Meet Gliese 581g, the alien planet that's 'just right' for life

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Dec 14, 2012, 4:31 PM EST

As anyone who can type "Gliese 581" into Wikipedia knows, there are six planets orbiting this red dwarf star. But one of these things is not like the others. Because astronomers at the Keck Observatory in Hawaii have determined that one of them, Gliese 581g, may be able to sustain life.

Scientists have discovered more than 500 exoplanets, that is, planets outside of our solar system. But none of them are considered fit for human habitation. What makes Gliese 581g special?

It turns out that planet g is about 13.5 million miles from Gliese 581. In our own solar system, this would make the planet more of a cauldron than Mercury, which is 36 million miles away from Sol. However, Gliese 581 is a red dwarf, which is cooler and emits less heat and luminosity.

As an astronomer in the Lick-Carnegie Exoplanet Survey says, Gliese 581 falls squarely in "the Goldilocks zone."

"The Goldilocks zone is the range of orbits around any star where it's neither too hot nor too cold but just right for liquid water to exist on the surface. And that's a key ingredient for the existence of life."

Still, planet g is "tidally locked" to Gliese 581, which means it does not rotate; the side facing the sun would be Heat Miser hot, and the side turned away Snow Miser cold.

Fortunately, the twilight zone between light and shadow (actually known as the "terminator") would be fit for human life.

Or maybe even life as we DON'T know it.