Space travel is rough on the human body. And if scientists hope to send astronauts to Mars and beyond, they need to know a lot more about the effects of life with little or no gravity. So a group of scientists turned to a not-so-human species for clues: flatworms.

As UPI’s Brooks Hays reports, researchers sent a group of intrepid flatworms to the International Space station for five weeks to see how they’d fare and the weird results offer new insights into human health. They detail the amazing journey in a study published in the journal Regeneration.

“Much of what has been done in the past has been focused on astronaut health, and you can learn a lot from that, but we’re focused primarily on the cellular and molecular level processes that could impact regenerative processes on Earth,” says Kris Kimel, president and founder of Kentucky Space, which teamed up with Tufts University for the experiment.

Planarian flatworms are known for their amazing ability to regenerate themselves after being cut. So in 2015, researchers sent a set of the worms, some whole and some amputated, to the space station on the SpaceX Dragon spacecraft. The worms lived on the station for five weeks in test tubes filled with half water and half air. Meanwhile, back on Earth, the researchers took other sets of worms, sealed them in the same setup, and stored them in total darkness.

When the worms returned to Earth, they were subjected to a barrage of tests along with the control group. And there were some big differences. Initially upon their return, the space-faring worms were curled up and paralyzed, unlike their counterparts. But within two hours they uncurled. Researchers also tracked their movement in partially lit areas. The worms that had just returned from space spent significantly less time in the dark compared to the control group, and showed an altered metabolic state.

But things got even weirder as time passed. Not only did some of the whole space worms spontaneously divide in two, but one of the amputated ones grew back two heads—and when it was divided, its offspring did, too. In a press release, the researchers say it's the first time anyone on the team observed such behavior in more than 18 years of working with similar worms.

"Seeing a two-headed flatworm was pretty remarkable," Michael Levin, a Tufts University biologist who co-authored the paper, tells Smithsonian.com. And when the team cut off the new heads, they grew back. "These changes appear to be permanent, or at least long-lasting," says Levin.

There are, however, some limitations to the study. Researchers admit that it was difficult to keep the control group at the same temperature as the worms taken to space, and note that the amputations were performed on Earth when it would have been ideal to cut up the worms in space. And it’s nearly impossible to figure out which physical forces in space—as opposed to factors introduced during the flight and storage—made the difference in the worms. In the future, says Levin, they want astronauts to perform the amputations on the ISS so that the amputated worms spend less time in transit. And they hope to one day have the ability to observe their bread-loaf-sized experiment in real time to track the worms as they divide and reproduce in space.

Still, the study is an intriguing look into how space might affect humans. Sure, worms aren’t people, but the changes they underwent suggests that going to space can have some pretty dramatic effects. That tracks with other studies like a recent one that showed damage to mouse sperm in space.

The study also has implications for medicine back on Earth, says Levin. More than half of planarian genes are similar to human ones, but that's just the beginning. By studying how cells act when they escape the influence of gravity and Earth's magnetic field, he says, scientists can learn more about how those factors influence cells' decisions to divide, differentiate into different organs, and even stop growing.

"Experiments in space are so important," says Levin. "They allow us to look into the roles of physical forces, not just genetics."

That's right: One day worms might not just help people sneak past the potential dangers of life in space, but also be healthier at home.