Explained: What is Tardigrade, the water bear?

Did the thousands of dehydrated tardigrades on Beresheet survive the crash? And if they did, are they now living on the Moon?

On April 11, the Israeli spacecraft Beresheet attempted to land on the Moon, but crashed on the surface. It was carrying a number of items including thousands of specimens of a living organism called tardigrade. The tardigrade, also known as water bear, is among the toughest and most resilient creatures on Earth. The question is: did the thousands of dehydrated tardigrades on Beresheet survive the crash? And if they did, are they now living on the Moon?

The tardigrade can only be seen under a microscope. Half a millimetre long, it is essentially a water-dweller but also inhabits land and, a 2008 study found, can survive in the cold vacuum of outer space. In 2017, another study found that if all other life were to be wiped out by a cataclysmic event a large asteroid impact, a supernova or a gamma-ray bursts the tardigrade would be the likeliest to survive. The tardigrade can endure extreme hot and cold temperature levels.

Although the tardigrades on the spacecraft were dehydrated, the organism is known to come back to life on rehydration. In fact, they themselves expel water from their bodies and set off a mechanism to protect their cells, and can still revive if placed in water later. However, there is no evidence of liquid water on the Moon, although there is ice. Without liquid water, it is possible that the tardigrades will remain in their current state, unless future astronauts find them and revive them in water.

The tardigrade derives its name from the fact that it looks like an eight-legged bear, with a mouth that can project out like a tongue. Its body has four segments supported by four pairs of clawed legs. A tardigrade typically eats fluids, using its claws and mouth to tear open plant and animal cells, so that it can suck nutrients out of them. It is also known to feast on bacteria and, in some cases, to kill and eat other tardigrades. Although they are famed for their resilience, they are destructible too. Should a human being swallow a tardigrade with her food, her stomach acid will cause the flesh of the tardigrade to disintegrate.

On the Moon, should they find liquid water and revive, the tardigrades might not last very long in the absence of food and air, according to Live Science magazine, which quoted Kazuharu Arakawa, a tardigrade researcher at Keio University in Tokyo.

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