Lengthy stays on board the International Space Station don’t seem to hurt sperm fertility. In a new study, mice on Earth successfully gave birth to litters of pups after being fertilized with sperm that had been freeze-dried for nearly a year on the ISS. It’s potentially good news if, one day, animals and people will have to reproduce beyond Earth. But experts say there is still a lot more research that needs to be done to fully understand how the space environment affects reproduction.
The point of this study, published today in the journal PNAS, was to see if the sperm experienced extensive DNA damage while in orbit around Earth. On the ISS, people receive between 10 to 100 times more radiation than they do on our planet, and the parts of the body most sensitive to that exposure are the reproductive organs.
Sure enough, the sperm from space, which stayed on the station for 288 days between 2013 and 2014, had a bit more DNA damage when compared to sperm that had remained on Earth during that time. However, it didn’t affect the sperm’s ability to fertilize eggs back on our planet. The genome of the resulting offspring was also totally normal and only had minor differences than the pups born from the sperm on Earth, according to the study authors. “We got many healthy offspring from space sperm,” Teruhiko Wakayama, a biologist at the University of Yamanashi in Japan and lead author of the study, wrote in an email to The Verge. “Those pups could not have any genetic damage.”
Having kids in space or on other planets is an important topic for those with dreams of establishing a colony on Mars or elsewhere beyond Earth. And knowing how radiation affects sex organs is just the first step in figuring out if reproduction in space is even possible. The problem, though, is this study barely scratches the surface of the issues associated with sex in space. Radiation is a major concern, but another major variable is how a fetus would grow in an environment without gravity. And we are still uncertain how that would play out.
“No one got pregnant in space and had the baby,” Dorit Donoviel, associate professor at the Center for Space Medicine at Baylor University, who was not involved with the study, tells The Verge. “An ideal experiment would be to really have mice mate and deliver a litter of pups in space, and I don’t even know if the mating is even feasible for mice in zero gravity.”
Plus, this experiment does not fully capture the radiation exposure that sperm might experience on a mission to Mars, for instance. There are two major sources of space radiation: highly energized particles streaming out from the Sun or deep-space cosmic rays — particles traveling near the speed of light that stem from distant stars either within or beyond our galaxy. On Earth, we’re protected by this radiation thanks to our atmosphere and magnetic field; the magnetic field around our planet, known as the magnetosphere, deflects or captures the incoming particles, and the ones that make it through are mostly absorbed by our atmosphere.
Since the ISS is outside the bulk of our atmosphere, it is exposed to higher doses of these particles. However, the station is still within our magnetosphere, which offers a lot of protection. But anyone traveling to deep-space destinations will be exposed to highly energized particles that can potentially cause a lot more severe DNA damage.
Even though astronauts on the ISS are protected from a lot of radiation, they are counseled about cryopreserving their sperm and eggs just in case, according to Joseph Tash, a professor at the University of Kansas Medical Center who studies how space may affect male and female reproductive health. However, many astronauts have returned home from lower Earth orbit and have had no problems with fertility, according to Donoviel. “I’m not surprised this sperm is fine,” she says. “We know that astronauts who come back from space have been just fine and have had children normally.” She argues that our body has mechanisms for selecting against survival of sperm and eggs that are very damaged.
To really understand the radiation risks, an experiment would need to be done beyond Earth’s protective magnetic shield. But Tash says the only way reproduction in space can be made possible is if “radiation-hardened” facilities are created, to protect growing embryos from exposure. “Given the nine-month gestation for humans, the pregnant mother would also need to be protected by such a facility,” he adds. “So it presents very real habitat, medical, social, and psychological questions that need to be addressed as well.”
But for now, Donoviel says we really need to study if a baby can even grow in a microgravity environment. Since it might be difficult to have mice mating in space, she envisions an experiment in which female mice are launched to the station as soon as they become pregnant and then give birth when they’re up there. That way, the pups develop most of the time in zero gravity. Similar experiments were done in the ‘90s, when pregnant rats were flown for a short time on board the Space Shuttle. The rats gave birth back on Earth, and their offspring had problems properly orienting themselves. Donoviel says there might be even more issues the longer a fetus develops in space. “Embryo development would not be normal, because I think gravitational forces may play a role in how the different organs form,” she says.
Getting pregnant on Mars, though, may be a different story since the planet has one-third the gravity of Earth. Still, it’s unclear how partial gravity may affect a developing embryo, and we won’t know until we test it out. But that’s far away into the future. For now people shouldn’t be thinking about having kids in space anytime soon, Donoviel says. “We’ve got our hands full just keeping adults healthy,” she says. “The last thing I want to worry about is a baby who is going to be a lot more vulnerable.”