This weekend, NASA's Opportunity rover spent its 5,000th day on Mars. While that is a feat in and of itself, it's even more impressive when you consider that it was only planned to last 90 Martian days, or sols. Both Opportunity and its companion rover Spirit were launched towards Mars in 2003, landing on two different parts of the planet in January 2004. Neither were expected to make it through Mars' harsh winter though, which lasts about twice as long as ours and is severely lacking in light, but NASA's team discovered that pointing the rovers towards the north and towards the sun was enough to keep them powered through the winter. Further, making sure the rovers were on north-facing slopes each winter helped to keep them going for years longer than they were ever intended to function.