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(meteorobs) Excerpt from "NEO News (07/03/01) July 23 fireball"




------- Forwarded Message

Date: Fri, 3 Aug 2001 16:03:26 -0700
To: david.morrison@arc.nasadot gov
From: David Morrison <dmorrison@arc.nasadot gov>
Subject: NEO News (07/03/01) July 23 fireball

NEO News (07/03/01) July 23 fireball

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NORTHEAST FIREBALL PINPOINTED (from Sky & Telescope, August 3)

It now appears that July 23rd's dazzling daylight fireball punched
through the atmosphere over central Pennsylvania and may have
scattered meteorites over the rugged woodlands of Sproul State Forest.
Defense Department satellites tracked the meteoroid's flare for
several seconds beginning at 6:19:11 Eastern Daylight Time. The path
began over Scranton (75.6 deg. W, 41.5 deg. N) and ended 140
kilometers to the west over the town of Williamsport (77.3 deg. W,
41.3 deg. N), during which it dropped in altitude from 82 to 32 km.
Despite occurring in daylight, the meteor was bright enough to be
spotted by eyewitnesses from Canada to Virginia.

In its final moments the fireball created a deafening sonic boom that
shook the ground. Meteor expert Peter Brown (Los Alamos National
Laboratory), who is analyzing the satellite records, told Sky &
Telescope, "I can almost guarantee that this object broke up." He says
that reconstructing the object's orbit and flight path are proving
difficult because the entry velocity is uncertain, though it's
probably in the "asteroidal" range of 17 to 20 km per second. Brown
believes that whatever remains of the incoming object probably fell in
an elongated pattern up to 30 km long.

The meteoroid's size is also still a guess. The satellites' visible
and infrared sensors recorded 1.3 billion joules of luminous energy,
which corresponds to a kinetic-energy wallop equivalent to 3,000 tons
of TNT (one-fifth that of the Hiroshima bomb). Meteoroids in this
energy range strike Earth roughly 10 times each year. If it was stony,
as most meteorites are, such an object would have weighed 30 to 90
tons and been the size of a car. However, Brown says acoustic and
seismic data argue for much less kinetic energy and, in turn, a much
smaller object. "I'd hoped to have had some meteorites recovered by
now," Brown concludes, but the many uncertainties diminish that
possibility. "That's why I'm here in New Mexico instead of heading for
Pennsylvania."

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