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Mars Exposed to Dangerous Levels of Space Radiation - 2003-03-14

Travelers to Mars, beware! A U.S. satellite orbiting the Red Planet shows that space radiation reaching Mars is very intense. This poses severe health risks for future human explorers.

Information from the Mars Odyssey spacecraft shows that the U.S. space agency NASA will have to take strong measures to shield visitors from the radiation that is pelting the planet.

The Odyssey has been collecting data on various aspects of the Martian environment for one year. One of the scientists examining the radiation readings says they confirm expectations that Mars is a dangerous place for people to be.

"The reason we're doing these measurements is with a long-term eye towards human exploration of Mars because space radiation presents a health hazard," said Cary Zeitlin of the National Space Biomedical Research Institute in Houston.

He said an astronaut could get as much cancer-causing radiation during a three-year mission to Mars as NASA allows during an entire space career. Mr. Zeitlin notes that the annual dose at Mars is 2.5 times more than hits the International Space Station in low-Earth orbit. It is also up to 1,000 times the natural background radiation on Earth.

"Those doses are much higher than anyone would receive at the surface of Earth," he said. "So it certainly is something that future mission planners have to be concerned about, how to mitigate the risk from radiation."

Radiation bombards Mars from the Sun and from unknown sources in our galaxy. It also hits Earth, but our atmosphere protects us from most of it. The Martian atmosphere is too thin to offer the same protection.

The solar radiation varies in intensity over an 11-year cycle. Mr. Zeitlin says that at its peak at the end of the cycle, bursts of charged solar particles can provide a short-term, acute health hazard to space travelers. Those can often last a full week and would be the more worrisome of the two radiation sources.

"These are unpredictable and variable events that come when there is activity on the Sun that produce sometimes very intense flows of particles out into the solar system, particularly into the inner solar system," he said.

In contrast, Mr. Zeitlin says the steady stream of general galactic radiation is of lower intensity, but nevertheless would still present a long-term danger to humans on Mars.

U.S., European and Japanese satellites are all studying the Sun and some of them measure solar storms that generate the charged particle bombardment of the planets. They are giving scientists a better ability to predict such solar activity and to warn of blasts that, although not dangerous as radiation to people, can affect Earth's magnetic field and disrupt the electrical power grid. Presumably, such forecasts could also alert future Mars visitors. Mr. Zeitlin says the radiation is manageable if they have special shelters for refuge.