IT'S NOT A ROAD EXACTLY, but the widest trough in Nili Fossae stands atop scientists' wish-list of places to send the next NASA Mars rover to look for signs of life. The valley spans about 26 kilometers (16 miles) wide, and the hills flanking it contain clay sediments, which point to water (and potential life) in the past. This view looks southwest; click on the image for a higher-resolution (1.1 MB) version.

Image credit: NASA/JPL/Arizona State University, R. Luk (vertical exaggeration about 2x)