Meet the Tardigrade: The Toughest Critter in the Known Universe

If you've never heard of a tardigrade, prepare to feel slightly inadequate. These microscopic eight-legged animals — nicknamed "water bears" or "moss piglets" — measure less than a millimeter, look like tiny armored potatoes with legs, and are arguably the toughest organisms on Earth.

The secret to their survival is a process called cryptobiosis. When conditions get terrible, tardigrades can essentially pause all their biological functions — replacing most of the water in their bodies with a protective sugar — and curl into a dried ball called a "tun." In this state they can survive temperatures from -272°C (near absolute zero) to 150°C, intense radiation, pressures six times greater than the ocean's deepest trench, and the complete vacuum of outer space.

In 2007, the European Space Agency tested that last claim by attaching live tardigrades to the outside of a spacecraft and sending them into orbit with zero protection. They spent ten days exposed to cosmic radiation and the void of space. When the craft returned, the tardigrades were rehydrated — and most of them survived. Some even managed to lay eggs in space that hatched successfully back on Earth.

Scientists estimate tardigrades will likely outlive the entire human species. Only something capable of boiling away Earth's oceans — a nearby gamma-ray burst, say, or a direct asteroid hit — would be enough to finally finish them off. Sleep tight.