This story’s pretty much everywhere today, though the headlines would probably be more accurate (if more cumbersome and less exciting) if they said that researchers have located the first exoplanet confirmed to be in an orbit around its parent star that would permit the possibility of liquid-phase H2O on its surface, and to have sufficient mass to hold on to a “substantial” atmosphere.

(Kinda takes the magic out of it, this whole accuracy thing… but it’s still pretty awesome when you think about it. Or it is for me, anyway.)

The new planet is one of six orbiting the star Gliese 581, a red dwarf 20 light-years from Earth. Two of the planet’s siblings, dubbed planets C and D, have also been hailed as potentially habitable worlds. The two planets straddle the region around the star where liquid water could exist — 581c is too hot, and 581d is too cold. But 581g is just right. The discovery will be published in the Astrophysical Journal and online at arxiv.org.

The new planet is about three times the mass of Earth, which indicates it is probably rocky and has enough surface gravity to sustain a stable atmosphere. It orbits its star once every 36.6 Earth days at a distance of just 13 million miles.

[…]

Gravity dictates that such a close-in planet would keep the same side facing the star at all times, the same way the moon always shows the same face to Earth.

That means the planet has a blazing-hot daytime side, a frigid nighttime side, and a band of eternal sunrise or sunset where water — and perhaps life — could subsist comfortably. Any life on this exotic world would be confined to this perpetual twilight zone, Vogt says, but there’s room for a lot of diversity.

“You can get any temperature you want on this planet, you just have to move around on its surface,” Vogt said. “There’s a great range of eco-longitudes that will create a lot of different niches for different kinds of life to evolve stably.”

The inevitable disclaimer here is that although it looks like Gliese 581g could support some sort of life, whether it actually does is still something of a cosmological crapshoot with unknown odds. However, the relative ease with which we’ve found it suggests there may be many more planets in similar situations, which raises the chances of us humans not being the only gang in town after all. Those odds are still pretty long, of course… but hey, we can dream, right? Question is, will we find ’em and meet ’em before time runs out?