Gliese 581C

Gliese 581 c is the closest you can get to the planet Earth just now – in April 2007 - without being on... Earth.
It is an extrasolar planet orbiting the red dwarf star Gliese 581.
It appears to be in the habitable zone of space surrounding the star, where the surface temperatures of any planets present, might maintain liquid water and therefore be suitable for life as we know it.
The planet is relatively close, at 20.5 light years (193.9 trillion kilometres) from Earth in the constellation of Libra. Its star is identified as Gliese 581 by its number in the Gliese Catalogue of Nearby Stars.