets.

“As soon as I heard about this I thought, let’s turn it loose on Gliese 581g and tell me where the aliens are living,” Vogt said.

The researchers scaled the model’s temperature parameters to reflect the heat Gliese 581g would absorb from its parent star, which is dimmer but closer than ours. They set the temperature at the equator to about 40 degrees Fahrenheit, and assumed the temperature difference between the equator and the poles was similar to Earth’s, about 60 degrees. The team also assumed certain properties of the atmosphere, like the amount of heat it can absorb and the surface pressure, were just like Earth’s.

The team ran the model for 1,000 Earth days to see what long-term weather patterns showed up. They found a constant light wind, like a slow jet stream, developed around the planet, pulling warm air into a V-shape. That whole V would probably be habitable, Vogt suggests. Extra whorls of warmth in the north and south “might be nice vacationing spots,” he said.

“It’s a great start for understanding the patterns of flow on these super-Earth exoplanets,” said exoplanet expert Sara Seager, who was not involved in the new study. “It’s pretty cool that even under all these approximations and assumptions, he always finds spots that are habitable. That’s reassuring.”

But don’t pack your bags yet. A separate group of astronomers announced Oct. 12 that the planet might not be there at all, and could just be a trick of the data.

“Personally, I have to admit that this debate on habitability seems a lot less relevant if Gliese 581g doesn’t actually exist,” said astronomer Heather Knutson of the University of California, Berkeley, who models the atmospheres of hot gas giant exoplanets. “Given all of the other transiting planets currently being discovered by the Kepler mission, I think we’ll probably have an actual, confirmed planet in the habitable zone… in the next one to two years.”

Vogt is undeterred. “Whether or not Gliese 581g is confirmed, there’s going to be others like this,” he said. “‘What is life like there?’ is becoming an interesting field in its own right. We have enough computing power now to make some interesting conclusions about where things might live.”

Video: Heng & Vogt/MNRAS. Image: Heng & Vogt/MNRAS.

See Also:

• A Habitable Exoplanet — for Real This Time
• Exoplanet Wars: “First Habitable World” May Not Exist
• First Direct Image of Multiple Exoplanets Orbiting a Star
• Exoplanet Hunters Finally Catch One in a Star’s Debris Disk
• Most Earth-Like Extrasolar Planet Found Right Next Door

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Authors: Lisa Grossman

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