There are too many unknown health risks to go to Mars soon
Projecting the health risks to astronauts from exposure to space radiation remains a largely unsolved problem, raising concerns about cancers, circulatory diseases, cataracts and changes to cognition and memory.
The potential harmful effects are qualitatively different from those of exposure to radiation on Earth, like X-rays, since space radiation involves heavy ions and secondary neutrons, which have been shown to induce distinct damage to cells and tissues. While space missions always carry risks, these threats to human health are still not well enough understood to be factored into current risk projection models.
One way to know: Because the current number of astronauts is small and past space missions have been relatively short, research using experimental models at particle accelerators, which can simulate space radiation, is likely our best method to make progress. We now have a solid understanding of shielding materials and space environments, but a sustained biomedical research program of 2000 beam hours per year over a decade, as advocated by the U.S. National Research Council, is still needed to understand the long-term effects of exposure.
The bottom line: Advancements in biophysics, cancer biology, and neuroscience are necessary not only to accurately predict health risks, but also to create biomedical countermeasures and sufficiently understand our genetic vulnerability to the unique types of radiation in space.
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