Yesterday marked 46 years since Apollo 11 astronauts Neil Armstrong and Buzz Aldrin took their first steps on the lunar surface, following a harrowing landing. It also marks another historic milestone, one that represents a messier side of the exploratory spirit that propelled astronauts to the moon. Forty-six years ago, humankind first took out the trash on another world.

Forty-six years ago, humankind first took out the trash on another world.

Approximately five minutes before Armstrong took his first historic step, he and Aldrin undertook some housekeeping familiar to all Americans. Aldrin handed Armstrong a white bag known as a "jettison bag," or "jett bag" for short, full of things the astronauts no longer needed–the banal detritus of spaceflight, from food wrappers to containers of human waste. Armstrong dropped the jett bag to the surface and later kicked it under the lunar module to get it out of the way. Like the garbage we throw away on Earth, however, it didn't just magically disappear. The first photograph that Neil Armstrong took during his historic moonwalk featured the garbage bag prominently in the foreground.

In recent years, space junk has become a hot topic—it was even the villain in a Hollywood movie. But old satellites, empty rockets, spare space suit gloves, and other accidental byproducts of the space industry aren't the only ways that humankind has cluttered our cosmic neighborhood. As evidenced by the Apollo 11 jett bag, we also throw out space junk on purpose. Other Apollo missions left garbage bags on the lunar surface, and the Apollo 16 astronauts even tossed one overboard on their trip back to Earth, sending off an accumulation of urine bags, peaches, and other junk with a fond "bye bye, bag!"

Lest we chalk this up to an earlier, less-green moment in history, astronauts and cosmonauts today continue to practice what amounts to littering in space. Everything from discarded scientific equipment to old spacesuits gets tossed overboard with the expectation that these objects will eventually reenter the atmosphere and burn up. Since the mid-1960s the Department of Defense has documented several hundred garbage bags thrown out by space travelers, mostly by cosmonauts. The majority reentered as expected, though some circled the planet for years before falling back to Earth.

A future extraterrestrial archeologist may find an artifact even more valuable than our aging space probes and golden records: the lucky ones will find our garbage.

As we celebrate one of the most exciting moments in human history, don't let the presence of the jett bag in Armstrong's photo get you down. Humankind has sent incredible technological emissaries into the cosmos, with the New Horizons Pluto probe recently joining its esteemed predecessors on a path out of the solar system. Some of us have speculated what intelligent aliens might be able to decipher about humanity should they stumble upon these spacecraft. However, a future extraterrestrial archeologist may find artifacts even more valuable than our aging space probes and golden records: the lucky ones will find our garbage. By looking at what we threw away, they may get a much more accurate picture of how our species lived.

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