Tiny critters survive space travel

In 2007, a European satellite carried tardigrades into orbit and exposed them to the vacuum of space. While many survived the vacuum, only a few survived the additional brunt of unfiltered solar radiation.

The animals were tardigrades - also called water bears or moss piglets - eight-legged invertebrates about half a millimetre long, soft and rounded, with a face that looks faintly like a vacuum cleaner nozzle. They live in every ocean, every desert, and the moss on most rooftops on Earth.

When conditions turn lethal, a tardigrade does something almost no other animal can. It expels nearly all the water from its body - dropping from 85% water to about 3% - curls into a barrel shape called a tun, and shuts down. Metabolism falls to roughly 0.01% of normal. By any practical definition, it is no longer alive. It is also no longer mortal.

In this state, tardigrades have survived temperatures of 150°C and -272°C, a degree above absolute zero. They have survived pressures six times greater than the bottom of the Mariana Trench. They have survived doses of radiation that would kill a human a thousand times over. In space, they survived the vacuum by entering a dormant state, though they remain highly vulnerable to solar UV; while they possess a unique protein called Dsup to protect their DNA from X-rays, it isn't enough to stop the sun's raw ultraviolet rays from damaging them.

Add water and a few hours later, the tun unfolds, the legs start moving, and the tardigrade walks off looking for algae to eat.

In 2019, an Israeli lunar lander called Beresheet crashed into the Moon carrying thousands of dehydrated tardigrades. They are almost certainly still up there, scattered across the impact site, technically alive in the way that a seed is alive, waiting for water that will never come.

Probably.