Boffins: Bebo interstellar spam aliens don't exist after all
Gliese 581d 'too crusty' for civilisation to arise
Gliese 581: The Crustening
However it now seems that in fact Gliese 581d is liable to be lifeless after all. New boffinry suggests that there are other requirements for a life-bearing world than simply being in a star's liquid water zone.
Astro brains in America now say that there is also a requirement that plate tectonics must be taking place on such a world - that is, that the planetary crust must be broken up into mobile bits, causing a certain number of volcanoes, earthquakes and so on. Apparently this is necessary "to pull excess carbon from its atmosphere and confine it in rocks to prevent runaway greenhouse warming".
"If you have plate tectonics, then you can have long-term climate stability, which we think is a prerequisite for life," says Rory Barnes, astro boffin at the University of Washington.
Energy to drive the necessary tectonics can come from radioactive decay within a planet. However it is also driven by tidal forces exerted on a world by another body, as in the case of the tides generated on Earth by the Moon. Where an overly close star or giant planet such as Jupiter generates such forces, they don't merely cause water to slosh about - they also wrack and twist the very planetary crust itself, perhaps causing the place to be uninhabitably plagued by liquid hot molten magma, collapsing mountains and so forth. This happens on Jupiter's moon Io, for instance.
In the case of Gliese 581d, from which Bebo-outraged aliens might retaliate by extirpating the race which could emit such awfulness, it seems fortunately that the tidal forces are probably unsuitable for life.
"Our model predicts that tides may contribute only one-quarter of the heating required to make the planet habitable, so a lot of heat from decay of radioactive isotopes may be required to make up the difference," says Brian Jackson of Arizona Uni, a colleague of Barnes.
Provided that Gliese 581d isn't unusually radioactive, then, there shouldn't be any possibly-irritable aliens there. If it is, of course, we're looking at potentially ill-tempered radioactive mutated aliens who might also be superhumanly strong. (Surface gravity is liable to be a lot more than that of Earth, as Gliese 581d is 7 times Earth's mass.)
Truly, this Web-2.0 stuff is a very bad and dangerous thing. Will the human race realise in time?
There's more from the University of Washington here, including a free link to the relevant scholarly paper. ®