The microscopic tardigrade—also known as the water bear—is the only animal that can survive the cold, irradiated vacuum of outer space. Here’s what makes these little guys so amazing.
Tardigrades are one of the most fascinating creatures on Earth—and now, the moon, too. The mysterious microscopic critters have landed on the lunar surface in what sounds like the beginning of a sci-fi thriller. But they’re not there as part of a hostile takeover. They’re there completely by accident.
Back in April, the moon-bound Israeli spacecraft Beresheet crashed due to a computer error. Scientists loaded the tardigrades onto the Beresheet along with human DNA samples; when the lunar lander crashed, thousands of dehydrated tardigrades might have spilled onto the moon’s surface, according to a WIRED report.
The tardigrades were in “tun” form, a dormant state where they shrivel up into a ball, expel most of the water in their bodies, and lower their metabolism via cryptobiosis until they enter an environment better suited to sustain life. They can exist like this for decades. They’re also pretty hardy and can endure the harshest environments, including subzero temperatures—and the recent crash landing.
“Tardigrades can survive pressures that are comparable to those created when asteroids strike Earth, so a small crash like this is nothing to them,” Lukasz Kaczmarek, an expert on tardigrades, told The Guardian.
So what does this mean for humanity? That depends on what the research produces. If humans can replicate cryptobiosis in the way tardigrades do, we’d live far longer than the average life expectancy of 78.7 years for Americans.
According to Kaczmarek, when a tardigrade enters the tun state, it doesn’t age. It becomes dormant at one month old and can wake up years later and still biologically be the same age.
“It may be that we can use this in the future if we plan missions to different planets, because we will need to be young when we get there,” said Kaczmarek.
Until then, here’s everything you need to know about these weird, wonderful creatures.
What’s so special about tardigrades?
Tardigrades are a class of microscopic animals with eight limbs and a strange, alien-like behavior. William Miller, a leading tardigrade researcher at Baker University, says they are remarkably abundant. Hundreds of species “are found across the seven continents; everywhere from the highest mountain to the lowest sea,” he says. “Many species of tardigrades live in water, but on land, you find them almost everywhere there’s moss or lichen.”
In 2007, scientists discovered that these microscopic critters can survive an extended stay in the cold, irradiated vacuum of outer space. A European team of researchers sent a group of living tardigrades to orbit the earth on the outside of a FOTON-M3 rocket for 10 days. When the water bears returned to Earth, the scientists discovered that 68 percent lived through the ordeal.
Wait, what? How is that possible?
Although (as far as we know) tardigrades are unique in their ability to survive in space, Miller insists that there is no reason to believe they evolved for this reason or—as a misleading VICE documentary has implied—that they are of extraterrestrial origin. Rather, the tardigrade’s space-surviving ability is the result of a strange response they’ve evolved to overcome an earthly life-threatening problem: a water shortage.
Land-dwelling tardigrades can be found in some of the driest places on earth. “I’ve collected living tardigrades from under a rock in the Sinai desert, in a part of the desert that hadn’t had any record of rain for the previous 25 years,” Miller says. Yet these are technically aquatic creatures, and require a thin layer of water to do pretty much anything, including eating, having sex, or moving around. Without water, they’re about as lively as a beached dolphin.
But land-dwelling tardigrades have evolved a bizarre solution to living through drought: When their environment dries up, so do they. Tardigrades will enter a state called desiccation, in which they shrivel up—losing all but around 3 percent of their body’s water and slowing their metabolism down to an astonishing 0.01 percent of its normal speed. In this state, the tardigrade just persists, doing nothing, until it’s inundated with water again. When that happens, the creature pops back to life like a re-wetted sponge and continues onward as if nothing had happened.
What’s even more astonishing is that tardigrades can survive being in this strange state for more a decade. According to Miller, a few researchers believe some species of tardigrades might even be able to survive desiccation for up to a century. Yet the average lifespan of a (continuously hydrated) tardigrade is rarely longer than a few months.
“It sounds quite strange,” says Miller, “that even though these tardigrades only live for a few weeks or months, that lifetime can be stretched over many, many years.”
How does being dried out protect them from the vacuum of space?
In its desiccated state, the tardigrade is ridiculously, almost absurdly resilient. Laboratory tests have shown that tardigrades can endure both an utter vacuum and intense pressures more than five times as punishing as those in the deepest ocean. Even temperatures up to 300 degrees Fahrenheit and as low as -458 degrees F (just above absolute zero) won’t spell the creature’s doom.
But the exact source of its resilience is a mystery, says Emma Perry, a leading tardigrade researcher at Unity College in Maine. “In general, we know very little about how this species functions, especially when we’re talking about the molecular level.”
There are clues. Scientists have learned that when the tardigrade enters its desiccated state, “it replaces some of its cell contents with a sugar molecule called trehalose,” Perry says. Researchers believe this trehalose molecule not only replaces water, but also in some cases can physically constrain the critter’s remaining water molecules, keeping them from rapidly expanding when faced with hot and cold temperatures. This is important, because expanding water molecules (like what happens when you get frostbite) can mean instant cellular death for most animals.
What about space radiation?
Space is deadly, and not just because of the vacuum. Outside our protective atmosphere there is killer radiation caused by distant supernovae, our sun, and other sources. Space radiation comes in the form of harmful charged particles that can imbed in the body of animals, ripping apart molecules and damaging DNA faster than it can be repaired.
But here, too, the tardigrade seems oddly prepared for life in space. According to Peter Guida, the head of NASA’s space radiation laboratory, one of the biggest radiation concerns for astronauts (and space-bound tardigrades) is a set of molecules called reactive oxygen species. Ionizing radiation enters the body and bores into wayward molecules that contain oxygen. In simple terms, those newly irradiated molecules then troll through the body causing all sorts of harm.
Tardigrades during their desiccated state produce an abnormal amount of anti-oxidants (yes, these actually exist outside the health-food world), which effectively neutralize those roaming, evil reactive oxygen species. Partly because of this talent, tardigrades have been found to withstand higher radiation doses with far greater success than researchers would otherwise believe they should.
The reason that tardigrades would have evolved to survive high radiation doses is a mystery, too. However, Miller points to a leading theory: Perhaps tardigrades evolved to be swept up by the wind and survive in the earth’s atmosphere—which would explain not only their hardiness but also that they’re found the world over.
However it happened, there’s still much, much more to learn about these fascinating creatures.
This article was written by William Herkewitz and Daisy Hernandez and was published by Popular Mechanics on 07/08/2019