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Astronomers debate effects of meteor event on satellites
Monday, October 12, 1998 By Michael Woods, Post-Gazette Washington Bureau
Earth is moving inexorably this fall toward a collision with a dense stream of interplanetary debris. Though of no danger to life, the encounter does threaten the life lines of modern technological society: Communications, weather, and spy satellites.
The Leonid meteors are coming. It's 36 days and counting.
The Leonids are a celestial river of rocky particles, most smaller than a grain of sand, left in the trail of Comet Temple-Tuttle each time it swings past the sun. Solar energy heats the comet's core, spinning off an immense cloud of dust that lingers in the comet's orbit.
Every November, Earth's own orbit crosses paths with the debris and fragments collide with the upper atmosphere at a speed of 44 miles per second. Friction heats them to a white-hot glow, visible as "shooting stars." From Earth, the particles appear to originate in the constellation Leo, hence the name Leonids.
The coming encounter is unusual because on Feb. 28 Comet Temple-Tuttle made its closest approach to the sun in 33 years, adding a new batch of debris to the detritus of previous passages.
Comet Temple-Tuttle's last close passage to the sun was in 1966, when some observers saw more than 100,000 meteorites per hour.
Although some astronomers believe the real pelting won't happen until 1999, others say it will occur next month, beginning with a noticeable increase in shooting stars in the evening sky around Nov. 14. The show would peak Nov. 17 and end Nov. 20.
William H. Ailor, director of the Center for Orbital and Reentry Debris Study at Aerospace Corp. of El Segundo, Calif., predicts the Leonid stream will "sandblast" more than 500 communications, weather, and spy satellites.
But Ailor admits that predicting the Leonids' intensity is a guessing game. It may prove little different than a dozen other meteor showers that pelt Earth largely unnoticed each year.
"My own personal opinion is that we shall not see much in the way of a meteor storm," said Brian G. Marsden, an astronomer at the Smithsonian Astrophysical Observatory in Cambridge, Mass. "From an astronomical point of view, it would be nice if I am wrong. From the point of view of communications satellites, I suppose we should be aware that there is some slight possibility of damage."
Don Yeomans, of NASA's Jet Propulsion Laboratory in Pasadena, Calif., expressed similar sentiments.
"If history is any guide, the peak Leonid shower rates will not approach the storm levels noted in 1966," Yeomans said. In November, Earth will pass through the Leonid stream in a position similar to its 1966 passage.
The 100,000 meteors per hour reported during the 1966 storm were much more than had been expected.
"On the other hand, Mother Nature has often pulled the rug out from under astronomers who would be so bold as to predict what should be expected from the Leonid meteor shower," he said.
Iwan Williams, a meteor expert at Queen Mary College in the United Kingdom, said that even a very intense storm still would mean that just a few Leonid meteors strike each square mile of space above Earth. But the total area of all orbiting satellites, he added, probably equals one square mile.
"So there is a reasonable chance that one satellite will be hit, and some chance that a small number will be hit," he said. "This is real bad news if it is your satellite that will be hit. But it is OK if it is somebody else's. Odds are it will be somebody else's."
The uncertainty and potential impact of loss of even a few satellites is fueling rising anxiety.
Last spring, for instance, 40 million pagers stopped beeping, self-service gasoline pumps refused to accept credit cards and TV stations lost programming when a single satellite, PanAmSat Corporation's Galaxy IV, spun out of control.
Much of the rising hullabaloo over the Leonids began last April, when Ailor convened a conference of international meteor experts, and owners of communications satellites. The participants concluded it is unlikely the meteor shower will have a major effect on communications satellites, but recommended that, during the shower, satellite operators have on duty teams of controllers trained to handle meteor impacts.
Satellite owners are concerned not just with a meteor blasting a gaping hole in a satellite. Meteor impacts also can vaporize aluminum and other material on the satellite's surface, creating plumes of plasma -- electrically charged gas. These plasmas could induce stray electrical charges inside the satellite, zapping its circuitry.
The Leonids are especially effective in creating these electrical charges because they are fast-moving, and strike a satellite surface with unusual energy.
These stray electrical charges were blamed for the only documented case of a satellite lost to a meteor impact. It came in August 1993, when four meteors from the annual Perseid meteor shower hit the European Space Agency's Olympus satellite in a span of about 2 minutes.
The conference made other recommendations to protect satellites during the Leonid encounter. These included powering-down some electronic components, monitoring frequently for electrical abnormalities, and reorienting satellites so that sensitive components point away from the oncoming stream of particles.
NASA, for instance, will reorient the Hubble Space Telescope so that its back is pointing toward the particles, rather than its delicate lens and solar panels.
David Meisel of the State University of New York at Geneseo said scientists suspect that meteor showers may play a larger-than-expected role in satellite failures. Satellites other than Olympus have failed during meteor showers, but there was no direct evidence of an impact, he added.
NASA and the U.S. Air Force hope next month's Leonid shower will help settle this question. They have assembled an international team of scientists to collect data from a research aircraft during the shower.
November 1998 and 1999 may the last chances in a lifetime to see a major Leonid storm. Calculations indicate that Jupiter's gravitational pull will alter Comet Temple-Tuttle's orbit in 2029, so that it moves farther away from Earth.
To see the Leonids: Find a dark site unobstructed by trees or buildings, dress warmly and bring a reclining chair. Start watching about 50 degrees up the eastern sky around 1 or 2 a.m. Nov. 17 or Nov. 18. Best viewing may occur in the hour or two before dawn.
For more information, check the Sky & Telescope website.
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