Wednesday, May 18, 2011

Gliese 581d: Rocky, Close (sort of), and Liquid Water (could be, maybe)

"Is the Rocky Alien Planet Gliese 581d Really Habitable?"
Mike Wall, (May 17, 2011)

(Zina Deretsky, National Science Foundation, via, used w/o permission)
"The orbits of planets in the Gliese 581 system are compared to those of our own solar system. The Gliese 581 star has about 30 percent the mass of our sun, and the outermost planet is closer to its star than we are to the sun. Gliese 581d might be able to sustain liquid water on its surface."

"A rocky alien planet called Gliese 581d may be the first known world beyond Earth capable of supporting life as we know it, a new study suggests.

"Astronomers performing a new atmospheric-modeling study have found that the planet likely lies in the "habitable zone" of its host star - that just-right range of distances that allow liquid water to exist. The alien world could be Earth-like in key ways, harboring oceans, clouds and rainfall, according to the research.

"This conclusion is consistent with several other recent modeling studies. But it does not definitively establish that life-sustaining water flows across the planet's surface.

"The new study assumes that Gliese 581d, which is about seven times as massive as Earth, has a thick, carbon-dioxide-based atmosphere. That's very possible on a planet so large, researchers said, but it's not a given. [Video: Life-Sustaining 'Super Earth' Gliese 581d]..."

Gliese 581 is quite close to Sol, our sun: light from Gliese 581 takes only about 20 years to get here. That's close, compared to nearly every other star in this galaxy - but it's still a respectable distance.

The Lemming's posted about Gliese 581's planetary system before: including Gliese 581 g, the planet that either exists - or doesn't. The last that the Lemming heard, astronomers are still discussing whether the numbers add up to a planet - or a sort of statistical blip in observations.

Even though 20 light years is 'close' by galactic standards: it's still a long distance, and those comparatively small planets don't have all that much effect on their star.

The Lemming's excited by the possibility that there's liquid water on Gliese 581d - but let's remember that the dense carbon dioxide atmosphere is possible, not observed.

Another detail, discussed in the article. Gliese 581d is (probably) tidally locked, with one side always facing Gliese 581, like Moon has one face always facing Earth. When the planet was detected, astronomers assumed that it'd be baked on the sunward (starward?) side, and frozen on its night side.

Since then, folks who study atmospheres put together a more sophisticated model - and found that winds could carry heat from the hot side to the cold side, and cold back around to the day side.

Gliese 581d, even if it had that thick atmosphere, and water, and life, still wouldn't be the sort of 'class M planet" of Star Trek - but then, Earth may not be a 'class M planet, either. (May 2, 2011, December 5, 2009)

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