Tales of alien abduction and SETI's extrasolar search for intelligent life may fuel the imagination, but astrobiologists know that the first proof that we are not alone is likely to be found in our own solar system. And rather than being a bug-eyed humanoid, E.T. will probably resemble the extremophile microbes living here on Earth.

Scientists are looking to these hearty single-celled organisms for insight into how life can exist in inhospitable environments. With every new microbe discovered thriving in a place formerly thought to be uninhabited, more extraterrestrial environments are realized to have the potential to support life. Visit our image gallery comparing possible extraterrestrial ecosystems to their terrestrial counterparts.