[meteorite-list] Chicago's Rain of Meteorites

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:10:11 2004
Message-ID: <200304221543.IAA04466_at_zagami.jpl.nasa.gov>

http://skyandtelescope.com/news/current/article_936_1.asp

Chicago's Rain of Meteorites
By Peter Brown
Sky & Telescope
April 21, 2003

On the night of March 26th, shortly before midnight,
residents of several Midwestern states witnessed a dazzling - and, to many,
frightening - spectacle in the sky. A brilliant fireball appeared over
central Illinois and moved north, ending its fiery descent through the
atmosphere in at least two bright flashes just south of Chicago. Powerful
sonic booms soon shook the landscape and were detected as far away as
western Canada.

Shortly thereafter, many people in the suburban town of Park Forest awoke to
the sound of rocks clattering down on their neighborhoods. Paul Sipiera
(William Rainey Harper College) and James Schwade (Planetary Studies
Foundation) have been mapping the extent of the meteorite fall. "At least
six houses and three cars in the town of Park Forest and surrounding area
were damaged," Sipiera says. He estimates that the debris fell in an
elliptical-shaped strewnfield approximately 10 kilometers long and several
wide.

Residents have found meteorites on roads, on lawns, and in woods. One
3-kilogram chunk crashed through a resident's roof and kitchen floor,
bounced off the basement floor, and landed on a table. A slighly smaller
fragment fell through a roof, hit a window and shredded its venetian blind,
bounced off the windowsill, and finally destroyed a large mirror - narrowly
missing a sleeping teenager.

The original body may have been nearly as big as a car before it broke apart
in the upper atmosphere. Steve Simon, a meteorite specialist at the
University of Chicago, says it was a relatively common type of ordinary
(rocky) chondrite classified as L5. Some of the fragments consist of ancient
impact melt, suggesting that the incoming object may have originated near
the surface of its parent asteroid.

Ultralow-frequency sound measurements made 1,100 km away in Manitoba
indicate that the fireball released the kinetic-energy equivalent of 0.5 to
1 kiloton of TNT, much more than conventional explosives but much less than
most atomic bombs. If the meteoroid arrived with a velocity typical of
objects from the asteroid belt, then it probably weighed 10 to 25 tons and
was about 2 meters in diameter. Meteoroids this size hit Earth about a half
dozen times per year but rarely over thickly settled areas. Park Forest (the
event's provisional name) is the largest meteorite fall in the United States
in the last five years and the first to drop hundreds of fragments over a
major urban area.

Analysts have collected several videos recording the bolide's motion. If
additional videos from other viewing angles can be found, it should be
possible to determine an accurate orbit for the wayward object before it
encountered Earth. Therefore, anyone with such videos or other accurate
positional data should contact me. Success would make Park Forest only the
eighth meteorite with an accurate, instrumentally determined orbit.

Peter Brown chairs the meteor physics group at the University of Western
Ontario.
Received on Tue 22 Apr 2003 11:43:32 AM PDT