Tardigrades are some of the toughest lifeforms ever discovered, and it’s been proposed that they (or similar organisms) could seed life through the cosmos by hitching rides on asteroids. Now, researchers at the University of Kent have tested the hypothesis by firing tardigrades from a gas gun into sand, and checking how well they survived.
Tardigrades are microscopic animals that are famously hardy. When faced with a harsh environment, they dry up and curl into a protective ball called a tun, allowing them to survive until conditions become more hospitable again. Doing this, they’ve been seen to survive boiling and freezing temperatures, intense radiation, crushing pressures like those at the bottom of the deep seas, and even jaunts into space.
With this laundry list of superpowers under their belt, tardigrades have been seen as candidates for panspermia, a hypothesis that suggests life could jump between planets and moons by way of asteroids. So for the new study, the Kent researchers investigated how well tardigrades could survive the shock pressures that asteroid impacts would produce – by firing them out of a gun.
First the team froze samples of tardigrades for 48 hours, which made them take on their protective tun form. Then, they loaded the samples into a nylon casing, and fired that out of a light gas gun into sand. Impact speeds and shock pressure were measured, and the tardigrades were collected to inspect any damage they’d taken.
The researchers identified the upper limit of their survival in this scenario – impact speeds of 3,240 km/h (2,013 mph), which creates a pressure shock of 1.14 Gigapascals (GPa). The fastest speed at which 100 percent of the tardigrades survived was 2,621 km/h (1,628 mph), while about 60 percent continued to survive impacts up to 2,970 km/h (1,845 mph).
That said, the survivors seemed a little worse for wear. The team noticed that it took them up to 36 hours to come out of their tun state and start moving again – much longer than a control group that was frozen and then thawed but not fired out of the gun, which recovered within eight or nine hours.
This finding has implications for panspermia. The team says that the majority of impacts by asteroids would create pressures too high for tardigrades to survive, but a fraction of them occur slower, within the range of tolerance. Up to a third of asteroid strikes on the Moon, for example, would be survivable by tardigrades – something that we may have already inadvertently tested with the crash of the Beresheet lander in 2019, which was carrying frozen tardigrades. How well they’d fare once there is another question.
Interestingly, the team also says these findings could be used to test whether tardigrades, or other similar lifeforms, are already living on other worlds in our solar system. The icy moons Europa and Enceladus have subsurface oceans that are potentially habitable by microorganisms, and we could find evidence of life by checking the plumes of water they vent into space through cracks in the icy shell.
Cassini has already collected material by flying through these plumes, but its speeds would have been lethal by tardigrade standards. The researchers say that catching materials using thick aerogels as a softer landing surface could lessen the shock pressure and keep any potential alien tardigrades alive.
Of course, this is all speculative at the moment, but the study does show that panspermia is plausible under some circumstances. The team says that further investigation should include checking how viable the survivors are, and whether tardigrade eggs can handle faster impacts.
The research was published in the journal Astrobiology.