A severe meteor storm expected to peak in November will bombard the world?s satellites with an unusually dense amount of space dust, creating the greatest threat of a meteor impact since 1966, according to NASA scientists.

The Leonid meteor shower occurs annually but this year it is expected to be a storm unlike anything seen in recent decades. The last time the Leonids produced what astronomers call a storm, only a handful of satellites orbited the Earth, so the threat was minimal.

Now there are hundreds of satellites that will be at risk. They provide services ranging from pagers and television to weather forecasts and monitoring for potential nuclear blasts from other nations.

Forecasts for the number of meteors per hour during this year?s peak on Nov. 18 range from 1,400 to 15,000. The large disparity in the number of meteors expected reflects the different prediction methods used by various scientists.

Leonid meteors are bits of a comet that are no larger than a grain of sand. They vaporize when they zoom through Earth?s atmosphere at 260 times the speed of sound, looking like shooting stars from the ground. If they hit a satellite, the small grains can destroy an imaging mirror, plow right through fragile parts or, worse, create electrical shorts that can disable the craft. The force of the impact itself can throw a satellite off course.

Bill Cooke of NASA?s Marshall Space Flight Center says that the odds of a satellite being damaged during the peak hours of the Leonid meteor shower are between 1-in-10,000 and 1-in-1,000. At least one satellite could be significantly damaged during the upcoming storm, which will last for several days.

In order to avoid satellite damage, many satellites will be put into hibernation during the storm. They will also be rotated to turn their slimmest profiles into the oncoming stream of meteors. Telescopes like the Hubble Space Telescope are designed to be maneuvered frequently and easily, while some smaller satellites are not.

?We discovered in 1999 [the last time a heavy Leonids meteor shower was predicted] that people batten down the hatches and ride things out,? Cooke says. ?If you?ve done this, there ain?t much more you can do.? Satellites emerged unscathed in 1999, but the risk is five to 10 times greater this year. For several hours around the peak, roughly ten meteors will fill every square kilometer (0.62 miles) of sky at any given moment.

The Leonids are caused by dust and debris left behind by the comet Tempel-Tuttle, which passes through the inner solar system every 33 years. The debris is burned off the comet?s nucleus by a wind of charged particles that stream outward from the Sun. Because Tempel-Tuttle orbits the Sun in the opposite direction compared to Earth, its debris will hit a satellite with much greater velocity than meteors created by the debris from other comets. ?It?s like two cars hitting head-on,? Cooke says.

The greatest danger is the generation of a plasma cloud that could cause an electrical short circuit. When a meteor as fast as a Leonid strikes something, it vaporizes, creating a cloud of plasma, or electrically charged particles. An electrical current can then flow through the plasma cloud from one part of the craft to another, and destroy an instrument on another part of the craft.

In 1993, during the August Perseid meteor shower, a meteor hit an Olympus communications satellite. The impact formed a plasma cloud, and the craft?s control system was zapped. By the time operators could stabilize it, it was too late and the satellite was lost.

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