June 27, 2003: In 1967, NASA’s Mariner 4 spacecraft was cruising through the solar system, not far from Earth, when something unexpected happened.
“Mariner 4 ran into a cloud of space dust,” says Bill Cooke of the Marshall Space Flight Center Space Environments Team. “For about 45 minutes the spacecraft experienced a shower of meteoroids more intense than any Leonid meteor storm we’ve ever seen on Earth.” The impacts ripped away bits of insulation and temporarily changed the craft’s orientation in space.
Fortunately, the damage was slight and the mission’s main objective–a flyby of Mars–had been completed two years earlier. But it could have been worse.
“There are many uncharted dust clouds in interplanetary space. Some are probably quite dense,” says Cooke. Most of these clouds are left behind by comets, others are formed when asteroids run into one another. “We only know about the ones that happen to intersect Earth’s orbit and cause meteor showers such as the Perseids or Leonids.” The Mariner 4 cloud was a big surprise.
“Of all NASA’s Mars spacecraft, Mariner 4 was the only one we’ve sent with a micrometeoroid detector,” he continued. During its journey to Mars and back, the detector registered occasional impacts from interplanetary dust grains–as expected. The space between the planets is sprinkled with dust particles. They’re harmless in small numbers. But when Mariner 4 encountered the cloud “the impact rate soared 10,000 fold,” says Cooke.
