Updated. See below.

Update 2: The artist replies in comments. The art stays! Yay!

Man, I am a sucker for this kind of thing. I’m sure everyone’s heard about the new Earthlike world that has been found in a solar system in our galactic neighborhood: a tad over twenty light-years away. Now they’ve got the artwork up, and I can’t resist a post.

Just like planets, stars (and even galaxies, some say) have habitable zones (a/k/a/ the Goldilocks Zone). In the case of stars, there is a minimum and a maximum distance from that sun wherein life (as we know it, at least) can exist: those planetary orbits where the mean global surface temperature on the planet ranges between 273 and 373 Kelvin (that is, between 32^o and 212^o Fahrenheit). In other words, life as we know it cannot exist without liquid water.

Obviously, a lot of things besides solar radiation determine the temperature on the surface of the planet. One important factor is the planet’s albedo, or how reflective it is. Just as light-colored cars heat up less on a hot summer day in a parking lot than the dark ones do, a light-colored world, such as one covered in ice or high white clouds, or light-colored rock, reflects much more heat back into space than a darker world. Another factor is how good that planet’s atmosphere is at holding onto heat—how high a concentration of greenhouses gases, such as carbon dioxide and methane, it has. (Without at least some greenhouse gases, Earth would be an ice ball.) And so on.

Gliese 581’s “Earthlike” world is very different from our own. Gliese 581c is five times as massive as Earth, scientists estimate, and one and a half times as large, so the gravity there would be about twice ours. It’s only a few million miles from Gliese 581, and thus its year only lasts 12.9 days. However, Gliese 581 is a red dwarf, and much weaker than our own sun, so the world would still be habitable (in terms of temperature, at least) at that orbital distance. (It boggles my mind sometimes, when I sit outside on a sunny day and feel the sun’s heat on my face, that I am ninety-three fucking million miles from the sun—which, to put things in perspective, means that if you could drive your car all the way, going an average of 60 mph, it would take you about 177 years to get there. Or if you took a jet going 650 mph, it would take more than sixteen years—and it can still give me second degree burns, if I stay out too long without sunscreen.) This is the third world found around Gliese 581.

Gliese 581c is almost certainly tidally locked to its sun, just as Mercury is to our sun, and our moon is to us: this means it would rotate on its axis only once for every orbit around the star, and thus would show only one face to the sun—which has important implications for heat transfer and so on. Though it could be in a 2:3 tidal lock, which would allow for a sunrise and sunset…

They actually don’t know whether there is water on Gliese 581c yet, though they are pretty sure it is a rocky world, like ours. Here’s the cool thing: it might be possible for them to get a glimpse, using spectral analysis, of the atmosphere of this planet. They may be able to tell what the chemical composition is. And while it’s highly unlikely, if they found the presence of significant quantities of oxygen, that would almost certainly mean that there was life on that world.

This is because oxygen is highly reactive, and combines very readily with other elements: with carbon, to make carbon dioxide (and fire); with silicon, to make rock; with iron, to make rust—just to name a few. It is very rarely found all by itself. Unless there is some ongoing process—such as plant respiration—to produce it. It is possible to imagine that there might be some unknown, non-biological process that would convert (the technical term is “reduce”), say, iron oxides, to iron and oxygen, or carbon dioxide to carbon and oxygen. But applying Occam’s Razor, it ain’t bloody likely.

Would that not be cool??
___________

PS- Click on the link for the bigger image; it’s really gorgeous.

___________

Update: I loved this image so much I went back and studied it more closely, and followed the links back to the artist, Karen Wehrstein’s, blog. She has some really cool stuff there: intriguing artwork, very much informed by her love of SF and science. She is also a published SF writer, and a regular poster at Daily Kos.

Because NASA’s images are usually public domain, I had just assumed this image was also, but when I went back and looked more closely, it is indeed copyrighted. I have contacted Karen Wehrstein to get her permission to leave this image up, but its days here may be numbered. Watch this space for more info.