Bake them, freeze them, fire them from a gun, or blast them into space: tardigrades can survive almost anything. Some experts even think this eight-legged micro-animal could outlive every other species on Earth – including humans – and survive right up until the Sun dies.

If you went into outer space without protection, you'd die. Yet a tiny animal no larger than 1mm long – about the size of a pinhead – has survived this and more. Under the microscope, tardigrades, also known as water bears or moss piglets, are fearsome looking creatures. Their podgy misshapen faces, ferocious claws and dagger-like teeth make them look more like a monster from Doctor Who than an animal.

Now scientists are trying to harness their superpowers for our own use – from protecting cancer patients from harmful radiation therapy, to preserving food and medicines during long-duration, deep-space exploration.

So far, scientists have identified around 1,500 species of tardigrade. Closely related to arthropods – which include insects and crustaceans – scientists have not yet determined where exactly where in the animal kingdom these creatures deserve to be classified.

Tardigrades love to hide out in damp environments where there is plenty of moss, lichen and leaves. You may even find them in your back garden. But they are also famous for being able to survive in extremely inhospitable places. They have been discovered up mountains in the Himalayas, at the bottom of the ocean, in Antarctica, and even in highly acidic Japanese hot springs – although this finding hasn't been replicated.

It's not just the harsh environs of Earth that tardigrades can live in. In 2007, tardigrades became the first-known animals to survive being blasted into space. When the satellite they were travelling on returned to Earth, scientists found that many – but not all – survived. Some of the females had even laid eggs in space, and the newly hatched young were healthy.

Tardigrades were also aboard a 2019 Israeli mission called Beresheet, which attempted to land on the Moon, although the probe crashed with its microscopic passengers in tow and it is unclear if they survived.

Scientists keen to test the survival limits of the tiny creatures have put them through a battery of tests. As a result, we know that tardigrades can withstand a huge amount of radiation – up to 1,000 times the lethal dose for humans. They can also cope with being heated to 150C (302F), and being frozen to just 0.01C (0.018F) above absolute zero. In 2021, scientists even fired bullets with tardigrades inside to see if they could survive the impact. The study showed that tardigrades could survive being fired at speeds of up to 900m per second (3,000km per hour), which is faster than a bullet fired from a typical handgun.

So how do these seemingly insignificant creatures survive in such extreme conditions, and why have they evolved these superpowers? It turns out that tardigrades have a host of tricks up their sleeves.

One environmental extreme that tardigrades have evolved to cope with is desiccation (essentially being dryed out). For most animals, life without water is completely impossible. As cells dry out, the membranes that hold them together shrink and lose volume.

"All the stuff that's normally inside the cell gets smooshed together," says Thomas Boothby, an assistant professor studying the biochemistry and mechanisms of extremotolerant organisms at the University of North Carolina at Chapel Hill, US. "Then the proteins start to clump and stick together. They become non-functional; they don't work anymore."

Somehow tardigrades can avoid all this, but how? One of the clues to this question came in 1922, after a German scientist found that when a tardigrade dries out it retracts its head and eight legs, before entering a deep state of suspended animation that closely resembles death.

"They literally pack their organs away, concentrating them within an extremely small, confined space," says Nadja Møbjerg, associate professor of cellular biology and physiology at the University of Copenhagen.

In this "tun" state, the tardigrade's metabolism slows to 0.01% of its normal rate. It can stay in this shrivelled state for decades, only reanimating when it comes........

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