Mice run through the international space station
NASA
Living their best life.
MOUSTRONAUTS

Watch how much NASA’s space-station mice love microgravity

By Nicolas Rivero

NASA has sent mice on a dozen missions to the International Space Station since 2014, in a special habitat designed for microgravity. In their own way, the rodent astronauts are contributing to humanity’s quest to explore Mars.

Before NASA sends humans on that long journey, it wants to understand the effects of an extended stay in microgravity. Astronaut Scott Kelly famously spent a year in space to see what it would do to his body. It wasn’t great: His bones thinned, his muscles atrophied, his genes changed, and parts of his eyeballs got squished or swollen in ways scientists still can’t fully explain.

NASA has published its first report on a group of mice that spent 37 days in space—which the agency notes is “a long-duration mission on the scale of the rodent lifespan.”

Scientists studied video of the animals’ behavior to see how they adapted to weightlessness. At first, the rodents seemed hesitant and confused. Then they quickly mastered skills like using momentum to glide to their destinations and anchoring themselves to walls with their tails while they ate or groomed themselves.

The mice even developed a new behavior the scientists dubbed “race-tracking,” sprinting zero-gravity laps around their habitat as if it were a hamster wheel. Scientists aren’t sure why the mice did it. Their leading theory: It was fun. NASA says it probably wasn’t a stress response because the mice otherwise behaved normally.

“Behavior is a remarkable representation of the biology of the whole organism,” April Ronca, a NASA researcher and lead author of the mouse study, explained in a statement. “It informs us about overall health and brain function.”

At the end of their mission, the mice returned to Earth in good shape. They weighed as much as an ground-based comparison group and their coats were in “excellent condition,” NASA reported.

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