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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