It's Coming, Earth: Cosmic Buckshot

By Mike Toner
Journal-Constitution Staff Writer

A cloud of cometary debris is on a collision course with Earth. There will be no escape. The date - even the hour - of the impact are certain. And in most cases, earthlings will be able to do little but watch.

The collision will come later this year, on the night of Nov. 17 and in the early hours of the 18th. The space shuttle will be grounded. The Hubble Space Telescope will be buttoned up in its safest "nuclear attack" mode. Faced with the certainty of the impending collision, scientists and engineers will huddle in California this coming week to ponder what else can be done to limit the damage.

No, this is not a promo for Hollywood's next "sky is falling" flick. Killer asteroids hurtle from Hollywood's skies like cannon shots. The real-life threat that worries aerospace experts will be more like a blast of hypersonic buckshot. Most of the incoming debris will burn up in the atmosphere. High above the atmosphere, however, hundreds of orbiting satellites lie directly in harm's way.

In mid-November, as it does every year, Earth will sweep through the debris field of the comet Tempel-Tuttle, encountering the cloud of comet dust that produces the annual Leonid meteor shower. But this year, for the first time since 1966, Earth will pass through the densest portion of Tempel-Tuttle's debris stream. Instead of the 12 meteors an hour that normally light up the sky during the annual mid-November Leonid meteor shower, the Earth could be pelted by a storm of tiny meteors - at rates that could range from 1,000 to more than 100,000 an hour. For casual observers, the Leonid meteors - so named because they appear to radiate from the "head" of the constellation Leo the Lion - will simply be a rare visual spectacle. But to a world that has become dependent on orbiting satellites for vital communications, weather, research and defense since the last major Leonid storm in 1966, the cloud of flying buckshot is a potential headache of cosmic proportions.

"We've never faced a situation like this before," says B. Jeffrey Anderson, an aerospace engineer at NASA's Marshall Space Flight Center in Huntsville, Ala.

"Back in 1966, we only had a handful of satellites in space," Anderson says. "Today we have more than 400 operational satellites and we would not be surprised to see two or three of them damaged or destroyed by Leonid debris."

Compared to the doomsday rocks destined to star in this summer's celluloid blockbusters - Disney's "Armageddon" and Dream Works' "Deep Impact" - the Leonid meteors are small potatoes. Most of the particles in the dust cloud trailing comet Tempel-Tuttle are smaller than grains of beach sand.

But what they lack in size they make up for in speed. Because the Earth and the debris swarm will be approaching each other like oncoming trains, they will collide at velocities totaling more than 150,000 mph.

"Because of the high velocities caused by hitting the Leonid stream head on, even something as small as a grain of sand will have the kinetic energy of a .22 caliber bullet," says William Ailor, director of the center for orbital debris of Aerospace Corp., which is hosting the April 27-28 summit of space experts in Manhattan Beach, Calif.

Even in the vastness of space, the prospect of tens of thousands of .22 caliber bullets zipping through space amid vital communications, weather and defense satellites gives engineers, satellite operators and insurance companies the willies.

"The problem is that anything moving this fast, regardless of size, that hits a satellite is likely to generate a plasma -- an electrically charged gas -- that could damage or destroy vital electronic components," says William Cooke, a researcher with Computer Sciences Corp., a contractor with NASA's Huntsville space center. "Even something as small as a grain of sand could fry a multi- million dollar satellite."

Even if the electrical disruption is temporary, it could have lasting consequences. In 1993 a small meteor hit the European Olympus telecommunications satellite, temporarily knocking out the software that kept it in a stable orbit. By the time ground controllers regained control, the satellite's fuel had been exhausted, rendering it virtually useless.

The number of potential targets is growing rapidly. Within the last year, for instance, a consortium of companies headed by Motorola Inc. has launched 56 communications satellites as part of an orbiting mobile telephone network. Hundreds of other satellites for similar networks have either been placed in space or soon will be.

"If one of the satellites hit by the Leonids should happen to be knocked out of orbit and damage something, the owner would be absolutely liable for any damage that occurred," says Delbert Smith, senior partner in the Washington law firm of Reed, Smith, Shaw and McClay, which specializes in aerospace issues.

"When I first raised this issue at a conference a few years ago I was uniformly hooted down," Smith says. "Today, a lot of people are taking the Leonid threat very seriously."

But engineers say there isn't a lot that satellite operators can do. The Earth may shield a few of them from the debris as it sweeps through the dust cloud. But because there are so many small, untrackable specks moving so fast, dodging them is impossible.

"Many commercial operators will probably opt to do what the military is already planning to do," says NASA's Anderson. "They're going to shut down all non-critical systems and rotate some of their satellites so that they present the smallest area to the incoming stream of particles. Beyond that, they can only hope for the best."

There is a wide range of uncertainty about the size of the threat. On a typical evening, the number of visible meteors average three to four an hour. During a typical Leonid shower, the rate may reach 12 per hour.

But last November, in what many astronomers say may have been a prelude to this year's event, the rate of visible meteors peaked at more than 150 an hour as Earth swept through a slightly denser portion of the Temple-Tuttle cloud.

During the last full-fledged Leonid storm in 1966, however, the rate reached an astonishing 150,000 meteors an hour -- and historical accounts of previous storms, including those in 1799 and 1833, suggest that such outbursts are not unprecedented.

Current thinking among astronomers is that November's storm will probably produce peak rates of less than 10,000 meteors an hour.

"A rate like that would not probably wreak havoc on our satellite systems, but if operators decide to power down, there could be some service disruptions," Cooke says. "It's possible that we won't see any permanent damage. But if we don't lose a couple of satellites, it will be due, at least in part, to luck."

They may need it. Some astronomers say the Earth won't encounter the densest portions of the dust cloud until November 1999, or even November 2000. And if the Leonids don't do any harm, there are dozens of other less predictable debris clouds -- the Draconids, Lyrids, Perseids, Andromedids - that periodically pelt the Earth.

"The Leonid meteor storm should be a reminder to all of us that space is not always the dark and empty place that it seems to be," says attorney Smith. "It may be dark, but it's not empty."