Historical contingency

Apparently there's more ice on Mars than we realized. Lots more ice. In fact, Viking 2 came within eight centimetres of uncovering ice on Mars in 1977:

Meteorites that crashed into the Martian surface last year exposed buried ice to the digital eyes of NASA spacecraft. Scientists have used those images to deduce that there is a lot more ice on Mars — and that it's closer to the equator — than previously thought. In fact, subterranean Martian ice should extend all the way down beyond 48...