The four mice - two males and two females, numbered 6, 98, 154 and 186 - were chosen from dozens of candidates after more than two months of training and behavioral screening before launch. They were flown to a dedicated habitat on the Chinese space station aboard the Shenzhou-21 crewed spacecraft on October 31 and returned to Earth with the Shenzhou-20 crew on November 14.

After their return, one female mated on Earth and later delivered nine pups on December 10, of which six have survived, a rate researchers describe as within the normal range. Scientists report that the mother is nursing normally and that the surviving pups are active and healthy, indicating that short-term spaceflight did not impair the mouse's reproductive capacity.

"This mission showed that short-term space travel did not impair the reproductive capability of the mouse," said Wang Hongmei, a researcher at the CAS Institute of Zoology. "It also provides invaluable samples for the investigation of how the space environment influences early developmental stages in mammals."

The rodents were transported to the space station to be raised in orbit for about five to seven days, making them the first mammalian models used by China for in-orbit life science experiments. Researchers aim to use the data to better understand how microgravity, confinement and other space conditions affect mammalian physiology, behavior, stress responses and adaptation mechanisms.

The CSU said continuous, AI-powered monitoring tracked the mice's movement, feeding and sleep patterns throughout the flight, supplying real-time data to support decision-making in orbit. This capability, combined with post-flight biological analyses, will help scientists probe the impact of space on systems ranging from individual cells and tissues to whole organisms.

The mission also faced operational challenges after an adjustment to the return schedule tightened supplies of the mice's dedicated feed toward the end of their stay in orbit. While astronauts supplied water via a dedicated port in the habitat, scientists on the ground tested alternatives and selected soybean milk from astronaut food stocks as a temporary substitute until the mice could be brought home.

According to the CSU, completing a full experimental cycle with successful post-flight reproduction lays a foundation for more ambitious studies, including future attempts to have mice mate, conceive, give birth and raise offspring entirely in space. Researchers will continue following the development of the current litter and may examine whether the pups themselves can reproduce normally, shedding light on potential multigenerational effects of space exposure in mammals.

At a public science event in Beijing, CAS researchers announced that the four mice have been given the names Wangtian, Lanyue, Zhuiyun and Zhumeng, translating respectively to "gaze at the sky," "reach for the moon," "chase the clouds" and "follow the dream." The names were selected from online submissions collected during the mission, underscoring efforts to engage the public in China's expanding human spaceflight and space science programs.

The naming ceremony coincided with the unveiling of cartoon illustrations of the four space-traveled mice, co-created with Xinhua News Agency to help communicate the science to younger audiences. The event is part of a month-long "flying mice" exhibition at the National Zoological Museum of China, jointly organized by the CSU and the CAS Institute of Zoology, which offers visitors a closer look at how biological experiments are being integrated into China's space station missions.

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