Humans have left a ton of stuff on the moon. Ok, it's more like 200 tons.

From experiments and commemorative plaques to the leftover carcasses of dead space probes and lunar rovers, the moon's got it all. It even has astronaut poop.

Some of the stuff left on the moon is functional, for example astronauts on the Apollo 11, 14 and 15 missions and the Lunokhod 1 and 2 missions each left behind 2-foot-wide panels studded with mirrors pointing at Earth. These "lunar laser ranging retroreflector arrays" are used by NASA to measure the distance between the Earth and the Moon.

"Using these mirrors," Carroll Alley, a physics professor from the University of Maryland, said in a NASA report. "We can 'ping' the moon with laser pulses and measure the Earth-moon distance very precisely. This is a wonderful way to learn about the moon's orbit and to test theories of gravity."

Much of the stuff left up there is junk, though. Wikipedia's list of man-made objects on the moon comes in at 73 moon probes, rovers, and satellites that have been landed or crashed on the moon's surface and left up there since 1958, many from the United States and Russia. These items total a whopping 394,178 pounds (or 178,796 kilograms) of man-made junk left up there.

Humans have also left a bunch of commemorative stuff on the moon, including the six flags deposited by the Apollo missions (five of which are still standing). Golf balls hit by Alan Shepard during his Apollo 14 mission are probably somewhere on the surface, but their location hasn't been pinpointed.

Alan Bean, the fourth man to walk on the moon (during the Apollo 12 mission), left a silver pin on the surface. The Apollo 11 mission left a gold olive branch, a commemorative plaque, and a silicon disk carrying statements from Presidents Nixon, Johnson, Kennedy, Eisenhower and the leaders of 73 other nations.

The Apollo 15 astronauts left a 3 inch "fallen astronaut" statuette on the surface of the moon in 1971 to commemorate all the men and women who died in pursuit of space travel.

TV camera left on the moonNASA"Hey guys, we gonna need this TV camera?" "Nah, let's just leave it here."

Multiple other discarded objects have been left by visiting astronauts. At the Apollo 11 landing site, called Tranquility Base because of its location within the moon's "Sea of Tranquility," more than 100 items have been left. These include: Two pairs of space boots (Neil Armstrong's and Buzz Aldrin's); empty food bags and storage containers; multiple cameras and leftover film; multiple tools; and even "defecation collection devices" and "urine collection assemblies" (aka astronaut toilets, which still contain deposits made by Neil Armstrong).

While some of these things sound unless and even gross, a group called the Lunar Legacy Project are working to preserve the site. From a recent BoingBoing article:

While bags of frozen astronaut poop may sound unimportant, even a little gross, some "extreme heritage" conservationists are very concerned about their protection — as well as the other detritus left behind by humanity's first moon walkers. For now, Tranquility Base is still tranquil (there is no wind or rain up there to damage things), but preservationists worry that private space enterprises will one day endanger the Apollo landing site, as well as other important landmarks on the moon.

California and New Mexico have added the site to their historical registries, but it isn't a recognized Historical Landmark by the National Parks Service or considered a World Heritage Site by UNESCO.