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Meteorites Don't Pop Corn

A fireball that dazzled Americans on July 23rd
was a piece of a comet or an asteroid, scientists say.
Contrary to reports, however,
it probably didn't scorch any cornfields.

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July 27, 2001
Every few weeks, somewhere on Earth, a fiery light streaks across the sky casting strange shadows and unleashing sonic booms. Astronomers call them fireballs or "bolides." They're unusually bright meteors caused by small asteroids that disintegrate in our planet's atmosphere. Often they explode high in the air like kilotons of TNT -- blasting tiny meteorites far and wide.

It happens all the time, say experts, but usually no one notices. We live on a big planet, after all, and very little of Earth's surface is inhabited by people. Most debris from space falls unseen over oceans or sparsely-populated land areas -- or during times when sky watchers simply aren't paying attention.

A sketch of the 7/23/01 Pennsylvania Bolide, as seen and drawn by witness Richard Weinstein from Wyomissing, PA (angular measurements made with a sextant).
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Last Monday was different, however. On July 23rd hundreds of thousands of people were looking when, unexpected, a fireball appeared over the US east coast. It was 6:15 p.m. local time. The Sun hadn't set, but onlookers had no trouble seeing the fireball in broad daylight. Witnesses from Canada to Virginia agreed that the colorful fireball was brighter than a Full Moon, and some saw a smoky trail lingering long after it had passed.

"Contrary to some reports this was not a meteor shower," says Donald Yeomans, manager of NASA's Near Earth Object program at the Jet Propulsion Laboratory. Meteor showers happen when Earth passes through the debris trails of comets and countless thousands of cosmic dust specks burn up in Earth's atmosphere. At the heart of Monday's fireball, however, was a solitary object -- perhaps a small asteroid or a piece of a comet.

Hundreds of eyewitness reports collected by the American Meteor Society establish that the fireball was moving on an east-west trajectory that carried it directly over the state of Pennsylvania. "It was traveling perhaps 15 km/s (34,000 mph) or faster when it exploded in the atmosphere with the force of about 3 kilotons of TNT," says Bill Cooke, a member of the Space Environments team at the Marshall Space Flight Center. If this was a rocky asteroid, then it probably measured between 1 and 2 meters across and weighed 30 or so metric tons.
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**Editor's Note**
Did you see the July 23rd fireball? If so, please submit a report to the American Meteor Society. They can use your information to refine the trajectory of the meteor and possibly pinpoint the location of meteoritic debris.

Cheers,
Dan