NASA Prepares For "Last Chance" Meteor Shower

"Even with the full Moon, this year's Leonids will probably be better than any other for the next hundred years," said Dr. Don Yeomans, an astronomer at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "If you're ever going to see them, this might be the year to try." NASA is taking advantage of the event for several research efforts around the world.

The shower is predicted to have two peaks, each a couple of hours long, during which the most meteors can be seen. The shower's second peak, most prominent in North American skies, is expected at around 2:30 a.m. (Pacific time) Nov. 19, and promises the rare spectacle of a few meteors every minute or even more. "Observers in good locations away from city lights might see a few hundred per hour. You'll only get to see the bright ones because the moonlight will wash out the ones that aren't as bright," said Yeomans. Last year, observers did not have to contend with the Moon and saw meteors at a pace of several hundred per hour.

An earlier peak is expected over Europe and Africa the night of Nov. 18, and observers in North America might see a few grazers -- meteors skimming the top of the atmosphere -- from this first peak starting around 8:30 p.m. (Pacific time) Nov. 18.

The Leonids are grains of dust from comet Tempel-Tuttle colliding into Earth's atmosphere. Most Leonid particles are tiny and will vaporize very high in the atmosphere due to their extreme speed (about 71 kilometers or 44 miles per second), so they present no threat to people on the ground or even in airplanes. As it progresses in its 33-year orbit, the comet releases dust particles every time it comes near the Sun. Earth intersects the comet's debris trail every year in mid-November, but the intensity of each year's Leonid meteor shower depends on whether Earth ploughs through a particularly concentrated stream of dust within the broader debris trail.

The dust that Tempel-Tuttle shed in 1866 makes up the stream predicted to give Americans a good show this year. Last year, people in Asia saw the plentiful collisions within that stream. A dust stream from 1767 provided last year's peak hour of viewing in North America and will provide this year's peak hour of viewing in Europe. After 2002, Earth won't hit either of those streams again for decades to come, and is not predicted to encounter a dense Leonid stream until 2098 or 2131.

The golden rule for watching the Leonids -- or any meteor shower -- is to be comfortable. Be sure to wrap up warmly -- a sleeping bag placed atop a lawn chair facing east is a good way to enjoy the show. Put your chair in a clear, dark place with a view of as much of the sky as possible. Don't stare at any one place. Keep your eyes moving across the sky. Most Leonids will appear as fleeting streaks of light, but watch for the bigger ones that produce fireballs and trails. Some trails will remain visible for several minutes or more.

The Leonids get their name from the constellation where they appear to originate; the meteors will be radiating from the Sickle pattern in the constellation Leo the Lion, which will be rising out of the east-northeast sky. Don't look directly at the constellation, but at the area above and around it. And, though you don't need them to see the Leonids, a pair of binoculars could come in handy.

Researchers think meteors might have showered the Earth with the molecules necessary for life's origin. A two-aircraft campaign, led by astronomer Dr. Peter Jenniskens of the SETI Institute and NASA's Ames Research Center, Moffett Field, Calif., will investigate this possibility. "We are looking for clues about the diversity of comets and their impact on the chemistry of life's origin on Earth," Jenniskens said.

"We are eager to get another chance to find clues to two puzzling questions: What material from space rains down on Earth, and what happens to the (meteor's) organic matter when it interacts with the atmosphere?" said Dr. Michael Meyer, senior scientist for astrobiology at NASA Headquarters, Washington, D.C.

On Nov. 15, a team of 42 astrobiologists from seven countries will depart from southern California's Edwards Air Force Base on a mission to Spain to observe this year's two Leonid storm peaks. The DC-8 Airborne Laboratory, operated by NASA's Dryden Flight Research Center, Edwards, Calif., will carry high-speed cameras; a radio receiver to listen to upper atmosphere molecules; and a team of meteor observers, who will keep track of the meteor activity for satellite operators concerned about impact hazards.

"This final deployment of the Leonid Multi-instrument Airborne Campaign program promises an important and unique database for the development of instruments targeted at in situ sampling of cometary materials and for the future definition of comet missions," said Dr. John Hillman, lead scientist for planetary astronomy at NASA Headquarters. "It is hoped that these scientific data will provide new insights for the comparative studies of comets."

Although the meteors are harmless to people, there is a slight chance that a satellite could be damaged if it was hit by a Leonid meteoroid. The meteoroids are too small to simply blow up a satellite. However, the Leonids are moving so fast they vaporize on impact, forming a cloud of electrified gas called plasma. Since plasma can carry an electric current, there is a risk that a Leonid-generated plasma cloud could cause a short circuit in a satellite, damaging sensitive electronic components.

NASA's Goddard Space Flight Center, Greenbelt, Md., is responsible for controlling a large number of satellites for NASA and other organizations and is taking precautions to mitigate the risk posed by the Leonids. These include pointing instrument apertures away from the direction of the Leonid stream, closing the doors on instruments where possible, turning down high voltages on systems to decrease the risk of a short circuit, and positioning satellites to minimize the cross-section exposed to the Leonids.

Minimizing the threat meteoroids pose to satellites is the second major area of NASA's Leonid research. From five key points on the globe and from the International Space Station, NASA researchers will use special cameras to scan the skies and report activity around the clock during the Leonid shower. Led by Dr. Rob Suggs of the engineering directorate at NASA's Marshall Space Flight Center in Huntsville, Ala., the research is part of a long-term goal to protect spacecraft from potentially damaging meteoroids.

Using "night-vision" image-intensifier video systems and sky-watchers outfitted with Palm computer software developed to record visual counts, NASA engineers and astronomers will record their observations for later analysis. Another tool at Marshall's disposal is "forward-scatter radar" -- an early warning system built by Suggs, Dr. Jeff Anderson, also of Marshall's engineering directorate, and Dr. Bill Cooke, an astronomer at Marshall.

"Our system is pretty simple," said Suggs. "We use an antenna and a computer-controlled shortwave receiver to listen for 67 megahertz signals from distant TV stations." The transmitters are over the horizon and normally out of range. When a meteor streaks overhead, the system records a brief ping -- the echo of a TV signal bouncing off the meteor's trail. Like the image-intensified cameras, this system is capable of detecting meteors too dim to see with the unaided eye.

The research data from the Leonids shower will be analyzed to help NASA engineers refine their forecasts for spacecraft; by better determining where, when and how the meteors will strike, NASA can improve protective measures to prevent or minimize damage to spacecraft.

For more information, including predicted peak times for major cities and NASA media contacts, refer to http://www.gsfc.nasa.gov/topstory/2002/1114leonid.html.