Jan 24, 2000

Yukon Meteor Blast

image courtesy of Ewald Lemke, Atlin Realty
January 25, 2000 -- Last week, one of the most dramatic meteors in 10 years streaked across the skies of the Yukon Territory in Canada. Witnesses reported two sonic booms, a foul odor, and sizzling sounds heard all the way from Alaska through northwestern Canada. Based on readings from defense satellites and seismic monitoring stations, scientists estimate that the meteor detonated with the energy of two to three kilotons of TNT.

Above: This sequence of pictures was captured by Ewald Lemke (Atlin Realty, Atlin, British Columbia). It shows the expanding smoke train of the Yukon meteor over a 14 minute period. The first frame shows a smoky red vapor trail just 1 minute and 30 seconds after the initial flash.

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"I have never seen anything quite like this before," said Joe Clarke of Marshlake, Yukon, who saw the meteor at 0845 PST (1645 UT) on January 18. "When it started, the flash lit up the mountains 15 km away as bright as daylight, then it just drifted across the sky. The contrail looked to me like the ones left by shuttle launches. It just hung there for at least 1/2 hour. [It's the] wildest thing I could ever imagine seeing."

There was no major meteor shower on January 18. The Yukon fireball was probably what astronomers call a sporadic meteor. The inner solar system is filled with tiny dust particles that have bubbled off innumerable comets as they pass close to the Sun. These particles, called meteoroids, hit the Earth from random directions producing 2 or 3 sporadic meteors per hour every night.

Scientists from NASA and the Department of Defense are interested in the the Yukon event. Samples of dust or rock fragments from the explosion could reveal the origin of the meteoroid. Defense specialists would also like to know what the meteoroid was made of to help calibrate the sensors they used to detect the fireball.

ER-2 airborne sciences aircraft
On Friday, January 21 -- just three days after the explosion -- an Airborne Sciences ER-2 aircraft from NASA's Dryden Flight Research Center flew to the Yukon Territory of northwestern Canada in an effort to collect atmospheric samples of the meteor's lingering debris trail. The region, near the town of Carcross, is mostly unpopulated.

Left: The Airborne Science ER-2 aircraft are platforms for a variety of high-altitude science missions. They are used for earth science and atmospheric sensor research and development, satellite calibration and data validation, and now for catching meteoroids.

Scientists gathered samples of the debris cloud at an altitude of 65,000 feet with an instrument called the Aerosol Particulate Sampler (APS). The APS is a system of two small five-inch by four-inch paddles that deploy simultaneously from the ER-2's left wingtip. The paddles are coated with a silicon oil that collects particles from the high altitude air stream. After a period of exposure, the paddles are withdrawn into hermetic enclosures that prevent contamination during the aircraft's return to Dryden. The paddles will be removed and sent to NASA's Johnson Space Center in Houston, Texas for analysis.

The ER-2 also carried a camera capable of taking black and white photos of eight-mile wide swaths of the region in an effort to locate any impact craters and other scarring of the earth, such as flattened areas of forest, that may have been caused by the explosion and impact of meteorites that separated from the meteor.

Tunguska explosion effects showing stripped and fallen trees
On June 30, 1908, a huge explosion occurred in the sky above the central Siberian wilderness near the Tunguska River in Russia. The concussion from the blast, estimated at 20 megatons of TNT, leveled trees in an area nearly 40 miles in diameter. Oddly, the explosion produced no crater or other evidence of impact.

Right: Trees were incinerated in a 9-mile (14.4 km) radius from ground zero and were knocked over in a 25 mile (40 km) radius following the Tunguska explosion in 1908. If this had occurred over a heavily populated area, the effect would have been catastrophic for the people living there. Image Credit: Smithsonian Institution.

Scientists at NASA and the University of Wisconsin conducted a computer simulation that strongly suggests that the Tunguska culprit was an asteroid, the most common class of meteorite. The simulation indicated that an asteroid about 100 feet in diameter and moving at a speed of 10 miles per second would disintegrate at a height of about five miles above the ground - approximately the same altitude at which the Tunguska object is believed to have exploded. Information gleaned from the January 18 meteorite in Canada might enhance understanding of the Tunguska event.Web Links


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