Iron radiation particles may cause the disease to develop, and NASA currently doesn’t have a way for astronauts to avoid them.

Scientists have found a new potential hazard to space travel: Exposure to radiation in space could cause brain damage and may cause astronauts to develop early-onset Alzheimer’s disease, according to a new study released Monday.

Animals exposed to iron radiation particles that are similar to those caused by exploding stars in space showed neurodegeneration much earlier than would be expected, and the animals’ brains showed plaque associated with Alzheimer’s disease. The radiation levels were similar to levels an astronaut would experience while traveling on a mission to Mars.

Unlike many types of space radiation, the particles associated with iron are able to penetrate a spacecraft’s walls.