For bots like Scarab to be able to explore hostile planets completely unsupervised, researchers must write its complex behavioral software here on earth and then test it to see how it works. For that there is Zoe, a survey rover that researchers have dispatched several times to the Atacama Desert in Chile alone. "We just drop her there and leave," says Wettergreen, who describes Zoe as a giant fluorescence-imaging camera that searches the desert soil for microorganisms.

To navigate autonomously, it uses a panoramic imager made of a triplet of high-resolution cameras mounted on a necklike pan-tilt mechanism. With these cameras, Zoe can not only traverse obstacles but also establish waypoints and create maps of the nearby terrain that help it make decisions about steering and direction.