Mars

Can life exist on Mars today? Once, the red planet was supposed to be dry, lifeless rock. But each new robot probe makes the Mars story more intriguing. First came hints of ancient oceans that vanished a long time ago -- perhaps able to support life back in our own dinosaur era, though not today. Next, Mars showed it probably still has a lot of solid ice just beneath the surface. This year even brought photos strongly suggesting that water flowed down a Martian gully in the past three or four years. a probe called Phoenix Mars Lander raises an old theory from the ashes: There could be Martians alive in that ice today. If so, they'll be microbes that can survive freezing for a very long time, with origins in Mars's warmer and wetter past. After all, scientists digging deep into Antarctica have found "exotic" living microbes in ice that's millions of years old.

This 3-D image of the martian northern polar ice cap, taken by the High Resolution Stereo Camera onboard ESA’s Mars Express orbiter, shows layers of water ice and dust. Credit: ESA/DLR/FU Berlin (G. Neukum)