Mars is littered with junk. Historians want to save it.

No astronaut has ever stepped foot on Mars, but that doesn't mean humans haven't left their mark — literally. 

Since 1971 when the Soviet Union's Mars 2 spacecraft crash-landed onto the Red Planet, people have littered the Martian surface with man-made junk, quite a feat from an average of 140 million-miles away. Broken spacecraft debris, parachutes, and rover tracks are just some of the ways our species has disrupted the foreign environment — not to mention the hardy Earthling bacteria it has inadvertently sent there.