Freeze-dried sperm: The future of space colonies is being tested on the ISS

Billionaires like Jeff Bezos and Elon Musk are fast preparing their escape off-planet in the coming decade. But millions or billions of smaller passengers may not survive the trip. That’s because new research hints at a problem for male space travelers: their sperm may no longer be potent by the time they get there.

But there’s a solution: freeze-dry it.

In a first-of-its-kind experiment, a team of Japanese researchers freeze-dried samples of mice sperm and sent them aboard the ISS to see how well this crucial element of human life (and, well, a lot of life on Earth) will fair against the harsh radiation of space.

Even after six long years aboard the ISS, the team found that the mice’s space sperm sired equally healthy pups as its terrestrial control. An additional X-ray experiment predicts that this positive outcome could persist with up to 200 years of space radiation exposure.

Sayaka Wakayama, assistant professor of reproductive biology at the University Yamanashi and first author on the research, tells Inverse that these findings will help prepare humans for a new space age.

Wakayama and colleagues’ findings were published Friday in the journal Science Advances.

What’s new — Shuttling through space to lunar or Martian colonies may be standard practice for humans of the future, but today we still don’t know how these trips will affect the human body.

Data collected from astronauts on the ISS have shown that humans can experience bone loss and vision problems from even short stints in space, but no experiments have yet been done on how human reproduction — a crucial aspect of an eventual off-planet colony — would fair.

The effects of microgravity on reproduction in non-mammals like fish or birds have been explored previously, the authors write, but true exposure of mammalian reproductive cells to space radiation has not.

In their study, the research team sent freeze-dried samples of mice spermatozoa aboard the ISS without the need for special refrigeration to see whether their DNA would be irreparably damaged.

Why it matters — Figuring out whether or not radiation damages sperm, and eventually other reproductive cells — like eggs and embryos — will be essential for not only human survival but for the survival of all other species on Earth as well.

“I hope that preserving Earth's genetic resources such as sperm and embryos off-planet will lead to the preservation of Earth's resources in the future,” says Wakayama.

Here’s the background — Space — including low Earth orbit where the ISS lives — is chock full of radiation coming from intergalactic sources like cosmic rays (which originate outside the Solar System) and solar ejection events like flares.

While the ISS does have protective shielding, it’s not impregnable, and the researchers write that prolonged exposure to these kinds of particles could rewrite the DNA of animals’ reproductive cells. It could even transform species, in some extreme cases.

“If radiation were continuously irradiated into the body of a species and several mutations accumulated in germ cells over a long period of time, then the species would become a different species,” the authors write.

Trials of these radiative effects can be done at home on Earth, but these studies can’t quite mimic the effect of how these particles move through the vacuum of space. This new study finally offers insight into this question.

What they did — To start, the team extracted and freeze-dried sperm samples from 12 mice and sealed them in lightweight capsules to be sent aboard the ISS. Because these samples were freeze-dried and not fresh, they didn’t require any additional refrigeration (which would’ve added weight and cost to the experiment.)

The team also kept analog samples of freeze-dried mice sperm on Earth for comparison at the end of the experiment.

The space samples were sent back down to Earth in different intervals, including at:

• 9 months
• 2 years
• 5 years and 10 months

After retrieving the samples, the team used dosimeters (e.g. radiation detectors) to measure how much radiation the space sperm had endured.

“The total exposure of [the] sperm stored on the ISS for six years ... is about 170 times higher than the dose in the ground storage area (control area) stored at JAXA's Tsukuba Space Center,” says Wakayama.

Yet despite their extra doses of radiation, Wakayama says that both the space sperm and control sperm resulted in genetically normal pups after implantation in female mice on Earth.

“A total of 168 pups were born from sperm stored in space for 6 years, all of which had normal appearance and no abnormalities were found in comprehensive gene expression analysis,” says Wakayama.

“Some of the mice were mated after sexual maturity, and it was confirmed that healthy pups and grandchildren were born.”

What we don’t know yet — Despite the success of this experiment, there are still a lot of unknowns when it comes to reproductivity and space. For example, Wakayama says we don’t know yet whether freeze-drying human sperm would have the same effect — and getting approval to test this out may be an ethical minefield.

Scientists also aren’t sure yet how similar techniques would affect eggs or embryos, although Wakayama says there is a joint NASA and JAXA project preparing to test this called the Space Embryo project.

Wakayama says there are also other ethical issues to overcome, such as in a Noah’s Arc (or Interstellar, depending on your preference) scenario where freeze-dried sperm and eggs and human and livestock alike may be transported to new space colonies.

“Ethical issues must always be considered by us researchers,” says Wakayama. “In order for future generations of earthlings to go into space, we need to conduct a series of basic experiments to see the effects of many space environments.”

“Now that the establishment of a lunar base is becoming a reality, I believe we need to study how it will affect our descendants in the future.”

Abstract: Space radiation may cause DNA damage to cells and concern for the inheritance of mutations in offspring after deep space exploration. However, there is no way to study the long-term effects of space radiation using biological materials. Here, we developed a method to evaluate the biological effect of space radiation and examined the reproductive potential of mouse freeze-dried spermatozoa stored on the International Space Station (ISS) for the longest period in biological research. The space radiation did not affect sperm DNA or fertility after preservation on ISS, and many genetically normal offspring were obtained without reducing the success rate compared to the ground-preserved control. The results of ground x-ray experiments showed that sperm can be stored for more than 200 years in space. These results suggest that the effect of deep space radiation on mammalian reproduction can be evaluated using spermatozoa, even without being monitored by astronauts in Gateway.