SPACE.com -- Mars Odyssey Shows Intense, But Managable Radiation Risk for Astronauts

Data from Odyssey's Martian radiation environment experiment show that the radiation dose equivalent at Mars is two to three times greater than that aboard the International Space Station. The differences are primarily due to the magnetic field surrounding the Earth, which provides considerable shielding to astronauts in orbit. Mars lacks a strong magnetic field and is therefore more exposed to the harshest elements of space radiation.

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	Mars Odyssey Shows Intense, But Managable Radiation Risk for Astronauts By Robert Roy Britt Senior Science Writer posted: 03:30 pm ET 13 March 2003

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Preliminary measurements of space radiation at Mars suggest that astronauts who travel there could face exposure to doses that over the course of a three-year mission would approach the lifetime safety limits set by NASA.

While the radiation appears to be manageable, an official said a network of radiation sensors in the inner solar system will be needed to warn Mars astronauts of impending space storms so that they can take cover.

Radiation levels were monitored over the past year by NASA's Odyssey spacecraft and projected to a three-year period, roughly how long a crewed mission to the Red Planet might last.

"It is certainly something that future mission planners are going to have to be concerned about, how to mitigate the risk from radiation," said Cary Zeitlin, the principal investigator for a radiation detection instrument aboard Odyssey.

Zeitlin explained the tentative findings today at a press conference at NASA's Jet Propulsion Laboratory.

Odyssey's Martian Radiation Environment Experiment (MARIE) instrument looks for two types of radiation, in a stated effort to prepare for possible human missions that NASA has yet to formally plan. Mars is continually bombarded by a relatively steady flow of charged particles, from all directions, that are of unknown galactic origin. The planet is also hit by expulsions from the Sun, which occur now and then and can also hit Earth.

Both forms of radiation can have myriad possible health effects in low doses over time.

The radiation is measured in sieverts, and NASA sets lifetime limits for astronauts. The limits vary by age and gender, but generally are between 1 and 3 sieverts and tend to go down as more health studies are done, Zeitlin explained. Odyssey's measurements suggest radiation above Mars is about 2.5 times higher than at International Space Station, he said. Extrapolated to three years, they represent about 1 sievert, he said.

While Earth's strong magnetic field shields the surface from much of this radiation, Mars suffers higher doses at the ground.

"Those are manageable doses," Zeitlin said. However, he added, "it would be close to the limit."

The Odyssey data have confirmed that solar radiation bursts can be very directional, but not always.

When Mars and Earth are on the same side of the Sun, as they will be this summer, a single burst might affect both planets, Zeitlin said, and Odyssey will look for such events. But Mars spends a good portion of time on the opposite side of the Sun, in relation to Earth. During the past year, some solar storms struck only one planet. One storm hit both Earth and Mars last July, when the two planets were on opposite sides.

"We'll have to have radiation monitors around the inner solar system to watch out for these sorts of events and send out warnings, alarms, so astronauts can take appropriate shelter as needed," Zeitlin said.

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