In 2004, NASA landed its Opportunity rover on Mars. Initially intended to run for 90 days, it's now spent 11 years trundling around the planet. At this rate, it will still be roaming around on the red rust by the time we terraform the place.
Or, as Randall Munroe's mouseover text on today's XKCD imagines, it could all end badly:
"We all remember those famous first words spoken by an astronaut on the surface of Mars: "That's one small step fo- HOLY SHIT LOOK OUT IT'S GOT SOME KIND OF DRILL! Get back to the ... [unintelligible] ... [signal lost]"