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MARIE, designed to measure radiation, started malfunctioning shortly after a series of strong solar flares occurred in Autumn of 2003

The Martian Radiation Experiment, or MARIE was designed to measure the radiation environment of Mars using an energetic particle spectrometer. It was led by NASA's Johnson Space Center and the science investigation was designed to characterize aspects of the radiation environment both on the way to Mars and while it was in the Martian orbit.

Since space radiation presents an extreme hazard to crews of interplanetary missions the experiment was an attempt to predict anticipated radiation doses that would be experienced by future astronauts and it helped determine possible effects of Martian radiation on human beings.

Space radiation comes from cosmic rays emitted by our local star, the sun, and from stars beyond our solar system as well. Space radiation can trigger cancer and cause damage to the central nervous system. Similar instruments are flown on the Space Shuttles and on the International Space Station (ISS), but none have ever flown outside of Earth's protective magnetosphere, which blocks much of this radiation from reaching the surface of our planet. Ironically, in the Autumn of 2003 after a series of particularly strong solar flares MARIE started malfunctioning, probably as a result of being exposed to the solar flare's intense blast of particle radiation. The instrument was never restored to working order.

A spectrometer inside the instrument measured the energy from two sources of space radiation: galactic cosmic rays (GCR) and solar energetic particles (SEP). As the spacecraft orbited the red planet, the spectrometer swept through the sky and measured the radiation field.

The instrument, with a 68-degree field of view, was designed to collect data continuously during Mars Odyssey's cruise from Earth to Mars. It stored large amounts of data for downlink, and operated throughout the entire science mission.

The Mars Radiation Environment Experiment weighs 3.3 kilograms (7.3 pounds) and uses 7 watts of power. It measures 29.4 centimeters (11.6 inches) by 23.2 centimeters (9.1 inches) by 10.8 centimeters (4.3 inches).

MARIE found that radiation levels in orbit above Mars are 2.5 times higher than at the International Space Station. Levels at the Martian surface might be closer to the level at the ISS. Average in-orbit doses were about 22 millirad per day (220 microgray/day or 0.08 gray/year)). However occasional solar proton events (SPEs) produced much higher doses. SPEs were observed by MARIE that were not observed by sensors near Earth, confirming that SPEs are directional.

• NASA's site on MARIE
• MARIE instrument site at Johnson Space Center