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November 1998
Science

On the trail of Leonids

The NSF/NCAR Electra is expected to join an Air Force KC-135 above Okinawa, Japan in a rare opportunity to document the Leonids meteor shower. Some as bright as Venus, the meteors will race at 160,000 miles per hour (72 kilometers per second) into the earth's upper atmosphere on the night of 17-18 November. The expected storm will occur on the afternoon of the 17th in North America but after midnight near Okinawa.

NASA is heading the Leonid Multi-Instrument Aircraft Campaign, the first mission in the agency's Astrobiology Program. Peter Jenniskens, of the Search for Extraterrestrial Intelligence (SETI) institute and NASA Ames Research Center, conceived of and organized the experiment, which is also supported by NSF, the Air Force, and NHK Japanese television. Also collaborating are five universities, the Ondrejov Observatory (Czech Republic), and the Aerospace Corporation.

The Leonids storm will occur when the earth enters the dense debris behind comet 55P/Tempel-Tuttle over a roughly two-hour span on 17 November and again on 18 November 1999. Although the comet returns every 33 years, some of its visits have been especially noteworthy. In 1966, observers in western North America logged thousands of meteors in a 20-minute period. In 1833, a fantastic swarm of meteors--some reportedly as bright as the moon--may have helped trigger the U.S. religious revivals of the late 1830s and 1840s.

The scientific importance of this experiment hinges on how a meteor's mass compares to its brightness and to the mass of its parent comet. The Electra will carry:

In order to "weigh" a given meteor, researchers will compare its brightness on the NHK camera image to its iron lines on the dual lidar.

The Air Force's KC-135 will circle the Electra in a racetrack pattern between 30,000 and 40,000 feet while the Electra flies back and forth (north-south) within the loop about 10,000 feet lower. Both will be safe from the meteors above, which will burn up 60 to 75 miles (100 to 120 km) above ground. On the night of 23-24 October, an Electra test flight from Jeffco succesfully calibrated instruments while taking advantage of a milder meteor shower, the Orionids, that featured up to ten meteors per hour.

"There's a lot of excitement and a lot of uncertainty, which extends even to the intensity of the event," says Jenniskens. "It could be a light to moderate shower or a full-blown storm." Adds RAF project manager Bruce Morley, "We don't know much about iron in the atmosphere. Observing just one meteor will make a big difference."


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