The National Science Foundation (NSF) announced findings by several astronomers on Wednesday that they have found a planet on which the "chances for life on this planet are 100 percent,” as was stated by Steven Vogt of the University of California at Santa Cruz, one of the co-discoverers of the planet, in an AP article.
Based on the paltry information these astronomers have to work with, this statement is ludicrous. Even if they were to say there is a fifty percent or even a twenty percent chance, that would still be pie-in-the-sky daydreaming.
The only things they “know” about Gliese 581g are its mass, its distance from its sun Gliese 581, and its orbital period. Everything else they know is inferred from these few facts.
And the reason they know so little is that they didn’t find this planet through the end of an optical telescope and see it, or send a space probe to look at it. Nope. Instead they used a sketchy (to me) twenty year-old technique, which surmises a planet’s existence by measuring variations in the star's radial velocity. This is basically the star’s velocity as it appears to astronomers in spectrographs, which can be affected by the tugs of planets as they circle the central star. It’s sort of like staring at a tree on the side of the crowded New Jersey Turnpike and watching the leaves blow, and then guessing what kind of vehicle just went by. And who was driving it.
So for all these astronomers (and media pundits) know, Gliese 581g is a rock like Mercury or the Moon, bigger, but still just a rock.
But because this planet, which is supposedly three times larger than Earth, resides in what they call the Goldilocks zone (a place in a solar system a certain distance from a sun where a planet could support liquid water), a lot of energy is being given to the idea that it might have some form of life on it.
Let us recognize that Venus, an extremely inhospitable planet in our solar system, resides in this solar system's Goldilock's zone. It is its poisonous and thick atmosphere that make it uninhabitable, not to mention its 800 degree surface temperature.
The planet Mars also resides in the Goldilocks zone and may have had life on it, or may have never had life on it. It would most likely have liquid water on it now if it had a slightly denser atmosphere, and were therefore warmer. This may have been true in the past. The point is, it doesn’t now.
There is a moon of the planet Jupiter called Europa which may very well have life on it in liquid oceans under its cracked, but frozen surface. This extremely cold place is well outside the sun's Goldilock's zone.
The Washington Post article concerning this story also says that there are six or seven planets including Gliese 581g closer to this star than Earth is to our own Sun, including at least one Jupiter-type planet.
The close orbital proximity of all these large planets may wreak upon Gliese 581g unknown effects due to gravitational interactions between them. For instance, very large planets tend to attract or divert more asteroids and comets, possibly causing life-killing sized asteroids to smash into the surface of said planet at a more frequent rate than happens on Earth. It has been suggested that the dinosaurs and other animals on Earth may have been killed at one or more times by asteroids which smashed into the planet like 10,000 nuclear bombs causing a dust induced winter which killed off all but the heartiest species. This would make things very inhospitable for life if it happens once, but if too often, then life will never have a chance to get going before the next global killer comet or asteroid.
The very idea of a Goldilock's zone is something which is misleading and the press and the public are eating it up because it makes for great press. There are so many factors to consider beyond saying "Here is a rock that's in the right place, so it must have water and life on it."
Since there is no evidence that this is anything but a rock at a supposedly propicious distance from its sun, inferences beyond this are irresponsible, media grabbing, and wild speculation. Let's wait until we have real evidence in hand before making claims like these or even suggesting them.