EP-TOMS LEONIDS SHUTDOWN UPDATE

The Earth Probe TOMS was shut down on November 17 for 24 hours starting at 4 am EDT. TOMS was brought back on-line at 10 am EDT during the Poker Flat Pass. This was done to insure the safety of the instrument during the Leonid meteor shower.

The Leonid meteor shower raised concerns about satellite safety because the particles were moving at such high velocities. The Leonids are in a retrograde orbit (opposite to the Earth's orbit) so they hit nearly head-on, with a relative velocity of 71 km/sec (155,000 mph). At that velocity, even small dust particles (between 1-100 microns) can create a plasma cloud upon impact, producing a significant risk of electrical short.

The source of the material making up the Leonid swarm is comet Tempel-Tuttle. The comet's orbital period is 33.25 years and produces a maximum debris trail in the year following its perihelion or closest approach to the sun. The comet produced giant showers in 1833 and in 1966. In 1998 the meteor swarm crossed the Earth's orbit near the L1 point, approximately 1.2 million km from Earth. The main swarm was approximately 200,000 km in diameter.