Have you seen this? Have you heard about this? European astronomers announced yesterday the discovery of an Earth-like planet orbiting the star Gliese 581, 20.4 light years away, in the constellation Libra. Nothing is certain, of course, but early indications are that the planet, Gliese 581 c, has an atmosphere and an average surface temperature similar to Earth. It was also suggested — though this might just be those giddy astronomers getting ahead of themselves — that the planet might have liquid water, which means it could also be capable of supporting life.
Don't get the wrong idea when I say "Earth-like." Gliese 581 c is estimated to be 50% larger than Earth, with perhaps five times the mass. That means gravity on c is about twice as strong as on Earth. c also orbits 14 times closer to its sun, a red dwarf star smaller and cooler than our Sun. That sun could appear twenty times larger than our Moon in the sky over c. Some astronomers also theorize that c doesn't rotate, meaning it has one side of perpetual day and one side of constant night. We know all of this from interpreting data from radio telescopes. The planet's never been viewed through an optical telescope, never been photographed (too small and too far away), so it probably looks nothing like that picture over there. Still, isn't it nice to dream?