It is well-known that deep-space radiation would be risky for future astronauts on long-lasting missions to targets such as Mars, but new research puts the danger in stark relief.

The health risks could include cancer, especially colon cancer, and premature aging, according to preliminary findings from a NASA-funded study of mice which found that so-called high linear-energy-transfer (LET) radiation in space can do more harm to living cells than the low-LET radiation that people encounter more commonly on Earth, said researcher Dr. Albert Fornace, co-investigator at Georgetown University's Lombardi Comprehensive Cancer Center.

"There's some evidence of an increase in oxidative stress and ongoing DNA damage," Fornace said.

The study found that high-energy radiation caused more damage in the gastrointestinal tract of mice than lower-energy gamma or X-ray radiation used in medical therapies. That's because unusually high levels of free radical molecules can injure living cells and lead to runaway genetic mutations which trigger cancer.

Researchers also saw evidence of premature aging in the graying coats of the mice, with similar results having surfaced before in other radiation studies.

Astronauts on proposed long-duration missions to the moon, Mars or beyond would encounter high-energy radiation once outside the Earth's protective magnetic field and endure months of exposure.

High-LET radiation is found in solar flares and is made up of high-energy protons, charged iron particles and some gamma radiation. Earth?s atmosphere blocks the majority of this radiation, preventing exposure to these particles in normal life.

Astronauts on shuttle or space station missions (relatively short-duration missions) sometimes see flashes of light when they close their eyes — the result of high-energy particles striking and probably killing retinal cells in their eyes.

?[W]ith plans for a mission to Mars, we need to understand more about the nature of radiation in space," said lead investigator Dr. Kamal Datta. "There is currently no conclusive information for estimating the risk that astronauts may experience.?

Current astronauts may have a higher risk of cancer than on average, according to a 2004 National Academy of Sciences report. However, the only significant increase in astronaut mortality so far comes from accidents such as the Challenger and Columbia disasters.

Still, the danger of high-energy radiation would currently be too great for astronauts to undertake long-term moon and Mars missions, according to a 2008 report by the National Research Council.

The long-term effects of high-energy radiation may remain unknown, but researchers plan to watch how the test mice develop gastrointestinal tumors over the next year or so. Even a doubled risk of getting gastrointestinal cancer from high-energy radiation could be significant, because gastrointestinal cancers are the most common.

Understanding if high-energy radiation affects living cells the same way as low-energy radiation should help NASA begin to plan around the problem and develop appropriate medical or shielding technologies.

"Making risk estimates should be straightforward if the mechanisms are the same," Fornace told SPACE.com. "We'll be able to plan accordingly with preventative therapies."

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