Healthy baby mice have been born using freeze-dried sperm stored in the near-weightless environment of space. The Japanese team behind the gravity-breaking experiment on the International Space Station (ISS) says it shows that transporting the seeds of life away from Earth is feasible. Sperm banks could even be made on the Moon as a back-up for Earth disasters, they told a leading science journal. It is unclear if this will ever help humans populate space, however. Sustaining life in space is challenging to say the least. On the ISS, radiation is more than 100 times higher than on Earth. The average daily dose of 0.5mSv from the cosmic rays is enough to damage the DNA code inside living cells, including sperm. Microgravity also does strange things to sperm. In 1988, German researchers sent a sample of bull semen into orbit on a rocket and discovered that sperm were able to swim much faster in low gravity, although it was not clear whether this gave a fertility advantage. Another space test showed fish eggs could be fertilized and develop normally during a 15-day orbital flight, suggesting a brief trip into space might not be too harmful for reproduction – at least for vertebrates. The freeze-dried mouse sperm samples were stored on the space station for nine months before being sent back down to Earth and thawed at room temperature, Proceedings of the National Academy of Sciences reports. Although sperm DNA was slightly damaged by the trip, it still did the job of fertilising mouse eggs and creating apparently healthy “space pups”. Fertilisation and birth rates were similar to healthy “ground control” mice. The space pups had only minor differences in their genetic code and grew to adulthood. A select few were allowed to mate and became mums and dads themselves.