In January 1991, a couple of crazy kids got married. That these particular “kids” were in their late 30s, were astronauts, and were keeping their marriage a secret from their bosses at NASA only added to the romance. Mark Lee and Jan Davis met during training for a space shuttle mission and kept their relationship quiet long enough to ensure that it would be difficult to replace them on the mission, as NASA normally would have done under its then-unwritten rule that banned married astronauts from flying together. And so, in September 1992, Lee and Davis became the first (and, after the unwritten rule became a written one, possibly last) married couple in space.

America had just one question for them. You know. Eh? Eh? Wink-wink.

NASA says no humans have had sex in space. There’s nothing other than speculation to suggest otherwise. (Well, speculation and a vague sense that we would want to try it, given half a chance.) But you aren’t a total junior-high pervert for wondering. Sex — or, rather, reproduction — has piqued the curiosity of scientists, too. When they went to space together, Lee and Davis even spent some time artificially inseminating frog eggs for the greater good. (So, somebody got lucky on that trip. Sort of.)





No one has gotten lucky in space

If the future of humanity is written in the stars, and if we’re really serious about permanent human settlement on Mars, then we need to know what happens when this basic biological function is taken beyond the confines of the planet on which it evolved. And this is about more than just sex. Experts say that whether and how reproduction works is just one of a number of medical and biological questions related to long-duration space travel to which we need better answers and more, more-diverse data. Right now, anybody who wants to take a human to Mars for a trip that would last a minimum of nearly two years is, in many ways, flying blind.

The research on reproduction in space has been slow and underfunded. It’s happened in fits and starts over the course of 50 years. All told, at least five species — from amoebas to rats — have gone through the, er, act of reproduction while in orbit. Other species have spent part of their gestation in space or donated their space-altered sperm and eggs to science.

The data that has come out of this research is not altogether reassuring. Space travel can affect reproduction in a couple of ways. First, most obviously, is the radiation. Space is full of subatomic particles moving very quickly. Those particles can slam into DNA like a bowling ball laying down a sweet split. The damage they leave behind can alter genetic instructions, setting up a path that leads to cancer, genetic mutations that can be passed down to children, and other problems. Life on Earth is protected from more than 99 percent of this radiation by our planet’s atmosphere and magnetic field. The magnetic field provides some protection in orbit as well. But the farther from Earth you go, the less you’re shielded. And “if you look at the list of organs sensitive to radiation damage, the gonads, the ovaries and testes, are always in the top two or three,” said Joseph Tash, a professor at the University of Kansas Medical Center who has studied animal reproduction in space. Any trip to Mars would result in radiation exposures exceeding the current allowed limits for astronauts.

The second source of danger is less well-understood. Microgravity — you know, the whole thing where astronauts float around the International Space Station like a Cirque du Soleil troupe with a penchant for polo shirts — seems to alter biology too. It’s well-known that astronauts lose muscle mass while in space. Your body gets weaker when it doesn’t have to bear its own weight every day. But the effects of microgravity are weirder and more complex than what can be addressed by a modified treadmill. Some of the female mice that traveled to the space station in 2010 and 2011 stopped ovulating, and others lost their corpus luteum, an important structure that forms in the ovary after the release of an egg. The corpus luteum is responsible for producing hormones that maintain a pregnancy until the placenta can grow enough to do that job itself. Without it, you might get pregnant, but the pregnancy would be unlikely to stick.

This connects to data from older experiments. Back in 1979, Russian scientists launched a satellite carrying male and female rats and gave them the opportunity to mingle beginning a couple of days into their 18-day trip. The experiment didn’t result in any babies. Two rats had apparently gotten pregnant, but both miscarried. There’s consistent evidence that microgravity affects hormone levels in both males and females, Tash said. It’s possible those rats had estrogen levels so low that most of them weren’t even interested in mating. These effects persist after the animals return to Earth, but things eventually reset after they spend enough time in normal gravity. Mars’s surface doesn’t have normal gravity, however. It’s about 38 percent of the gravity of Earth. And we don’t know if that’s enough to reverse the effects.

We also don’t know whether humans experience these same effects. We only have a very small sample of female astronauts to begin with — as of 2015, only 11 percent of people who have gone to space have been female. These women are also typically in their late 30s when they first go to space, and most of them choose to take hormonal birth control to stop menstruating while they’re there. It would be very difficult to statistically separate the impact of microgravity on their hormones and fertility from the impacts of their age and medications. As for men, there’s evidence that both pilots and astronauts who spend time in altered gravity father more female than male babies. But again, these trends give rise to more questions than answers.

Microgravity has been implicated in changing sperm production and behavior. It could alter fetal development, particularly the vestibular system, which helps you maintain your balance when you walk. Rats who go into labor shortly after returning from space have almost twice as many contractions as rats who never left Earth. Tash told me that researchers are only on the cusp of beginning to understand why microgravity can alter the body in the ways it apparently does. The basic takeaway, according to him and to Virginia Wotring, professor at Baylor University’s Center for Space Medicine, is that we don’t know much. But what we do know should give us pause.

Far from being seen as crucial, though, the research on reproduction in space has often been treated as if it’s somewhat embarrassing. In 2007, for instance, somebody from NASA told Slate that the agency had never conducted official experiments on animal reproduction in space, a claim that appears to be in direct opposition to the published scientific record. And Kelly Humphries, acting news chief of the NASA Ames Research Center, told me the agency decided not to comment on this story and would not allow me to speak to April Ronca, a senior scientist with NASA’s space biosciences research branch and the foremost expert on this topic. NASA is not focused on sex in space at this time, Humphries told me.

And that is where your prurient giggling connects to a much larger issue. When you ask why no humans have ever had sex in space, part of the answer is that truly living in the cosmos — as opposed to visiting for the sake of scientific field research — isn’t what NASA is about. Stressing that she was not speaking on behalf of NASA, Wotring said, “It’s never been one of NASA’s missions to colonize. Yet. The way the budgets are constrained, you can’t afford to do research on something you don’t need. There’s all kinds of things we should do before a long-duration kind of mission, but [we] haven’t, because we haven’t needed it,” she said.

Turns out, we know very little about the impacts of long-duration spaceflight in general. The open questions include whether some medications would lose efficacy in less time than it would take to get to Mars and back, and whether spaceflight-weakened astronauts would be able to regain their muscle mass in Martian gravity they way they do on Earth. “They have a massive team of people to assist with rehabilitation back to Earth’s gravity. And even then it can take days, weeks, or even months to recover,” said Dr. Kris Lehnhardt, professor of medicine at George Washington University and faculty associate with the school’s Space Policy Institute. Those rehabilitation teams won’t exist on Mars. So what happens then? “We can’t have everybody laying on the floor of the spacecraft because they pass out whenever they try to stand,” Lehnhardt said.

Part of the problem is that almost all the available data on astronaut health and recovery comes from astronauts who have experienced only very short stays in space. During the space shuttle era, most people were only ever off the planet for about two weeks at a time. Since then, missions have lengthened significantly. Six-month stays on the ISS are now more normal, and astronaut Scott Kelly and cosmonaut Mikhail Kornienko completed a yearlong mission in March.

What we think we know, based on mostly short-trip data, might or might not turn out to be accurate when applied to longer journeys. In testimony to Congress in June, Kelly said that the physical impacts of his 340-day trip were surprisingly different from those he experienced after a 159-day mission. His muscles stiffened more quickly. His legs swelled. He developed a rash all over his body from touching everyday objects. He even had flu-like symptoms.

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NASA has acknowledged the gaps in what we know about the impacts of long-duration spaceflight. In 2014, for instance, it commissioned a team studded with health experts and retired astronauts to write a National Academies report advising the agency on how best to ethically approach long-duration spaceflight situations where the very nature of the mission would mean that astronauts must violate current NASA workplace safety standards.

But other groups interested in traveling to Mars have displayed less concern about these challenges. In the Q&A session after his Sept. 27 presentation unveiling his plan to put humans on Mars, Elon Musk was asked about human safety in flight or on the planet. His response downplayed the risks of radiation as minor, and he didn’t mention the effects of microgravity at all. When I asked Tash about Musk’s perspective, which seemed to imply that the problems had been solved already, Tash just started laughing. “Well, Elon Musk is a good salesman,” he said. “Unfortunately, a lot of people think, ‘There’s a pill for that.’ And there may not be. Based on our data and the data of people doing the fundamental research, we can tell you that no, we don’t know the answers yet.”

It’s not that SpaceX discounts the health impacts of long-duration space flight, said Phil Larson, who at the time he was interviewed was SpaceX’s spokesperson. (He has since left the company.) Instead, he told me, Musk’s comments have to be understood in the context of what, specifically, the inventor and his company want to do and what they want to leave to others. SpaceX’s business is building the machines to get to Mars. “If you can solve the transport problem — meaning dramatically lowering the cost per pound to the surface of Mars — then solving the other challenges, like health, becomes much easier,” he told me. The cheaper and more realistic the transportation becomes, the more incentive other people will have to answer questions about things like making babies.

Finding those answers will take cash, starting with increased investment in astronaut health. The 2014 National Academies report advised NASA to put more resources into caring for, and monitoring, the health of retired astronauts. “Believe it or not, there’s no provision for lifetime health care for astronauts,” said Jeffrey Kahn, director of the Johns Hopkins Berman Institute of Bioethics and chair of the committee that wrote the report. Without that commitment, there’s not a strong incentive for retired astronauts to be continuously monitored and cared for as they age — which means potentially crucial data about the effects of space travel on the human body is likely going unnoticed. That’s the first small step we can take. Eventually, maybe we’ll know enough to allow somebody — or, really, two somebodies — to take the giant leap of space sex and reproduction.

CORRECTION (March 14, 10:10 a.m.): A previous version of this article misstated Phil Larson’s job title. He was a spokesperson at SpaceX when he was interviewed, but he left the company before the article was published.