When Elon Musk unveiled SpaceX’s plans for sending humans to Mars in September 2016, he had a remarkably cavalier attitude toward the dangers of space radiation.
"There’s going to be some risk of radiation, but it’s not deadly," he told the audience in Guadalajara, Mexico back then. "There will be some slightly increased risk of cancer, but I think it’s relatively minor. The radiation thing is often brought up, but I think it’s not too big of a deal.”
That’s not true, as NASA has repeatedly pointed out. Study after study demonstrates there’s a legitimate increase in mortality and morbidity rates due to prolonged exposure to radiation furiously zipping through outer space.
New findings published Monday in the journal Proceedings of the National Academy of Sciences illustrate the destructive effects space radiation can have on gastrointestinal (GI) tissue, disrupting normal physiological functions. While the findings are hardly surprising—radiation of any sort, from outer space or elsewhere, is bad for your health—they underscore just how little we know about the specific consequences these cosmic hazards portend, and how inadequately prepared we are for sending people on long missions into deep space.
“[The] gastrointestinal tract is important for astronauts’ nutrition and health during space mission especially long duration missions,” said Kamal Datta, an associate professor at the Lombardi Comprehensive Cancer Center at Georgetown University and a co-author of the study. “This is a first study of its kind on intestinal cell migration, and further in-depth studies will be required to develop medicines or other technological protection measures for astronauts’ risk reduction.”
Space radiation can come in many different forms, but one form of big concern is called galactic cosmic radiation, or GCR, which originates from outside the solar system and is comprised of high-energy particles that permeate deep space. The more time you spend traveling through deep space—say, during a six-month trip en route to the red planet to start a new life—the more you become exposed to GCR, the greater the chances are that you’ll develop health problems down the road.
GCR isn’t really a major issue for current and past astronauts: Earth’s magnetic field is a critical barrier against cosmic rays inundating the planet or any objects in low Earth orbit (including the International Space Station), and the longest time in deep space ever spent by astronauts in deep space was Apollo 17, which lasted only 12 days.
But there’s a big question about exactly what kind of damage a long trip to Mars or elsewhere might do to a future astronaut’s body. In this investigation, Datta and his colleagues focused on the effects of heavy ion radiation in the GI tract. Heavy ion radiation is much greater in mass compared to other components of space radiation like x-rays and gamma rays, and our current spaceflight shielding is woefully limited in protecting us against these particles. Meanwhile, GI tissue is notable for how fast it self-renews, with the top layers of cells replacing themselves every three to five days by facilitating a continuous migration of new cells upward. This rapid replacement works to keep gastrointestinal functions working smoothly and absorb nutrients, so astronauts can hardly afford to suffer GI problems during a months-long spaceflight.
The Georgetown team exposed a set of 10 identical mice to a “low” dose of iron ion radiation that would presumably be present in interplanetary space, using the NASA Space Radiation Laboratory’s (NSRL) instruments at Brookhaven National Laboratory on Long Island. The team examined those mice for up to a year after radiation exposure, and found that their GI cells failed to absorb nutrients as well as healthy mice or those exposed to gamma rays, due to disturbances in tissue layer replacement. The iron-irradiated mice also developed tumorous polyps in within the GI tract, and even suffered from DNA damage that created increased damage and disruption to the migration of cells needed to replace intestinal lining.
All of that sounds grim—but there are some important caveats about this study to take note of. Mice and humans do share a lot of the same biology, but they remain different organisms, and what happens to one species upon exposure to radiation will not necessarily happen to the other. “In the absence of human data,” said Datta, “this is the next best approach we can take.”
According to Jeff Chancellor, a nuclear physicist at Texas A&M University who was not involved with the study and has previously written about obstacles in studying space radiation, from what he can tell about the numbers, the “low dose” the researchers used is actually is about 150 times higher than what astronauts flying through interplanetary space would be exposed to. “They’ve given the equivalent of about a one- to two-year projected dose exposure, and they’ve given it in just a few minutes,” he told The Daily Beast. “You’re basically taking a shotgun at all these cells, and just bulldozing them. You’re not allowing for any regenerative effects, or adaptation that is naturally occurring by the body itself. You’re just assuming the worst.”
In addition, the GCR “encompasses almost every ion in the periodic table,” he said. “You have approximately, at any given time, 20 to 30 ions at hundreds of different energies imposing on a human subject in space,” which is a radically different environment than the single heavy ion beam exposed to the mice in this study.
“There’s space radiation, he said, “and then there’s the operationally relevant space radiation environment.” These are two different environments, and studying how human biologically is transformed by the former doesn’t help us prepare against the latter.
These problems aren’t necessarily a knock against the researchers; the researchers seem to have run the best sort of study they were able to run. “As far as I can tell, it’s a nice study,” said Chancellor. “It’s methodical, with a very sound scientific methodology.
“But,” he emphasized, “we’re just limited in how you can simulate the environment as it affects human biology.”
It would be incredibly useful to send humans into space aboard a rocket that costs hundreds of millions of dollars to launch, let the radiation just wash over them, and take notes. But we obviously can’t do that. Instead, we’re relegated to using animal models, exposing them to punctuated bouts of radiation instead of at a consistently slow, natural rate. The study’s findings illuminate something new about how space radiation could affect humans en route to Mars, but they also inadvertently highlight the reasons why we should take these new insights with a grain of salt.
For his part, Chancellor is trying to rectify these limitations and course-correct what he says is a recent increase in these types of studies making bolder and bolder claims. He currently has a new paper in peer-review that outlines a new model for more accurately reproducing on the ground the space radiation environment that would affect astronauts during different sorts of missions.
And recently, said Datta, “NSRL has also made available chronic low dose exposures over a month for better approximation of space radiation during deep space missions.”
The ultimate hope is that a better emulation of space radiation can help inform us in our development of solutions that protect us. After nearly sixty years of human spaceflight, we still don’t have a magic armor or a miracle pharmaceutical pill to counteract the effects of space radiation and keep our guts safe and sound. But we’re getting closer.