At Saturn’s north pole, clouds race around a shape that looks as if it was drawn with a ruler. Six broad sides meet at six corners, enclosing a region roughly 30,000 kilometres across. Earth could fit inside it with room to spare. The hexagon is real, but it is not a rigid object and not quite a single storm. It is a powerful eastward jet stream that meanders into a six-lobed wave around the north pole. A separate hurricane-like cyclone spins at…