Some of the hardiest organisms on the planet are so small you can’t see them without a microscope.

Tardigrades, or water bears, are microscopic creatures that can survive when most other earthly animals can’t. Space? Sure. Under extreme pressure (paywall)? Easy. After being frozen for years, like Han Solo’s carbonite cryptobiosis at the end of The Empire Strikes Back? No problem—and they’ll have viable offspring when thawed, too. And remarkably, they can somehow withstand high levels of radiation (paywall), which is “one of the things that’s guaranteed to kill you,” as Mark Blaxter, a geneticist at the University of Edinburgh in Scotland, told the BBC.

How water bears live in these extreme conditions is a mystery, but Japanese researchers just published eight years of work isolating a particular tardigrade-unique protein that stops their DNA from mutating when bombarded with radiation. The team was even able to use the protein to protect human DNA from radiation when the gene was inserted into human cells.

The researchers sequenced the entire genetic code of one species of tardigrade called Ramazzottius varieornatus. This species survives radiation (paywall), like the kind emitted by X-rays and cosmic rays in space (paywall), pretty consistently. They found a protein, which they called Dsup for “damage suppressor,” that prevents damage to R. varieonatus DNA when exposed to these kinds of radiation.

“What’s astonishing is that previously, molecules that repair damaged DNA were thought to be important for tolerating radiation,” Takuma Hashimoto, a biologist at the University of Tokyo and co-author of the paper, said in a press release. “On the contrary, Dsup works to minimize the harm inflicted on the DNA.”

The authors isolated the genes that code for this protein, and inserted it into a line of human kidney cells, all of which had the same genetic material. They exposed these modified kidney cells to four Grays worth of X-rays—an amount that would, if applied to a person over the entirety of her body, would cause radiation sickness and kill her within 30 days if she didn’t receive treatment. When treated with Dsup, these human kidney cells experienced 40% less damage than they would ordinarily, and could still reproduce. (Actual tardigrade cells were able to withstand much more radiation: 4,000 Grays of helium ion radiation, which is much more damaging than X-rays. )

Of course, this work looked only at human kidney cells—we’re nowhere near being able to translate tardigrade abilities to another living organism yet. But finding the first step to radioactive invincibility is a start to figuring out how humans may be able to survive in harsh environments, like space, in the future.