The plan was simple: preserve a 30-million-page archive of human history by depositing it on the surface of the moon.
On April 11, 2019, an Israeli spacecraft attempted to land on the moon with a DVD-sized “lunar library” that contained as much human knowledge as possible engraved via high-res images at nano-scale in nickel, including most of the English language Wikipedia. Unfortunately, contact with the lunar lander containing the archive was lost as it was preparing to land. The archive is thought to have survived the crash. Far less concerning, however, are the fates of the spacecraft’s living occupants.
Thousands of tardigrades are now strewn across the surface of the moon. Not to worry, though. These microscopic creatures are virtually indestructible once they enter a dormant state, which was likely triggered by the vacuum of space. Their metabolic processes have stopped, their cells have turned to glass, and they await the day that they will be revived. In the meantime, we’ll be taking a closer look at the tardigrade and why its survivability is such an important topic in the field of microbiology.
The Water Bear
Tardigrades are microscopic, ranging from 100 to 1,000 microns in size. Their round heads, plump bodies and clawed limbs have given rise to the nickname “water bear.” Another nickname is moss piglet, given that tardigrades thrive in damp mosses. However, they have been observed in a number of habitats, not all of which are hospitable.
Tardigrades belong to a remarkable group of microorganisms known as extremophiles. Extremophiles, primarily bacteria and archaea, are organisms able to thrive in harsh environments ill-suited for life, such as hydrothermal vents and acidic hot springs. The suffix phile even means “one who loves.” Yet tardigrades hold a special place even among this niche group. Known as polyextremophiles, they are able to survive in environments with multiple forms of stress.
What makes tardigrades practically indestructible? Tardigrades require a thin layer of water around their bodies to remain active. Environmental stressors trigger cryptobiosis, a reversible state in which organisms suspend their metabolism. Tardigrades squeeze water from their bodies and roll into lifeless balls, known as tuns. Hibernating tardigrades are able to survive without food and water for decades, waiting for conditions to change.
Boiling hot days and freezing nights are of no consequence to tardigrades on the moon, and the vacuum of space merely imposes dehydration. Dormant tardigrades are capable of surviving temperatures from 151 degrees Celsius (303 degrees Fahrenheit) to minus 272 degrees Celsius (minus 457 degrees Fahrenheit). When hibernating, they can survive exposure to X-rays, gamma rays and pressures of 6,000 atm (standard atmosphere). By comparison, the crushing pressures exerted in the Mariana Trench, the deepest location on Earth, is 1,070 atm.
The Origins of Life
Encountering microscopic organisms with a deluge of natural defenses, scientists were compelled to test their limits, so they fired them from a cannon. In a study of tardigrade survival limits in high-speed impacts, researchers loaded a nylon bullet with the species Hypsibius dujardini and fired them out of a two-stage light gas gun at sand targets in a vacuum chamber. They found that tardigrades are able to survive impacts of up to 900 meters per second, but not without damage. Tardigrades sustained internal damage caused by shock, and it’s unclear whether they would be able to reproduce.
The reason for firing tardigrades from a cannon (other than curiosity) is to test the theory of panspermia, which posits that life on Earth sprung from microorganisms delivered via meteorite or comet from a distant planet. A tardigrade surviving the shock of a simulated meteorite impact would lend credence to the theory. “If they could do it and they’re the hardest thing we know, right? Maybe other things can,” said Mark Burchell, a professor of space science and supervisor on the experiment. “[B]ut if they can’t do it, and they’re the hardest thing we know, then maybe nothing else can either.”
Transfer of tardigrades to Earth via meteorite is unlikely, given that they would encounter high shock pressures. Researchers theorized, however, that niche environments in the solar system could make transfer possible. A frozen comet hurtling through space could contain an indestructible microorganism resembling an adorable, miniature bear.
Explore Microorganisms at UF
Extraterrestrial life may one day be found buried beneath the surface of Mars or hidden in the frozen oceans of Europa. A discovery of this magnitude could drastically alter how humanity understands the origins of life and the physical processes necessary for its development, which is why studying the tardigrade’s survivability is so important.
The University of Florida offers a Master of Science in Microbiology & Cell Science with a concentration in Medical Microbiology and Biochemistry and a Graduate Certificate in Environmental Microbiology. Entirely online, these programs focus on small organisms with a big impact on the world around us. If you’d like to dive deeper, we recommend the following courses, both available to all online microbiology graduate students:
- Astrobiology (MCB 5705): An examination of life in our solar system. Offered in the spring, this course focuses on planetary habitability; microbial adaptation to extreme conditions; and planet, star and biosphere formation.
- Prokaryotic Diversity (MCB 6151): An introduction to the diversity of bacteria and archaea, including their origins and evolution, morphological, metabolic and molecular characteristics, genetic and physiology diversity, importance in human, animal and plant health and their roles in elemental cycling.
Tardigrades are fascinating creatures, capable of surviving extreme temperatures, pressures and radiation. Yet their significance goes far beyond their ability to be shot out of a cannon or crash land on the moon. Much of how extremophiles are able to survive and even thrive where other organisms would perish is unknown. The world needs inquisitive microbiologists capable of unlocking the mysteries of indestructible microorganisms.
If you’re interested in studying microorganisms and their influence on humanity’s past, present and future, apply to one of our online microbiology programs.