A laboratory experiment suggests that tardigrades, known for their extreme ruggedness, would struggle to survive an asteroid impact on Earth. This study, which has some limitations, directly echoes the theory of panspermia which suggests that terrestrial organisms are the result of extraterrestrial “contamination”.
The tardigrades, very resistant creatures
Tardigrades are often considered the hardiest creatures on the planet. And for good reason, these small invertebrates (around 1,300 recorded species) are known to withstand temperatures as low as -272 ° C, while others can survive for many years without water or oxygen. Some species can also endure the vacuum of space, while others acclimatize to overwhelming ocean pressures.
As show from new research in astrobiology, tardigrades would also be able to survive impacts at high speed… but only up to a point.
As part of this work, a team led by Alejandra Traspas, Queen Mary University, London, attempted to assess the ability of tardigrades to survive extreme impact shocks, and associated pressures. This study aimed to testing the hypothesis of panspermia, the unproven idea that alien microbes can “contaminate” a lifeless world.
For this experiment, the researchers recruited about twenty tardigrades of the species Hypsibius of the garden. After a meal of mineral water and moss, they were placed in hibernation. Then groups of two to three individuals were placed in wells filled with water placed inside a nylon cylinder. The researchers then used a two-stage, lightweight gas pistol to fire at it. In total, six shots were fired at speeds ranging from 556 to 1000 m / s.
At the same time, a control group of about twenty tardigrades was also frozen, then resuscitated without having been shot. All of them survived.
After analyzes of the “victims”, it emerged that some tardigrades had indeed survived the shootings. can go up to 900 m / s and generate 1.14 GPa of pressure. Beyond that, however, “only fragments of tardigrades were recovered“, Can we read in the study. In other words, all creatures have been pulverized.
In view of these results, it would therefore be highly improbable according to the authors that these small animals, hitchhiking on an asteroid, could survive an impact on a planetary body, stressing that these speeds and pressures are “typical of impacts that occur naturally in the Solar System“.
Complicated, but not impossible
In contrast, researchers do indeed agree that creatures attached to asteroids could experience lower shock pressures by being nestled deep inside, for example.
Moreover, remember that in 2019, the Israeli probe Beresheet, which carried a batch of tardigrades on board, had accidentally crashed on the lunar surface. at speeds up to 140 m / s. In other words, below the threshold of destruction of tardigrades recorded in this new study. A question then arises: could they have survived the impact? It’s possible. However, unless we go straight there to see, we’ll probably never know.
Finally, even if this experience does not necessarily go in the direction of panspermia, let us underline that it is limited only to tardigrades, and to a single species. It is thus conceivable that other organisms, such as simple microbes similar to bacteria, are able to resist greater stressors.