In 2025, China sent four mice to Tiangong for about two weeks; one female later produced three litters of 9, 10, and 9 pups after returning to Earth

A mouse spent two weeks in space, then returned to Earth and produced more pups than the average lab mouse on the ground. That's one reason researchers are interested in how the experiment informs future space biology studies. According to a report, ‘China's "space mouse" Births Third Healthy Litter,’ published by the Chinese Academy of Sciences in 2026, four mice were launched aboard the Shenzhou-21 spacecraft on October 31, 2025, as part of China's first experiment with small mammals in space. The animals lived in a specially adapted habitat for two weeks in zero gravity before returning to Earth on November 14. The experiment drew widespread attention.

Back on Earth, the female mouse became pregnant within weeks.

Shortly after returning, one of the female mice became pregnant and gave birth to her first litter of nine pups on December 10, according to China Media Group and the Chinese Academy of Sciences' Institute of Zoology. She also had two more litters of ten and nine pups, the same sources reported. According to the Chinese Academy of Sciences, each litter was larger than the five-to-seven-pup average commonly cited for laboratory mice, though litter sizes in outbred strains can range more broadly. Researchers at the Institute of Zoology, Chinese Academy of Sciences, noted the result as part of the mission's findings.


Three litters, three distinct personalities

The first litter of pups, born soon after the mother returned from the mission, was less adventurous and stayed close to the walls of its enclosure. The second generation had more exploratory personalities. The third litter, however, was described by the scientists as the most confident and well-adjusted. Researchers will now observe how the animals develop and whether they can produce healthy offspring of their own. Because all three litters were conceived and born on Earth after the mother's return, the personality differences likely reflect environmental and birth-order factors rather than an inherited effect of spaceflight.

The closest thing science has to a human experiment

Mice are not chosen for orbital travel by accident. According to NASA's Rodent Research Program, these small mammals are useful for research because they share many biological features with us. Mice are also useful for short-term research because they mature quickly. The Chinese Academy of Sciences says the mouse genome is approximately 85% similar to the human genome. Because mice develop quickly, a short mission can produce useful findings. For China, the similarities are enough to justify the experiment, though the findings still need careful interpretation before being applied to humans. This is why both the rapidity of the mouse reproductive cycle and their overall speed of development are important factors. Sending a mouse to space and then observing viable offspring on Earth provides a useful test that would take much longer in humans.

Space parenthood already has a track record

China's experiment is not happening in isolation. A study, "Male mice, caged in the International Space Station for 35 days, sire healthy offspring," published in the journal Scientific Reports, found that male mice sent to the International Space Station for 35 days were able to sire healthy offspring after returning to Earth. Earlier research, conducted by a Japanese team, showed that reproduction was still possible after weeks in microgravity and may have informed China's latest experiment. Together, the two studies provide a broader picture than either one alone.

China's next trip to orbit will last much longer

Whether humans could safely conceive and give birth during a mission to the Moon or Mars remains an open research question. Using mice as a starting point for research into human reproduction does not make them a substitute for the complexity of human biology. But the results give researchers reason to continue, and Chinese scientists have said they will run longer-duration experiments to mimic six-month missions and answer questions a two-week mission cannot yet address. For researchers interested in a permanent human presence on Mars, this is a grounded step toward understanding whether mammalian reproduction could safely occur beyond Earth. And so far, the answer remains in the results of these mouse litters.