Tardigrades survived the raw vacuum of open space and came back to life once they were rehydrated

Tardigrades, popularly known as water bears or moss piglets, are microscopic invertebrates rarely longer than half a millimeter that live in mosses, lichens, leaf litter, and the thin films of water that coat soil and sediment nearly everywhere on the planet. Despite looking soft and clumsy under a microscope, with eight stubby legs and a rolling gait, these animals rank among the toughest creatures known to biology. Their extraordinary resilience was demonstrated most dramatically in 2007, when scientists sent live tardigrades into orbit and exposed them directly to the vacuum of open space.

Shutting Down Into a Tun

The secret to tardigrade survival is a process called cryptobiosis, in which the animal expels nearly all of the water from its cells, curls into a compact, barrel-shaped form known as a tun, and drops its metabolic activity to a level too low to measure. In this state a tardigrade is not quite dead and not quite alive; biological processes essentially pause rather than continue at a slower pace. A tun can persist for years, and in some documented cases for decades, waiting for moisture to return before the animal rehydrates and resumes normal activity within hours.

The FOTON-M3 Space Experiment

In September 2007, the European Space Agency’s FOTON-M3 mission carried tardigrades into low Earth orbit as part of an experiment known as TARDIS, short for Tardigrades in Space. Researchers loaded desiccated specimens of two species, Richtersius coronifer and Milnesium tardigradum, onto the outside of the spacecraft and exposed separate groups to different combinations of the vacuum of space, solar and cosmic radiation, and extreme temperature swings for roughly ten days, according to the summary of the mission preserved on Wikipedia’s tardigrade entry. It marked the first time any animal had been deliberately exposed to the unfiltered environment of open space and survived.

Surviving Vacuum and Radiation Together

Open space presents a combination of hazards that few organisms ever have to face at once: a near-total vacuum that would cause uncontrolled water loss in most tissue, temperatures that swing from scorching in direct sunlight to deeply frozen in shadow, and a flood of solar ultraviolet and cosmic radiation with no atmosphere to filter it. Each hazard alone is capable of shredding DNA or destroying the proteins that keep a cell functioning. Tardigrades that had entered the tun state before launch reduced their exposed surface chemistry to a near-glassy, inactive condition, which appears to have limited the damage that vacuum and temperature extremes could inflict during the flight.

Coming Back to Life After Rehydration

When the FOTON-M3 capsule returned to Earth, researchers rehydrated the recovered specimens and found that a meaningful share of the animals exposed only to vacuum revived within half an hour, resumed feeding, and in some cases went on to reproduce normally. Survival rates dropped sharply among tardigrades that had also been exposed to the full, unfiltered dose of solar ultraviolet radiation, though a small number still survived that combination as well. The result showed that vacuum exposure alone, once thought likely to be lethal for any animal, was not enough to permanently end a tardigrade’s life cycle.

A Presence in Nearly Every Habitat

Tardigrades are not rare animals confined to a single ecosystem; more than 1,300 species have been described, and they turn up in a striking range of environments, from the deep ocean floor to hot springs, from mountainsides to Antarctic moss beds, and even in the gutters and roof mosses of ordinary city buildings. Their tolerance for desiccation is thought to be an adaptation to life in these small, temporary pools of water, which can dry out unpredictably and leave any animal living there stranded unless it can survive without water for extended stretches. That everyday survival strategy on Earth turned out to be sufficiently robust to also withstand the far more extreme conditions of orbit.

Extremes Tardigrades Already Endure on Earth

Long before any tardigrade left the atmosphere, laboratory tests on Earth had already shown how far the animal’s tolerance extends. Individuals in the tun state have been chilled to temperatures near absolute zero and heated to well over the boiling point of water without dying once rehydrated, and dried specimens have been shown to withstand pressures several times greater than those found at the deepest point of the ocean. Researchers have also exposed tardigrades to acute radiation doses many times higher than what would be lethal to a human being, with many individuals surviving and going on to reproduce normally afterward. Taken together, these experiments painted a picture of an animal built to tolerate extremes long before the 2007 spaceflight put that reputation to its most literal test.

Why the Result Still Matters

The tardigrade’s space survival is more than a curiosity; it has shaped ongoing research into the biochemistry of desiccation tolerance, radiation resistance, and the limits of what is often called extremophile biology. Molecular biologists have since identified tardigrade-specific proteins, including one nicknamed Dsup for damage suppressor, that appear to shield DNA from radiation and oxidative stress, and similar protective sugars and proteins are being studied for possible use in preserving vaccines, blood products, and other biological material without refrigeration. Later spaceflight experiments have built on the original TARDIS results, sending live tardigrades to the International Space Station to study how longer stretches of microgravity and radiation exposure affect multiple generations of the animal rather than a single ten-day flight. The tardigrade’s brief trip to orbit remains one of the clearest demonstrations that Earth life can, under the right conditions, tolerate an environment as hostile as space itself.

This article was produced with the assistance of AI and reviewed by Morning Overview editors.

More from Morning Overview