criss-crossed with canals and the deep canyons are unlikely to hide fleets of flying saucers primed to swarm down on humanity at a moment’s notice. Instead, it’s a desolate place of rocks, craters and giant mountains, one of which is a 27-kilometre high volcano. Most of the mountains are in the southern hemisphere, and a massive impact millions of years ago left much of the north a dusty basin. It’s a downhill walk to the north pole, should anyone get the chance.