Space Radiation Poses Unknown Risks
By Ilene Raymond Rush
Editor-in-Chief
December 1, 2006
While NASA gears up for a planned 2020 expedition to the moon and a projected 2035 voyage to Mars, one possible deal breaker remains - cosmic radiation.
As spaceships and astronauts voyage beyond the Earth's protective magnetosphere, galactic cosmic radiation - which consists mostly of high-speed charged particles -- can deeply penetrate the body. Effects can range from acute episodes of radiation sickness to long-term problems with cataracts, cancer, sterility, and the central nervous system, as the rays rearrange genetic codes.
Without exact knowledge of the precise nature of cosmic radiation-induced health effects or the amount of exposure astronauts will undergo during long term missions, scientists remain unsure about other short and long-term damage - or how to stop it.
"Radiation isn't the only problem," says Marco Durante, PhD., professor of physics at the University of Federico II in Naples Italy and a researcher in space radiation and cancer. "But it is one of the most serious."
His colleague, Marcelo Vazquez, MD, PhD. who works for NASA and the Brookhaven National Lab agrees.
"It could be a show stopper," says Vazquez.
Unlike earlier missions, the 2020 journey to the lunar surface may last up to 200 days, while the planned Mars voyage may stretch to 3 years, opening up the exciting prospect of new sources of knowledge but also the danger of increased exposure to galactic cosmic rays.
Complicating matters, says Vasquez, is that space radiation, which involves heavy ions and unknown health effects, can only be studied by referring to data on earth radiation. Without first hand experience of the effect of particle showers on astronauts, researchers must extrapolate the effects of outer space radiation or rely on particle accelerators to replicate the effects.
"Our best models of the effects of ionizing radiation are based on what we have learned from survivors of atomic bombs," says Durante. "Luckily for us, the Japanese kept very good records. However, galactic cosmic rays are very different from atomic bomb radiation."
Risk estimates compare figures for an average population based on age-dependent and sex-dependent rates of death, combined with a model of radiation induced cancer mortality rates. But the two big unknowns - the quality of the radiation and the doses of radiation - remain uncertain.
The highest risk to astronauts during a moon mission will come from occasional solar particle events or showers, and adequate shielding may protect visitors. But on Mars, astronauts may be limited to about three hours away from a protected base before they go into a red planet alert from a radiation overexposure. According to an article by Durante and Francis Cucinotta, a NASA researcher in radiation, in the May 2006 issue of Lancet Oncology, on Mars "every cell nucleus in an astronaut's body would be hit by a proton or secondary electron every few days."
Acknowledging these dangers, both Durante and Vazquez note that several possibilities to shield astronauts may yet yield positive results - including drugs, dietary changes, and improved physical uniforms and structures. Yet much remains unknown and unsolved, waiting for further basic research in how the invasion of heavy radiation particles impacts the body's cells.
Given the inherent dangers of space travel, why bother? Both Durante and Vazquez respond to the oft-asked question.
"For knowledge for sure," says Durante. "But exploration is in man's nature and without it, we would not be fully human. It's part of who we are."
For more see:
Cancer risk from exposure to galactic cosmic rays: implications for space exploration by human beings
Cucinotta FA, Durante M
Lancet Oncology - Vol. 7, Issue 5, May 2006, Pages 431-435
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