TWH – In the 1993 Steven Spielberg film Jurassic Park, based on the book by Michael Crichton, the hipster scientist Ian Malcolm, played by Jeff Goldblum, famously spoke to the tenacity and adaptability of life on earth. “Life breaks free,” he says. “It crashes through barriers, painfully, maybe even dangerously, but… Life finds a way.”
Meet one hero personifying that statement: the tardigrade, also known as the water bear, or, perhaps more adorably, as moss piglets. Besides being extremely cute, this microscopic creature could be the avatar of resilience. One recent study in the journal Astrobiology went about testing their hardiness.
Tardigrades (commonly known as waterbears or moss piglets) – [Image credit: Frank Fox]
Before getting to the new study, we should get to know these little beasts. If the Bull of Heaven had been anything like them, the Epic of Gilgamesh might have a different ending. To call them hardy is an understatement.
Tardigrades are pudgy, eight-legged water-dwelling micro-animals that were first described in 1773. Their name means “slow steppers.” Their bodies are segmented with four legs, and they have a flea-like appearance. At their largest, they are only about half a millimeter long.
They feed on algae, plant cells, and microscopic invertebrates with a suction-like mouth. They have lobed brains and, weirdly, all adults of the same species have the same number of cells. Though minute, they can be viewed under low-powered microscopes.
The fossil record suggests that the earliest members of the tardigrade family, which contains some 1,300 species, evolved into its modern form 145 million years ago.
Tardigrades are also stunningly hardy. They are ubiquitous on Earth. They have survived all five mass extinction events on Earth – and that’s really just the beginning.
Mountaintops? Deep-sea vents? No problem. Some can handle 6,000 atmospheres of pressure, six times the deepest ocean pressures found on Earth. They have been found in an Antarctic lake almost a mile underground.
Mud volcanoes? Please. As long as the temperature is below 304 °F (about 151 °C), they will be fine.
At the other end of the temperature spectrum, they can handle temperatures below −328 °F (−200 °C) for a few days. They do have some limits; they can only take temperatures close to absolute zero like −458 °F (−272 °C) for a few minutes.
They can survive up to 30 years without food, and just as long without water. They can enter a dehydrated state, and need water to remain active, not to stay alive.
They can also go without oxygen: tardigrades can survive air deprivation, extreme pressures, and even the vacuum of space. During the FOTON-M3 mission in 2007, dehydrated tardigrades were exposed to hard vacuum and solar radiation, then returned to Earth. 68% of them survived.
Tardigrades can withstand 1,000 times more radiation than other animals. They appear to have something scientists call “Dsup,” a “bizarre protective protein they evolved that somehow shields their DNA from radiation damage,” according to New Scientist. “Short for ‘damage suppressor,’ Dsup appears to work by physically cuddling up to DNA and cocooning it from harm, but without disrupting its normal functions.”
In late 2020, a new species of tardigrade was discovered that created a fluorescent shield to protect itself from UV radiation described as so lethal that it killed all viruses and bacteria within minutes. Most tardigrades died after 24 hours of constant exposure. But the new species just glowed. Even at 4,000 times the dose, 60% lived on for more than thirty days of exposure. They transformed the dangerous UV light into a harmless blue glow.
Recent research may have found a physical limit for the water bears, however. In 2019, an Israeli spacecraft carrying tardigrades for an experiment crash-landed on the moon due to a computer glitch. By all previous findings regarding their hardiness, they were presumed to survive.
Two researchers at the Centre for Astrophysics and Planetary Science at the University of Kent were not so sure. To test their hypotheses, they fired canisters full of frozen tardigrades from high-speed guns. They found that tardigrades could survive impacts from speeds under 2,000 miles per hour (900 kilometers per second), but anything faster and the water bears didn’t make it.
“They just mush,” one of the researchers said in an interview with Science. The research confirms that the tardigrades aboard the Israeli spacecraft entered eternity.
The purpose of the paper was not about discovering how to kill a water bear, or even about their surviving in the crash. Instead, the research has implications for the theory of panspermia.
The term panspermia originates in the work of the Pre-Socratic Greek philosopher Anaxagoras, who wrote around 500 BCE. He introduced the concept of the nous, or cosmic mind, as an ordering force in the cosmos. He also deduced a correct explanation for eclipses and suggested that eventually, a piece of the sun would be witnessed hurling out of it and toward Earth.
In the 1970s, after a century-long development of scientific conjecture, astronomers Fred Hoyle and Chandra Wickramasinghe proposed that interstellar dust was predominantly organic. That hypothesis was correct. Subsequent hypotheses led to the speculation the life may find a means to cross interstellar space.
“Life could spread from planet to planet or from stellar system to stellar system, carried on meteors,” the famous astrophysicist Stephen Hawking once commented.
Attention then turned to the hardiness of tardigrades, and the current research exposes their limits.
The current findings may show that the tardigrades did not survive the moon crash, but that they “can survive low-to moderate-speed impacts.”
The research does not confirm the panspermia conjecture. But it does suggest that more research is needed, because while most meteor impacts greatly exceed the pressures at which tardigrades can survive, there may still be portions of the collision with pressures within the survivability zone. As the researchers note, “there are niche environments where such transfers may be possible.”
There are still obstacles and questions about interstellar survival of life on pieces of meteors or chunks of planets hurled into space. Among the questions is what these animals would do after the crash.
The research does demonstrate that panspermia is unlikely but possible, given what we already know about the hardiness of tardigrades. The research also opens the possibility that samples from some planetary moons within our solar system could be sampled for life because they are under the speed at which tardigrades can survive.
“it may be possible to successfully sample the plumes of Europa and Enceladus for such life-forms,” the researchers note.
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