But liquid water isn't necessarily needed for all life. All water really does is provide a medium and a promiscuous electrical charge to kickstart the biochemical reactions that keep Earth-like life humming along at a steady clip. In theory, any kind of medium that provides a dance floor on which chemicals can boogie would do, but that life might not look like life as we know it.
Given that, life - or something like it - might exist in our very own solar backyard. Enter Titan.
Titan is the largest of Saturn's 83 moons, coming in at just a bit under half the size of Earth. At more than 880 million miles from the sun, Titan's atmosphere sits at a balmy -290° F. At this deep-freeze, water only exists as vapor in the highest reaches of Titan's atmosphere. Yet, lakes pockmark Titan's surface. These lakes are made not of liquid water, but of liquid methane.
After a tip from the Hubble Space Telescope suggested that Titan had methane lakes, the Cassini-Huygens mission spotted and confirmed them. The presence of methane lakes makes Titan the only other known place in our solar system to have stable bodies of liquid sloshing around on its surface.