At the rate of current research and space exploration, it is not entirely unimaginable that humans will reside in Martian settlements in this century. The question then becomes: can humanity reproduce on other planets – or in spaceflight?
One obvious problem is that having sex in free fall or in low gravity will be a complex task. Another, more complex issue is whether and how the entire process, from fertilization to birth, is affected by the space environment. Humans have already sent different species – mice, rats, frogs, fish and salamanders – to study reproduction in space, but the results have been mixed and inconclusive.
“All of our big tech gurus out there who want us to be a multiplanet civilization—this is a key question that no one has answered yet,” said Baylor University physician Kris Lehnhardt, a specialist in space medicine. “Everyone is focused on the hardware, and the hardware is great, but in the end it’s the squishy meat-sack that messes everything up. Ignoring the human system, if you will, in future plans and designs is only going to lead to failure.”
On Mars, the gravitational pull is a bit more than a third of the strength of the pull on Earth. On Earth, magnetic fields also shield the planet from radiation, which is a serious concern for the health of astronauts who are exposed while traveling in orbit. How partial gravity affects reproduction, and how radiation could harm a fetus, are the big unknowns at this point. Because it would be unethical to send a human embryo into space for experimentation, scientists have been experimenting on animals and tissues sent into space.
Forty years ago, Russia sent several rats into orbits on a satellite. Surprisingly, although mating had taken place, none of the female rats delivered. NASA scientist April Ronca took it a step further and sent pregnant rats into orbit. While those rats did give birth to pups, the latter had problems with abnormal vestibular systems – the way they perceive their orientation and the direction of movement to establish balance. Ronca also discovered that space flight decreases sperm count in male rats. The entire process, Ronca wrote, is affected by altered gravity.
With mice, who are a different species of rodent, the research is similarly inconclusive. Embryos sent up on the Columbia shuttle failed to develop. And in simulated microgravity experiments, in vitro fertilization was shown to occur normally, but the embryos either failed to implant or to develop at rates that would fall within the normal boundaries.
There have been some successes and some failures, resulting in bits and pieces of information that thus far do not give scientists a conclusive picture. A recent Japanese study demonstrated that freeze-dried mouse sperm could still produce embryos after nine months in space. Crickets, nematodes and fruit flies can reproduce in spaceflight. The Japanese medaka fish both mated and produced offspring on the Columbia shuttle. Similarly, salamander eggs produced embryos, albeit with some alterations, on the Russian space station Mir. Sea urchin experiments also showed that fertilization can occur. But quail eggs kept in an incubator on Mir were unable to develop normally.
“If you were to take reproduction and break it down into all of its various parts … there’s never really been a dedicated scientific program that looks at how each of those steps is affected by the space environment,” Lehnhardt says. “It’s one thing to know that it’s even possible, it’s another thing to know that it can be done safely and have a good outcome.”
“Across the board, almost every study has shown that in space, either things don’t work at all or they’re not as good—and so as we move forward, we need better and bigger studies, and human studies,” says James Nodler of the Houston Fertility Clinic.
NASA’s Langley Research Center has designed an experiment, MICEHAB (Multigenerational Independent Colony for Extraterrestrial Habitation, Autonomy and Behavior health) to study the long-term effect of partial gravity on reproduction. The idea is to place a mouse colony with telerobotic animal care into lunar orbit, and observe them with 600 built-in cameras.
“Before significant investment is made in capabilities leading to such pioneering efforts, the challenges of multigenerational mammalian reproduction in a partial gravity environment need be investigated,” Langley researchers write. “Humans may encounter reproductive challenges in gravity environments different than Earth’s, as gravitational forces may disrupt mammalian life cycle processes and actively shape genomes in ways that are inheritable.”
Scientists intend to keep track of birth rates and overall animal health by annual meetings with a humans in cis-lunar space, where astronauts would retrieve samples and perform necessary repairs. The goal for the duration of the experiment is 10 years.
“Partial gravity mammalian reproduction research should be conducted prior to the late 2020s in order to inform design decisions on future human Mars missions,” write the researchers. “Permanent surface settlements may be infeasible if partial gravity reproduction challenges are too great to overcome.”
The major problem is that human reproduction varies drastically from that of other primates. “If you look at early IVF studies, they skipped over a lot of mouse and primate studies – it’s just not the same,” Nodler says. “It can’t be overstated that at some point, we have to do human studies to see what’s really going on here.” There is currently no set date for MICEHAB.
For now, however, animal experiments will have to do, as experimenting on human embryos is full of moral and ethical issues. Scientists could, theoretically, send viable fertilized embryos to the ISS and look at the effects of the space environment, but that would mean that the embryos will be subjected to abnormal development.
Nodler disagrees: “Let them stay frozen on ISS for six months or a year, then bring them back to Earth, and use them to try to have a live birth. That would be really, really difficult to get approval for, but at one point you gotta do it,” he says. The adds that “we have thousands of discarded embryos that patients have said we can use for scientific research. The problem is getting someone to let me use them for scientific research.”
Lehnhardt also says that studying human reproduction in space without studying humans slows down the research, but acknowledges the dilemmas. “The moral and ethical challenges are not going away,” he says. “So, we’re going to have to face those head-on as we work on stuff like this in the future.”
Photo credit: NASA