Over the past few years, our home planet has faced significant challenges, from the global spread of a pandemic to unprecedented heatwaves and natural disasters. These events underscore the rationale behind the futuristic concept of establishing extraterrestrial habitats, with advocates arguing that lunar or Martian outposts could serve as a safeguard against potential extinction events or human-induced catastrophes.

However, our understanding of the human capacity to survive and reproduce in space is limited, particularly concerning the ability to procreate. Recent research involving freeze-dried mouse sperm aboard the International Space Station (ISS) aims to shed light on the potential for mammalian reproduction off-planet.

Professor Teruhiko Wakayama from the University of Yamanashi’s Advanced Biotechnology Centre is at the forefront of this research. He is examining mouse sperm samples that have been stored in a radiation-protected container on the ISS. These specimens are expected to return to Earth in the coming year, where Wakayama will assess the effects of the space environment on their viability and their potential to produce healthy offspring. In his Japanese laboratory, Wakayama is also developing a device designed to facilitate rodent in vitro fertilization (IVF) on the ISS in the near future. His ultimate goal is to establish a system for the secure and permanent preservation of Earth's genetic resources in space, ensuring the revival of life in the event of Earth's catastrophic destruction.

While Wakayama's work may seem like a plot from a science fiction film, he has a history of pushing the boundaries in reproductive science. In 1997, he co-developed a novel method that led to the cloning of the world's first mouse from adult cells. He has also led a study on the development of mouse embryos in space, a feat previously achieved only with species such as amphibians and fish. His team pioneered a freeze-drying technique to send mouse sperm to the ISS, where it was preserved in a freezer for up to six years. Upon return to Earth, the samples were rehydrated, resulting in the birth of healthy baby mice. This study concluded that freeze-dried sperm could remain viable for up to 200 years in space, although Wakayama considers this duration insufficient for long-term space colonization.

With his latest space specimens, Wakayama is employing a new device to protect sperm stored at room temperature from radiation, exploring the possibility of indefinite storage in space. For decades, scientists have been sending Earth's creatures into space to study the impact of microgravity and cosmic radiation on biological processes, including reproduction. In 1989, for instance, 32 fertilized chicken eggs were launched into orbit to study their development without gravity, an experiment sponsored by KFC and dubbed "Chix in Space." Tadpoles born on the Space Shuttle Endeavour in 1992 marked the first vertebrates to spend their initial days in space, exhibiting erratic swimming and difficulty breathing. In 2007, a cockroach named Nadezhda, which means "Hope" in Russian, gave birth to 33 offspring conceived in orbit, most of which were normal aside from their unusually dark exoskeletons.

"We have observed that specific phases of the reproductive cycle can occur in space, at least in a few species, though not always entirely successfully," said Virginia Wotring, a professor at the International Space University in Strasbourg, France, a private non-profit institution dedicated to space education. Medaka fish, native to Japan's rice paddies, marshes, and ponds, and snails have completed the entire reproductive cycle in space, according to Wotring. "Progressing to mammals is the next logical step to determine which aspects of reproduction are feasible," she added.

Regarding mice, the freeze-dried mouse sperm Wakayama is currently storing on the ISS is scheduled to return to Earth in 2025 for further study. "Our objective is to preserve reproductive cells at room temperature indefinitely," he stated. While humans are far from becoming a multi-planetary species, progress is being made. The NASA-led Artemis program, set for late 2026, aims to return astronauts to the moon for the first time since 1972, with the intention of establishing a sustained presence. If SpaceX founder Elon Musk's predictions are accurate, the first crewed mission to Mars could be underway within the next four years.

Scientists are already aware that space travel can have detrimental effects on the human body. Cosmic radiation can induce DNA mutations that increase the risk of cancer and other diseases. Microgravity can lead to vision problems, a weakened immune system, and the loss of muscle and bone mass. According to Wotring, there are more pressing concerns than reproduction, stating, "There is other critical information we need now to care for the astronauts we are sending to space, which must take priority."

However, Wakayama believes his research will be essential as humans spend increasing amounts of time in space. Damaged DNA in sperm and eggs, for instance, could pass genetic abnormalities to the next generation, he says. Additionally, without the directional influence of gravity, a fertilized embryo might not develop properly. "The formation of the nervous system and the development of limbs... we do not know if these processes will occur correctly in microgravity, where there is no distinction between up and down," he said. He also suggests that his work could be replicated and expanded for other species, which could be beneficial for transporting animals like dogs for companionship and livestock like cattle for food to other planets.

Wakayama plans to focus on studying mice. His IVF project has been approved by Japan's space agency, but the device required for the IVF procedure is still in development. He hopes it will be ready for launch to the ISS within two years. "In science fiction movies, people live on other planets, and babies are born, but we do not yet know if that is possible," he said. His experiments aim to provide clarity on whether humans can reproduce and develop normally in the harsh conditions of space. "If we can confirm that, it will bring reassurance," says Wakayama. "And if it does not work, we need to understand how to address that challenge."