April Ronca/NPG Press

Microgravity changes human behavior. Astronaut Chris Hadfield said he learned to speak differently because he became accustomed to speaking through weightless lips. Aboard the International Space Station, people have invented games that are impossible to play on Earth: NASA’s Scott Kelly, for instance, once played a solo round of table tennis by slapping a floating ball of water between two paddles.

Humans share this trait with other space-faring mammals. Mice act differently in space, according to a report published this month in the journal Scientific Reports.

Twenty female mice lived aboard the ISS, in a newly installed NASA Rodent Habitat, for up to a month. Scientists at NASA Ames Research Center and other institutions filmed the mice. Rodents have been to space before, but the video provides the “first detailed behavioral analysis” of mice in a space habitat, the study authors wrote.

At first the mice groomed each other and huddled together, which wasn’t out of the ordinary. They somersaulted, as mice sometimes do on Earth. They ate, as normal.

The Rodent Research Hardware System lets scientists watch how the mice of the International Space Station behave. (NASA)

But something changed. After more than a week in space, young mice began to sprint and glide, as though they were zooming inside invisible hamster wheels. The scientists called this circling behavior, which they hadn’t seen before, “race-tracking.” Within a few days, other mice joined the fray. As a group, they ran laps around the habitats, reaching speeds of about a mile an hour. It’s strange to watch(which you can do in the video above).

The scientists aren’t sure why the mice did this. Perhaps the rodents were trying to balance their inner ears. It’s possible they were stressed. But exercise can be rewarding, the authors pointed out. Maybe these mice had invented, like Kelly and his water-ball table tennis, a new way to play.