There's a lot of manmade stuff sitting on the surface of the Moon, but some of it is more (ahem) organic than the rest.
Over decades of space exploration the Moon has become littered with crashed satellites, landing probes, lunar modules, lunar rovers and other mission leftovers, not to mention American flags and a plaque left behind to celebrate fallen astronauts. But besides exploring the lunar surface, astronauts also had to actually live on it for stretches of time. For example, during the Apollo 17 mission in 1972, the last moonshot, astronauts Eugene A. Cernan and Harrison H. Schmitt spent nearly three days on the surface, conducting experiments and excursions and picking up samples. Over the course of three days, a man's gotta eat, and if a man eats, a man's gotta...well, you know.
After the lunar landing portion of the mission was over, Apollo astronauts had to lift off from the surface in the lunar module to rendezvous with the command module in orbit around the moon, and given that they'd just picked up quite a few moon rocks to take back to Earth, they had to lighten their load a little bit. Among the things that went overboard to sit on the moon for all eternity were the astronauts' "defecation collection devices."
Yeah, we left poop on the moon.
So, the next time you're staring up at that big silvery orb in the night sky, and you're thinking about how amazing it is that 12 human beings have set foot on it and explored its wonders, just remember that they also did other, less poetic things while they were up there, and left evidence of it for future space tourists to find and giggle at.
(Via Mental Floss)