How Do Water Bears Survive in Space?

Water bears, formally known as tardigrades, are minuscule invertebrates known for their remarkable resilience. These eight-legged creatures, less than a millimeter in length, can endure conditions that prove lethal to most other forms of life. Their astonishing capacity to survive the extreme environment of outer space has captivated scientists and sparked widespread curiosity.

The Journey Beyond Earth

Tardigrades’ journey into space began with the European Space Agency’s FOTON-M3 mission in September 2007. Dehydrated tardigrades were placed aboard the BIOPAN astrobiology payload, orbiting Earth for 10 to 12 days. They were subjected to the harsh conditions of low Earth orbit, including the vacuum of space, solar ultraviolet (UV) radiation, and cosmic rays.

Different groups of tardigrades, such as Milnesium tardigradum and Richtersius coronifer, were exposed to varying environmental stresses. Some were shielded from UV radiation, while others faced full exposure to the sun’s unfiltered rays. The experiments, including “Tardigrades in Space” (TARDIS) and “Tardigrade Resistance to Space Effects” (TARSE), evaluated their survival rates under these isolated and combined stressors. While exposure to the vacuum alone did not significantly affect survival, the addition of full solar UV radiation drastically reduced the number of survivors, indicating UV light’s damaging nature in space.

Mechanisms for Surviving Space

The tardigrades’ ability to endure extreme desiccation, a common feature of the space vacuum, relies on a reversible metabolic suspension known as cryptobiosis. They undergo anhydrobiosis, a state induced by the absence of water, curling into a compact, barrel-shaped form called a “tun”. In this tun state, metabolic activity can drop to less than 0.01% of normal levels, effectively halting life processes until conditions improve. Instead of water, their cells are filled with protective molecules like the sugar trehalose, which helps stabilize cellular structures and membranes, although not all tardigrade species rely heavily on this specific sugar.

Beyond sugars, tardigrades produce unique intrinsically disordered proteins, such as CAHS (cytoplasmic abundant heat soluble) and LEA (late embryogenesis abundant) proteins, which form a glass-like matrix within their cells. This amorphous structure protects cellular components from damage during dehydration. Their resilience to radiation, including cosmic rays, is attributed to an efficient DNA protection and repair system. A specific protein, Dsup (damage suppressor) protein, plays a significant role by binding to nucleosomes and safeguarding chromosomal DNA from harmful hydroxyl radicals. Dsup also contributes to radiation resistance by upregulating DNA repair genes, allowing tardigrades to fix damage even in their active, hydrated state.

Scientific Significance of Tardigrade Survival

Tardigrade survival in outer space holds significance for the field of astrobiology. Their endurance supports the concept of panspermia, which hypothesizes that life could potentially travel between celestial bodies, perhaps embedded within meteorites or comets. While direct impact survival remains a challenge, the capacity for organisms to withstand space’s vacuum and radiation suggests a plausible mechanism for the dispersal of life across the cosmos.

Understanding tardigrade resilience offers practical applications for human technology. Research into tardigrade proteins, such as CAHS and Dsup, could lead to advancements in preserving biological materials like vaccines, pharmaceuticals, or even organs without the need for refrigeration. Insights into their radiation protection and DNA repair capabilities could inform improved radiation shielding for astronauts on long-duration space missions, or contribute to therapies for radiation-induced damage on Earth.

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