Share All sharing options for: Apollo astronauts left their poop on the moon. We gotta go back for that shit.

It’s been nearly 50 years since the Apollo 11 moon landing. Neil Armstrong’s iconic footprint is still there, undisturbed; there’s no atmosphere, no wind on the moon to blow it away.

But the bigger human footprint on the moon is, arguably, the 96 bags of human waste left behind by the six Apollo missions that landed there.

Yes, our brave astronauts took dumps on their way to the moon, perhaps even on the moon, and they left behind their diapers in baggies, on humanity’s doorstep to the greater cosmos.

The bags have lingered there, and no one knows what has become of them. Now scientists want to go back, and answer a question that has profound implications for our future explorations of Mars: Is anything alive in them?

Human feces can be disgusting, but they’re also teeming with life. Around 50 percent of their mass is made up of bacteria, representing some of the 1,000-plus species of microbes that live in your gut. In a piece of poop lives a whole wondrous ecosystem.

Planet Earth has hosted this life and so much more for upward of 3.9 billion years. The moon, as far as we know, has been sterile and lifeless that whole time.

With the Apollo 11 moon landing, we took microbial life on Earth to the most extreme environment it has ever been in. Which means the human feces — along with bags of urine, food waste, vomit, and other waste in the bags, which also might contain microbial life — on the moon represents a natural, though unintended, experiment.

The question the experiment will answer: How resilient is life in the face of the brutal environment of the moon? And for that matter, if microbes can survive on the moon, can they survive interstellar travel, making them capable of seeding life across the universe, including on places like Mars?

Wait, astronauts pooped on the moon and just left it there?!

After Neil Armstrong descended from the Eagle lander, becoming the first human to set foot on the moon, the very first picture he took on the surface shows, yes, the moon’s cratered surface, but also a white jettisoned trash bag (or jett bag).

I can’t confirm there are feces in this particular bag (Buzz Aldrin declined to comment for this story), but there’s definitely one like it on the moon that contained or still contains human waste, according to the NASA History Office.

Apollo 16 astronaut Charlie Duke spent 71 hours on the moon in 1972. On a recent phone call, he confirmed that the crew left human waste behind.

“We did,” he says. “We left urine that was collected in a tank ... and I believe we had a couple of bowel movements — but I’m not sure — those were in a trash bag. We had a couple of bags of trash we kicked out on the lunar surface.”

(You might be thinking, “Wait he was on the moon for nearly three days and he’s unsure if he pooped there?” As he told me, “Three days is not bad to have without a bowel movement.” Fair enough?)

Even so, he says, they threw out the garbage thinking everything would be sanitized by the solar radiation. “I’d be really really surprised if anything survived,” he says. Plus, taking it back with them wasn’t really an option.

“The moon missions were engineered very carefully, and weight was a very big issue,” says Andrew Schuerger, a University of Florida space life scientist who recently co-authored a paper on the viability of microbes surviving on the moon. “So it made sense if you’re picking up moon rocks, you’d also want to discard things that were not necessary to increase your margin of safety.”

During the flight to the moon, the astronauts relied on “a plastic bag which was taped to the buttocks to capture feces,” according to NASA. It was a disgusting, cumbersome process.

On the moon itself, the astronauts used a “maximum absorbency garment” for “fecal containment.” But forget the technical phrasing. It’s a diaper.

With the 50th anniversary of the Apollo 11 moon landing on July 20, there’s renewed interest in returning humans to the moon in the near future. The Trump administration has a goal of getting back there by 2028 at the earliest. And there’s budgetary momentum for NASA to work on a “lunar gateway,” a habitable space station that will orbit the moon, allowing for longer-term lunar missions and prep for an eventual human mission to Mars.

As we prepare for those journeys and beyond, the poop is one more reason we have to go back.

The case that the poop bacteria are dead

The question scientists are asking of whether anything is alive in those jett bags, while seemingly silly, may lead to important insights about the extreme conditions life can endure. But it will also speak to our human potential to contaminate celestial bodies — or even seed life on them — when we go exploring. That’s reason enough to go back to the moon and collect some samples.

Those jett bags “are the most protected of anything that would have high levels of fungi, [bacteria], and viruses from Earth,” Schuerger says. (Fungi are another form of microbial life that could possibly have survived.) For astrobiologists, that means those bags are the most interesting objects on the moon.

That said, the chances that anything survived in any of those jett bags are slim, Schuerger says. He and his colleagues recently completed an analysis modeling the likelihood that any microbes from Earth are still alive on any of the surfaces of the spacecraft that were left behind on the moon. The jett bags might be better protected (more on that in a bit), but the same harsh conditions apply.

In all the ways Earth is so hospitable to life, the moon is not. It does not have a protective magnetic field to deflect the most powerful and damaging cosmic radiation. It does not have an ozone layer to absorb the sun’s ultraviolet rays.

The vacuum of the moon is inhospitable to life. And without an atmosphere, the moon is subjected to wild temperature swings over day and night: It can be minus 173 degrees Celsius (minus 279.4 degrees Fahrenheit) at night, and 100°C (212°F, or the boiling point of water on our surface) during the day.

There’s a good chance that a combination of radiation and extreme temperature has killed the microbes in the jett bags. Schuerger says there’s a “low probability” that anything survived in them. “But it’s the highest probability of anything that landed on the moon.”

The case that the poop bacteria are alive

The surface conditions are harsh, but don’t lose hope: “Microbes don’t need to have a lot of protection,” Margaret Race, a biologist at the SETI Institute, says.

After all, bacterial life has been found on Earth just about everywhere we look: at the very bottom of the ocean, near scorching thermal vents, 2 miles beneath one of Greenland’s glaciers. On the Apollo 16 mission, the astronauts performed an experiment where they kept a sample of nine species of microbes on the outside of the spacecraft, exposing them to the harshest conditions in space. Many of them survived (though a few days in space is not the same as 50 years in space).

“We do not have a definition of life that says, ‘It can never go beyond this temperature, beyond this salinity, beyond that acidic level,’” Race says. “Every time we look places, we find life.”

A lot would have to go right for the microbes to still be alive — or at least revivable. Bacteria can’t replicate (i.e., grow) without moisture. The human waste would have to have been packaged really well, for one, so their environment could remain moist. “In the [moist] environment of a closed diaper, presumably you should be able to have replication,” says Mark Lupisella, a NASA scientist who is doing some preliminary work on a potential mission to retrieve the jett bags and study them.

The jett bags would have to still be intact, which is not a given considering the wild temperature swings on the moon; they could be ripped open by the mechanical forces involved with heating and cooling.

“Also, we don’t know what the internal temperature of the bag is going to reach when it’s exposed to the sun,” Schuerger says. If it tops 100°C, he says, bacteria would likely only survive a few days, or weeks, on the moon.

Lupisella says even if all the life in the jett bags is dead, the bags are still worth studying. Scientists could possibly figure out how long the microbes lived on the moon and whether they evolved or adapted to the environment at all. “It’s a stretch, but it is possible we could discern whether or not these life forms might have mutated early on,” he says.

He’s saying there’s a tiny chance that natural selection might have kicked in inside those jett bags, leading to the microorganisms evolving to survive. If there were just a few microorganisms in the poop with the ability to survive the moon, they could have grown and spread.

Again, this is the most extreme place we’ve ever left life — possibly the most extreme place life has ever been. We need to see how resilient (or not) it is in that environment.

There’s also the possibility that some microbes might be revivable. That is, after decades of dormancy on the moon, some of these microbes might be able to be coaxed back to life under the right conditions. Bacterial spores (dormant bacteria that form a protective outer coating) in the Arctic have been revived after thousands of years frozen in ice. It would be fascinating if spores in fecal matter could be revived after decades on the moon.

Those lessons would be interesting for microbiology — assessing the extreme limits for microbial life — but they’d be invaluable for a trip to Mars.

The moon poop matters for future missions to Mars

If microbes can survive for a given period on the moon, they’re even more likely to survive on Mars, which has a thin atmosphere, a more hospitable environment, and evidence of flowing water.

One of scientists’ top questions about Mars is, “Is there, or has there ever been, life here?” The prevailing wisdom is that if life exists there, it probably looks a lot like bacteria, or some other type of very simple single-celled organism.

But if we make it to Mars and then accidentally contaminate the planet with our literal shit, it might be harder to answer this question. How would we know if the life we find on Mars is truly Martian, or something that’s come from Earth? And if our microbes from Earth take a liking to Mars and spread, there may be no way to undo that.

The UN Outer Space Treaty — signed in 1967, two years before the Apollo 11 landing — stipulates that member states “shall avoid harmful contamination of space and celestial bodies.” That may be difficult if we get to Mars because wherever we go, our fecal matter goes too.

Thinking about poop on the moon helps us think about a possible origin of life on Earth

As new missions to the moon are planned, we need to think carefully about the need to preserve the artifacts left at the Apollo landing sites. NPR’s Nell Greenfieldboyce recently reported that just landing within 100 meters of an Apollo site could potentially damage it.

Protecting the history of human exploration on the moon also means protecting the garbage — its historic value is immense, but so is its scientific value. We need to preserve these sites so scientists can return to them and take samples.

For me, knowing there are intact bags of human waste on the moon provides fuel to the furnace of my imagination. For instance, consider the hypothesis that life didn’t start at Earth at all. Rather, perhaps it was seeded by microbes from another world.

Now let’s say an asteroid comes hurtling by, slams into the moon, and projects the Apollo mission poop into the deep reaches of space (an extremely hypothetical situation). Could that seed life in the broader universe? Maybe.

And in that case, could life on Earth have been seeded by some alien astronaut’s feces? “No prevailing theory I’m aware of involves an astronaut’s diaper, but that whole idea is perfectly scientifically plausible,” Lupisella says.

Related How Apollo moon rocks reveal the epic history of the cosmos

If microbial life can survive on the moon, even in a dormant state, it could mean that microbes can survive long stretches of time in the deep reaches of space, traveling between worlds, propagating life along the way.

“Can simple life spread through the cosmos like radio waves [just naturally moving through the universe, on its own], or does it need to wait billions of years until there are technological species with spaceships to spread it?” planetary scientist Phil Metzger recently asked on Twitter. “This is just one of the MANY important scientific questions we will try to answer when we get back to the Moon.”

Life is a precious miracle — even the life contained in our feces. Let’s stand in awe of the fact that some of it might be alive on the moon. It would mean life seeded on a dead world, however small.

Graphics by Javier Zarracina/Vox