The first animal in open space
The unassuming science campus of the University of Tübingen is the site for astrobiology. This is where research connected to the TARDIS (Tardigrades in Space) experiment confirmed that an animal could survive the lethal environment of outer space. In September 2007, the European Space Agency's FOTON-M3 mission launched from Kazakhstan, carrying a small container with about 3,000 dehydrated tardigrades. For 10 to 12 days, the orbital module exposed these microscopic invertebrates to the hard vacuum and cosmic radiation of low Earth orbit.
Scientists used two species of tardigrade for the experiment: Richtersius coronifer and Milnesium tardigradum. The creatures were divided into groups. Some were exposed only to the vacuum of space, while others faced both the vacuum and the full spectrum of solar UV radiation. Upon their return to Earth, the tardigrades were rehydrated. Over 68% of the tardigrades protected from solar radiation were successfully reanimated. They survived but went on to lay eggs that produced healthy offspring. A smaller number of the tardigrades exposed to the full blast of solar radiation also survived, making them the first animals known to endure the combined vacuum and radiation of space.
A state of suspended death
The tardigrade's incredible resilience comes from a process called cryptobiosis, a state of reduced metabolism. When faced with extreme environmental stress like dehydration, a tardigrade retracts its eight legs, curls into a ball, and expels up to 97% of its body's water. This desiccated, barrel-shaped form is called a tun. In this state, its metabolism slows to less than 0.01% of its normal rate.
This death-like state is made possible by unique biological molecules. For a long time, the sugar trehalose was believed to be the primary protectant, forming a glass-like matrix inside the cells to preserve their structure. More recent research has identified a suite of unique tardigrade-specific proteins called Cytoplasmic Abundant Heat Soluble (CAHS) proteins. When a tardigrade desiccates, these proteins form a gel-like bioglass inside the cytoplasm. This gel locks cellular components in place, preventing the damage and degradation that would otherwise occur from a complete loss of water. This allows the tardigrade to remain in a tun state for decades, waiting for the return of water to reanimate in a matter of hours.