- To travel to Mars, we need to conquer (or heavily mitigate) the cosmic radiation.
- Treated windows and protective visors protect today’s astronauts from sunburn.
- To date, one astronaut has received a sunburn on exposed skin beneath a ripped spacesuit. Close call!
On Earth’s surface, our layers of atmosphere, cloud cover, and even the magnetic field created by our spinning electromagnetic core all partially protect us from the sun’s radiation. Our exposure to UVA and UVB radiation (see sidebar) varies by land surface, water depth, latitude, and more. But what about the astronauts who live aboard the International Space Station (ISS) for months at a time? Or explorers headed for Mars? They don’t have these protections, and they’re additionally exposed to cosmic radiation we don’t experience on Earth’s surface. Should they all be covered in zinc oxide to prevent the mother of all sunburns?
Right now, experts don’t know how astronauts will survive a trip to Mars without taking in lethal amounts of this cosmic radiation. Elon Musk once suggested that a nuclear-powered spaceship might be less dangerous, because it could drastically shorten travelers’ exposure to this deadly radiation, while exposing them to a smaller amount of also-dangerous nuclear radiation. Musk isn’t a scientist or an expert, but he’s asking the right questions when it comes to the thorny calculus we will need to do if we really want to send people to Mars.
That brings us back to sunscreen, the umbrella term we use for chemicals that absorb and neutralize UV light before it hits our skin, as well as physical barriers that reflect this UV light away. All particles have dimensionality that can physically obstruct radiation, which is just a wave that can only pass through certain things depending on its wavelength. Microwave rays are so wide in wavelength that they can’t escape through the specially prepared window at the front of your microwave oven, for instance. While clouds are by far our best naturally occurring barrier to UV radiation, you should still apply sunscreen.
In space, astronauts are protected by different barriers and generally do not need sunscreen. The ISS has tinted windows that block most UV radiation—clear films that absorb and stop UV rays, protecting the astronauts inside. When they venture outside, astronauts’ spacesuits have extremely strong plastic faceplates that block UV radiation, and the cloth of the suit blocks the rest. It’s believed that just one astronaut has ever received a sunburn, in 1963, when Gene Cernan’s space suit ripped during routine spacecraft maintenance. It seems like he’s lucky he only got a sunburn! And this close call did not discourage him. Nearly ten years later, Cernan became the last person to walk on the moon until, hopefully, NASA’s planned Artemis missions.
Unfortunately, visible-type UV radiation from our own sun isn’t the only game in town when it comes to radiation in space. The key difference is that cosmic radiation, which can come from all over, is what’s known as ionizing radiation, like nuclear and X-ray radiation. This kind of radiation is mostly composed of free-traveling nuclei whose electrons have been peeled off as they travel through space at near light speed; they steal electrons from materials they pass through, like the human body. On Earth’s surface, 5 percent of the radiation we experience every day is this cosmic radiation, but thankfully it’s filtered a great deal, according to the U.S. Environmental Protection Agency. On the ISS, astronauts are just exposed to a lot more of this radiation than they are on Earth, brought down to “as low as reasonably achievable” (ALARA) levels by polyethylene shielding and other measures.
The reason this radiation damages the body so extensively is because of its physical removal of electrons from the body’s molecules. We regularly talk about the cells of the human body like they’re something special, but they’re still made up of atoms like everything else. As ionizing radiation passes through our bodies, it can break apart molecules like DNA, leading to mutations like the out-of-control cell multiplication that defines cancer.
Of course, a lot of risk factors have to line up for that to happen, but NASA says astronauts can be exposed to a dose that is “like if you were to have 150 to 6,000 chest x-rays at a time.” If you buy 6,000 lottery tickets instead of 1, your odds go up quite a bit. If you buy 6,000 tickets for the same lottery each second over eight months, you’re probably going to win.
Before we can safely send people to Mars without an assumed, almost guaranteed risk of cancer and degenerative disease, we’ll need to discover a scientific holy grail: something that blocks ionizing radiation as effectively as today’s sunscreens protect us from UV rays. Because ionizing radiation can pass through everything we know of today, the future of long-haul space travel is still cloudy.
Caroline Delbert is a writer, avid reader, and contributing editor at Pop Mech. She's also an enthusiast of just about everything. Her favorite topics include nuclear energy, cosmology, math of everyday things, and the philosophy of it all.
