The discovery of Gliese 581g, an alien planet orbiting in the habitable zone of its parent star, has added new fuel to the debate over the uniqueness of Earth and whether life exists elsewhere in our universe.
"Any planet is unique in its details, but what we're really asking is: are the general properties of Earth something we can expect to be common in the galaxy, or rare?" said astrophysicist Neil deGrasse Tyson, director of the Hayden Planetarium at the American Museum of Natural History, this week.
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