Astronauts traveling to Mars will get hit with long-term, low-dosage radiation. A new study in mice suggests the radiation could cause lasting memory and learning problems. (Credit: u3D/Shutterstock)

There’s a major outstanding question lingering over the future of human spaceflight: Just how much radiation can the body handle? While humans have spent more than a year at a time on orbiting space stations without ill effect from radiation, almost all astronaut experience has been in low-Earth