Dread

Last month, the Mars Reconnaissance Orbiter took time out from mapping the surface of Mars to take high-resolution photographs one of the red planet's two small moons, Diemos. Like Phobos, Diemos is probably a captured asteroid, and it's relatively small, with a semi-major axis of just 12 kilometres. Pictures just released show a smooth, reddish surface pockmarked with old and more recent craters. Apparently, the surface darkens and reddens when exposed to vacuum and sunlight, so the paler areas have been recently disturbed (in relative terms), either by impact or by material sliding down the slopes of ridges. Many asteroids probably look more or less like this; dusty desert mountains pitted and battered by impacts. The old science-fiction notion of hollowing them out into giant cities isn't viable - they're basically huge rubble piles cemented by gravity - but it would be easy enough to excavate cut-and cover tunnels in the dusty durface, or maybe throw up a tent over that sharp-rimmed crater in the centre. It's about two kilometres across, not a bad size for a town...