Health Threat From Cosmic Rays - Human Health Effects

Human Health Effects

The potential acute and chronic health effects of space radiation, as with other ionizing radiation exposures, involve both direct damage to DNA and indirect effects due to generation of reactive oxygen species. Acute (or early radiation) effects result from high radiation doses, and these are most likely to occur after solar particle events (SPEs). Likely chronic effects of space radiation exposure include both stochastic events such as radiation carcinogenesis and deterministic degenerative tissue effects. To date, however, the only pathology associated with space radiation exposure is a higher risk for radiation cataract among the astronaut corps.

The health threat depends on the flux, energy spectrum, and nuclear composition of the radiation. The flux and energy spectrum depend on a variety of factors: short-term solar weather, long-term trends (such as an apparent increase since the 1950s), and position in the sun's magnetic field. These factors are incompletely understood. The Mars Radiation Environment Experiment (MARIE) was launched in 2001 in order to collect more data. Estimates are that humans unshielded in interplanetary space would receive annually roughly 400 to 900 milliSieverts (mSv) (compared to 2.4 mSv on Earth) and that a Mars mission (12 months in flight and 18 months on Mars) might expose shielded astronauts to ~500 to 1000 mSv. These doses approach the 1 to 4 Sv career limits advised by the National Council on Radiation Protection and Measurements for Low Earth orbit activities.

The quantitative biological effects of cosmic rays are poorly known, and are the subject of ongoing research. Several experiments, both in space and on Earth, are being carried out to evaluate the exact degree of danger. Recent experiments at Brookhaven National Laboratory's NASA Space Radiation Laboratory (NSRL) suggest that biological damage due to a given exposure is actually about half what was previously estimated: specifically, it turns out that low energy protons cause more damage than high energy ones. This is explained by the fact that slower particles have more time to interact with molecules in the body.