Most creatures require a specific set of conditions to survive: a certain amount of oxygen, temperature, pressure, food, etc. However, some animals can live in conditions so extreme they kill almost everything else. These animals are called, fittingly, extremophiles. One extremophile is the tardigrade, more commonly called water bears or moss piglets.
In general, tardigrades hang around on moss, sucking up water. However, for some reason, they are able to withstand almost unimaginable conditions. Temperature-wise, they have survived temperatures of over 304° F (151° C) and down to -423° F (-253° C). Tardigrades can also survive at extreme pressures. Some species can survive at pressures 6,000 times that of atmospheric pressure, almost six times the water pressure at the bottom of the Mariana Trench. Tardigrades have also been shown to survive radiation doses of over 500 times what would kill a human. The tardigrades accomplish these incredible feats by entering a state of cryptobiosis. In doing so, they will curl up and dehydrate themselves. Tardigrades have been known to survive up to ten years in this state. We don’t know why tardigrades can live in conditions so extreme they aren’t found on Earth, but we are trying to understand them.
Now, as astronomy students, you would probably guess that the most hostile environment in the universe is outer space. With temperatures of a few degrees above absolute zero and an almost complete vacuum, it seems impossible that anything could survive. However (as you might have guessed), tardigrades are able to survive in outer space. In 2007, NASA let a bunch of tardigrades out into the vacuum of space where they were exposed to incredible amounts of solar radiation. Ten days later they let the tardigrades back in, and when they brought them to Earth, the tardigrades were fine, and some even laid eggs that became perfectly normal baby tardigrades. This experiment has been repeated multiple times, with the ESA also sending tardigrades into space in a mission they called Tardigrades in Space. You’re probably thinking the ESA does a terrible job naming things until you learn they shortened the mission name to TARDIS.
So, besides being awesome, why is this information useful? Well, it helps us understand how life might spread throughout the galaxy. If some tardigrades were ejected from Earth (by, say, a meteorite impact), and somehow they managed to land on another planet, they could bring life to that planet, assuming the planet could sustain life. This youtube video also does a good job explaining why tardigrades are so awesome.