Science Puzzle
How Can an Animal Survive the Vacuum of Space?
In 2007, scientists sent thousands of tiny animals called tardigrades, or water bears, into orbit on a satellite. For 10 days they sat in open containers, exposed to the airless vacuum of space. Back on Earth, given a drop of water, many of them woke up and walked off, and some went on to lay eggs that hatched.
A person in a vacuum would pass out within about 15 seconds. How can a tardigrade survive it?
The Answer
It dries itself out almost completely and switches off. With hardly any water left in its body, there's nothing for the vacuum to boil away or the cold to freeze, and it can wait until water brings it back to life.
When its home, often a patch of moss, dries up, a tardigrade pulls in its legs and head and shrivels into a tiny, dry barrel called a tun. It loses nearly all its water and its body chemistry almost stops, a state called cryptobiosis. Special sugars and proteins fill the spaces where the water was, setting like glass and holding the insides of its cells in shape so they aren't torn apart.
A vacuum is deadly to most living things because the water in their bodies boils and their tissues swell and burst. A dried tun has almost no water to lose. Add water, and within minutes to hours the tardigrade swells up, unfolds and walks away.
Tuns have survived being frozen to within a degree of absolute zero, and tardigrades frozen for 30 years in Antarctic moss have been revived. They're not invincible, though. In the 2007 experiment, the ones left unshielded from the Sun's ultraviolet light mostly died.
The principle: Cryptobiosis. By drying out almost completely and pausing its body chemistry, a tardigrade removes the water that a vacuum would boil and cold would freeze; it revives when water returns.