NASA's Martian rover Curiosity is five times larger than its predecessors — about the size of an SUV — says Wired UK's Mark Brown. The energy needed to power it comes from a radioisotope power system. But researchers at the US Naval Research Laboratory would like to develop rovers about the size of a bag of sugar, and as such, need a smaller way to power the machines, Brown says. Well, you can't get much smaller than a microbe.