On the big screen, astronauts face many dangers, from explosions, to suffocating in the vacuum of space, to maniacal red-eyed sentient computers. But perhaps the deadliest threat to real astronauts is one they can’t even see: radiation.

Our planet’s magnetic field generates a protective bubble, called the magnetosphere, that shields the surface from damaging cosmic radiation. Humans traveling beyond this bubble will be subjected to dangerous cosmic rays and solar storms, which can damage cells and cause changes in DNA.

Even the shielding currently used on the International Space Station, which is low enough in Earth’s orbit to sit safely inside the magnetosphere, would not be enough to protect pioneering astronauts headed into deep space. A trip to Mars, for