Are the materials used in the rover wheels too exotic? I'm metallurgist, but I know that steel, though heavy, is malleable and, if correctly tempered, unlikely to break like the rover's wheels. At what cost ultralight, exotic metals?

Edit: Are they really made of aluminum? If so, while hardly exotic, definitely more brittle than steel. I know steel is heavy as hell, but of course you can use a thinner steel for an equivalent strength (still heavier I suppose).