The mission to Mars may be tainted by the possibility that the voyage may result in Alzheimer's or even blindness for the astronauts. Studies where mice have been exposed to stellar radiation have resulted in cognitive degradation. Although, it's possible that a SciFi-like shielding system may protect astronauts of the future.
When traveling in space beyond the protection of Earth's magnetosphere, you are likely to see a strange phenomenon entitled "flicker-flash" by scientists in NASA. In the past, this phenomenon usually occurred during sleep shifts when the spacecraft was dark and the windows were shaded. People would suddenly spot a brief flash, then nothing. Occasionally there were would be streaks, not unlike a tiny meteor trail, and even double flashes.
The first sighting of these events were with the Apollo missions, naturally, since any particles that could do this would normally be deflected by the Van Allen belts. These magnetic belts extend over thirty five thousand miles above the Earth and protect it from all sorts of cosmic radiation.
Flicker-flash was hypothesized at the time to be a high energy subatomic particles of some sort, yet to be determined, that penetrate spacecrafts. A streak of light would appear to the viewer, either the result of the ionization caused by the atmosphere of the spacecraft or an effect solely caused by the particle hitting the eyes' retinas. Research had determined these particles not only penetrated in and out of the spacecraft, but they also penetrated through astronaut's helmets and even heads. Even so, there was no physical sensation connected with the phenomenon at all; it is strictly a visual impression.
Dr. M. Kerry O'Banion, a professor of neurobiology and anatomy at the University of Rochester Medical Center, was part of a study published in PLOS One that looks at the effects of galactic cosmic radiation on mice. For six months, the mice underwent behavioral and memory testing, which showed a decrease in the mice's cognitive abilities. According to CNET, the studies conclusions paint a grim picture for manned space exploration:
"The doses used in this study are comparable to those astronauts will see on a mission to Mars, raising concerns about a heightened chance of debilitating dementia occurring long after the mission is over."
"These findings clearly suggest that exposure to radiation in space has the potential to accelerate the development of Alzheimer's disease."
"Traditional methods for protecting spacecraft and occupants from these forms of radiation involve some configuration of a massive material shield to absorb the energy of incoming particles. For the high energy galactic cosmic rays (GCRs) that astronauts will be exposed to, these so-called passive shields are too massive to be practical and will likely produce showers of secondary radiation that could be more harmful than the GCRs themselves. Active shields which rely on magnetic (or electric) fields to deflect energetic particles offer a potential solution to the problem. Designing a magnetic shield that is strong enough to deflect GCR particles but weak enough to not harm astronauts is a challenge."