Tardigrades are microscopic animals blessed with two very cool nicknames — the water bear and the moss piglet. They are segmented and reach a maximum length of a millimeter, maybe a millimeter and a half.
Water bears are as seemingly indestructible as they are tiny. They've been known to survive in extreme temperatures, though there are limits. (We'll get to that in a minute.) They shrug off extreme doses of radiation and laugh in the face of the silent vacuum of space itself. In one experiment, water bears were exposed to outer space for 10 days. After returning to Earth, it was discovered that many of the bears had survived and some even had babies.
Scientists even tried to rid the planet of tardigrades (only in theory) by putting the creatures through a series of tests that mimicked what they would experience if a deadly asteroid or radiation burst hit the Earth. But the tardigrades shrugged that off, too, outlasting billions of years worth of theoretic disaster events, according to a study published in the journal Scientific Reports.
Called "Earth's hardiest animals," these resilient creatures have long been the subject of scientific curiosity because they keep surprising us with their ability to bounce back from catastrophe.
They may be alive on the moon
The moon has craters and mountains and other nooks and crannies where tardigrades could survive. (Photo: NASA's Goddard Space Flight Center Scientific Visualization Studio [CC BY 2.0]/Flickr)
Most recently, the little-water-bears-that-could caught our attention because they were revealed to be the only possible survivors from a 2019 crash landing on the moon. Luckily, the Israeli Beresheet probe didn't have any other living cargo on board when it crashed in April — a failed attempt to become the first private spacecraft to land on the moon.
However, a few thousand of the creatures were onboard at the time. They were part of a tiny lunar library put together by the Arch Mission Foundation, a group whose goal is to find a backup for Earth. The library consisted of the tardigrades, 30 million pages of information and human DNA samples.
As founder Nova Spivack told Wired, "Ironically, our payload may be the only surviving thing from that mission."
That doesn't mean they're crawling around up there. But because they can survive the vacuum of space, it just means that if they survived impact, they will remain in a dehydrated, coma-like state from which they can awaken.
They can survive without water
Despite their nickname, water bears (you can watch one wiggle in the video above) can go without water for about 10 years, living as a dried-out shell. For 250 years, we had no idea how these tiny creatures survived this extreme drying out, but a group of researchers from University of North Carolina at Chapel Hill discovered an answer.
Researchers dried out tardigrades to see which genes turned on as a response to the stress, according to their study published in Molecular Cell. Researchers found that intrinsically disordered proteins (IDPs) kicked into gear, filling up the tardigrades' cells with an "amorphous matrix" that prevents them from going completely dry and dying.
IDPs are a little odd. Most proteins are stable and structured, but IDPs are, as their name might suggest, a little looser. They don't have a set shape. Thomas Boothby, the lead author on the study, described them to NPR as "wiggly spaghetti springs where they are constantly changing shape." This shape-shifting allows them wiggle into and keep cells together, creating that previously mentioned matrix of protection.
Boothby and the other researchers then took the tardigrade IDPs and to see if yeast and bacteria would get the same desiccation protection. Some bacteria and yeast survived desiccation by 100-fold. Given that, things like drugs that need to remain cold during shipments or crops in drought-prone areas, may similarly benefit from the tardigrade IDPs.
They can shrug off extreme temperatures, but ...
As mentioned earlier, these microscopic creatures that live on lichen and moss don't skip a beat when faced with cold temperatures. According to Smithsonian, they can survive extreme temperatures, frozen at minus 328 degrees Fahrenheit (minus 200 degrees Celsius) or heated to more than 300 degrees Fahrenheit (roughly 149 C). As with the other catastrophic conditions already mentioned, the secret is that under unfavorable conditions, they go into a state of suspended animation called the "tun" state. As a result, they can live almost anywhere, from Antarctica to the rainforest.
But that super power only gets them so far, as researchers at University of Copenhagen's biology department recently discovered. By looking at the creatures in both active and desiccated states, they realized that tardigrades are indeed vulnerable to long-term high temperature exposures.
The median lethal temperature (meaning 50% of the specimens died) for non-acclimated active tardigrades was 37.1 degrees Celsius (98.7 degrees F). For desiccated specimens, the estimated median lethal temperature was 82.7 C (180.86 F) following a one-hour exposure, though there was a significant decrease to 63.1 C (145.58 F) following a 24-hour exposure. The research was published in Scientific Reports.
"From this study, we can conclude that active tardigrades are vulnerable to high temperatures, though it seems that these critters would be able to acclimatize to increasing temperatures in their natural habitat," explains lead author Ricardo Neves in a news release published on EurekaAlert. "Desiccated tardigrades are much more resilient and can endure temperatures much higher than those endured by active tardigrades. However, exposure-time is clearly a limiting factor that constrains their tolerance to high temperatures."
It's a telling point that these creatures share the same vulnerability to climate change as all other animals on the planet.
They can resist radiation
It was a team of Japanese researchers who figured out the secret behind the hardy critter's amazing defense against radiation. (Other researchers learned that one group of water bears could survive radiation doses of 5,000 to 6,000 grays, or absorbed energy per unit mass of tissue. In contrast, humans would barely survive a dose of 5 grays!) Among the animal's many coping strategies is a protein that protects its DNA from radiation damage. The researchers named it "Dsup" (short for "damage suppressor"). When the scientists transplanted the Dsup protein into human cells in the lab, it protected those cells, too.
The scientists, whose work was published in the journal Nature Communications, suggest that genes from these "extremeophiles" could one day be used to protect humans from radiation. Interestingly, the tardigrades were more resistant to radiation than the human cells with the added Dsup protein.
Subsequent research has built on these findings, unraveling how this protective behavior works. Scientists at University of California San Diego looked at the biochemical makeup of the Dsup proteins and found that Dsup binds to chromatin, which is a mixture of DNA and proteins that forms chromosomes within the nucleus of cells. Once bound to chromatin, Dsup protects cells by forming a shield that protects the DNA from the hydroxyl radicals produced by X-rays, according to a UC San Diego press release.
"... tardigrades have other tricks up their sleeves, which we have yet to identify," Professor Matthew Cobb from the University of Manchester, who was not involved with these studies, told the BBC. In principle, "these genes could even help us bioengineer organisms to survive in extremely hostile environments, such as on the surface of Mars — [perhaps] as part of a terra-forming project to make the planet hospitable for humans."
Editor's note: This story has been updated with new information since it was first published in September 2011.