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Tardigrades, the toughest animals on Earth, have crash-landed on the moon

The tardigrade conquest of the solar system has begun.

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A cartoon tardigrade in space.
“Mwhahahahaah. Our conquest of space has begun.”
Getty Images/iStockphoto

In 1983, a team of Japanese scientists on a journey through Antarctica happened upon a pile of moss harboring a strange, strange creature.

Living in the moss were tardigrades, millimeter-long animals that resembled teddy bears crossed with caterpillars. The tardigrades (sometimes called “water bears”) and the moss they were found in were wrapped in paper, placed in plastic baggies, and locked away in a -4 degrees Fahrenheit freezer. There they remained — frozen and forgotten — for more than 30 years.

This sounds like the start of a horror movie. But rest assured: When scientists thawed the tardigrades in 2014, the microscopic animals did not seek vengeance upon humanity for their imprisonment. Instead, they moseyed around on a plate of agar gel like nothing had happened. And then they reproduced.

Scientists keep learning about tardigrades and their remarkable ability to survive just about anywhere. And they’ve learned that different species of tardigrades have different adaptations for a wide variety of environmental threats.

In hot conditions, they release heat-shock proteins, which prevent other proteins from warping. Some tardigrades can form bubbly cysts around their bodies. Like puffer jackets, the cysts allow them to survive in harsh climates. In dry conditions, they shrink down into a protective pill shape, called a tun. In this state, they can survive — without water, or being trapped in ice — for decades.

Tardigrades live in the ocean and in the soil of every continent, in every climate and in every latitude. Their extreme resilience has allowed them to conquer the entire planet. That’s because tardigrades are one of the toughest — if not the toughest — animals on planet Earth.

And now, as Wired reports, they’ve landed on the moon. And it’s possible they’ll survive even there.

Hold up. Why are tardigrades on the moon?

In April, the lunar lander Beresheet — a privately funded Israeli project — crashed on the moon. The mission originally started as a contender for the Google Lunar X prize, a contest to land a privately made robot on the moon before a 2018 deadline. As The Verge’s Loren Grush explains, it wasn’t a very robust scientific mission: It had planned to run some simple tests on the moon’s magnetism. The mission was more a proof of concept that ambitious space exploration can take place outside of big government programs.

Sadly, the craft crash-landed due to a computer error.

But a part of the mission lives on. A group called the Arch Mission Foundation had installed a library of sorts on the craft, and they tell Wired, they believe it may have survived. Arch Mission has the goal of “maintaining a backup of planet Earth,” and wanted a store of information on the moon “to preserve the records of our civilization for up to billions of years.” In the future, after our extinction, if aliens were to land on the moon and find the archive, they could learn about us (and presumably feel sorry we’re no longer around).

The “library” was etched on to a nickel-metal disc, and it contained nearly all of English Wikipedia, copies of classic books, human blood samples, and tardigrades (because if anything alive on Earth is going to last billions of years, it’s them). Many of those tardigrades are coated in a protective resin, much like how amber preserves long-dead mosquitos that were once trapped in tree sap.

According to Wired, a co-creator of the library believes the disc survived the crash. “In the best-case scenario, Beresheet ejected the Arch Mission Foundation’s lunar library during impact and it lies in one piece somewhere near the crash site,” Wired reports.

It provokes a fascinating question: How long can those tardigrades survive on the moon?

Why Tardigrades are the toughest animals on Earth — and now possibly the moon

It’s important to note: Tardigrades are basically indestructible only when they enter a special state called cryptobiosis. In this state, they tuck in their legs and expel all moisture from their bodies, preserving their bodies. They’re called tuns when they reach this state, and it was tuns that were sent aboard Beresheet.

As tuns, the tardigrades produce glycerol (antifreeze) and secrete trehalose, a simple sugar that mummifies them in a glass suit of armor. This process is called vitrification, and scientists have studied it for use in protecting other delicate cellular tissues like sperm and eggs. As a tun, the tardigrade reduces its metabolism by 99.99 percent as it waits for a more suitable environment.

Tuns are remarkably resilient; they can survive in ice for decades. But they also can survive the harsh conditions of space, at least for a little while.

In 2007, the European Space Agency launched a satellite carrying (among other things), a payload of tardigrades in tun form, and selectively exposed them to the vacuum of space and cosmic radiation. Ten days later, the tardigrades were returned to Earth and rehydrated. Remarkably, a handful of them survived both the radiation and the vacuum, making them the first animals on record to survive complete space exposure.

Research has also shown the tuns can survive pressures up to 87,022.6 pounds per square inch — six times what you’d find in the deepest part of the ocean. (Around 43,00 PSI, “most bacteria and multicellular organisms die,” Nature reported.) They’re that tough.

If a cataclysm wipes out most of life on the planet — including humans — it’s likely that tardigrades will survive.

Why the question of what can survive on the moon is so fascinating

The moon formed more than 4 billion years ago. And for the entirety of its existence, it has been a completely sterile place. Humans first brought life to the moon — in the form of microbes hiding in feces and other human waste — 50 years ago, with the Apollo missions. And now, it has tardigrades too.

It will be fascinating if, one day, astronauts decide to go back and collect them. Because if they can survive on the surface of the moon — an incredibly harsh, irradiated environment — it helps us understand the resiliency of life.

It could also help us investigate the hypothesis that life didn’t start on Earth at all. Rather, perhaps it was seeded by microbes from another world. If life can survive on the moon, even in a dormant state, it could mean that life 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.

That’s a huge question in astrobiology. Maybe these tardigrades, one day, can help us discover the answer.