Humans tend to leave junk wherever we go.

The moon is no exception. It's estimated that we've left nearly 400,000 pounds of stuff on the moon over the course of dozens of human and uncrewed missions.

Most of the objects are simply defunct spacecrafts, probes, and rockets, intentionally crashed into the moon's surface after their missions were over. But there are also a handful of stranger things on the moon: art projects, sporting goods, and even bags of feces.

Here are eight of the weirdest things we've left on the moon so far.

1) 96 bags of urine and feces

During the Apollo missions, astronauts had to poop and pee, just like we all do on Earth. So even though it might sound like a hoax, there really are 96 bags used to collect these body fluids (some full, some empty) sitting around on the moon's surface after all these years — left behind by astronauts to lighten their craft's load, compensating for the lunar rocks they'd brought aboard.

Recently, some astrobiologists have actually gotten interested in possibly looking at this poop, to see if there are any bacteria remaining in the feces and whether they've mutated at elevated rates due to exposure to radiation.

2) 12 pairs of space boots

At the conclusion of Apollo 11, apart from bags of body fluids, Neil Armstrong and Buzz Aldrin also lightened their load by leaving behind about 100 objects they no longer needed. The stash included space boots, cameras, tools, and film.

For more ceremonial purposes, they also left behind the famous US flag they'd planted in the lunar soil (though it was blown over by rocket exhaust when they left), a small gold olive branch pendant, and a ceremonial silicon disc that had been engraved with about 100 goodwill messages from US politicians, NASA administrators, and world heads of state.

3) A plaque signed by Richard Nixon

Nixon was president for all six human missions to the moon, including the first, which astronauts marked by leaving the plaque above on the moon's surface.

So even though Nixon merely inherited the Apollo program just months before the first moon landing — and, of course, would later end his presidency in disgrace (ranking second to last on Vox's ultimate semi-arbitrary ranking of American presidents) — he's the only president who got his signature on the moon.

Well played, Nixon.

4) Artwork by Andy Warhol, Robert Rauschenberg, and Claes Oldenburg

This one's an unconfirmed rumor — but there's reason to believe it might be true.

During the 1960s, sculptor Forrest Myers reportedly had the idea to get six artists to collaborate on a tiny piece of artwork that would be left on the moon, and eventually recruited some big names to draw tiny sketches for what he'd call Moon Museum. The designs — which included a Mickey Mouse-esque drawing by Claes Oldenburg and a stylized sketch of Warhol's initials that look suspiciously like a penis — were shrunken down and etched onto a tiny ceramic wafer by scientists at Bell Labs.

Myers, however, was unable to convince NASA to go along with the plan. So he supposedly convinced an engineer working on the Apollo 12 module to hide the wafer in the gold blanket that surrounds its lower sections.

The engineer, Myers says, smuggled the wafer aboard. And two days after Apollo 12 landed and then left the moon — discarding the module and letting it crash on the lunar surface — Myers revealed his scheme to the New York Times. NASA, though, has never confirmed it.

5) Two golf balls

Alan Shepard famously brought the head of a six-iron golf club on the Apollo 14 mission, attached it to a tool intended to scoop lunar soil, and shagged a few balls.

On a few of the swings, Shepard made pretty solid contact, saying he drove the ball "miles and miles" in the moon's microgravity environment. It was probably more like a few hundred yards, but the bottom line is that he never bothered to go pick up the balls — so there are currently two 1970s-era golf balls still sitting on the moon.

6) A controversial piece of art

Fallen Astronaut is a 3.5-inch abstract aluminum statuette, created by Belgian artist Paul Van Hoeydonck and left on the moon by astronaut David Scott during the Apollo 15 mission.

Scott left it on its side as a memorial, next to a plaque with the names of 14 astronauts who'd died during previous missions. But Van Hoeydonck later objected to the name and said he'd intended for it to be left upright, as a symbol for how humans were using the moon as a stepping stone to the stars.

The disagreement eventually boiled over into a scandal, as Van Hoeydonck sought to sell replicas of the statue (violating his agreement with Scott), before changing his mind. But the original Fallen Astronaut still sits in the same spot on the moon, 43 years later.

7) A falcon feather

Near the end of Apollo 15, Scott carried out a version of the classic feather/ bowling ball experiment, in order to show that in a vacuum, any two objects dropped together will land at the same time.

Scott did it with a hammer and a feather, but the result was the same. At the end, he left the feather — taken from Baggin, the Air Force Academy's falcon mascot — on the moon's surface.

8) A photo of an astronaut's family

During Apollo 16, while using the lunar rover to explore the Descartes Highlands, Charles Duke left this 3-by-5-inch photo of himself, his wife Dorothy, and their sons Charles and Thomas on the ground.

Duke hasn't said why he left the photo, but on the back, he wrote a message to any creature that might come across it: "This is the family of Astronaut Duke from Planet Earth. Landed on the Moon, April, 1972." Unfortunately, the photo is probably quite faded by now, after more than 40 years on the moon's surface.