[meteorite-list] Meteors Come In With A Bang

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:41:54 2004
Message-ID: <200101051634.IAA26852_at_zagami.jpl.nasa.gov>

http://helix.nature.com/nsu/010104/010104-8.html

Meteors come in with a bang
By PHILIP BALL
Nature Science Update
January 5, 2001

Exploding meteors bombarding the Earth from space could be mistaken for
nuclear bomb tests, say seismologists of the Royal Netherlands
Meteorological Institute. This could present problems for monitoring the
Comprehensive Nuclear Test Ban Treaty (CTBT), which aims to halt the testing
of all nuclear weapons.

Laslo Evers and Hein Haak detected a sonic boom from a meteor explosion with
an instrument similar to those currently under construction for verification
of the CTBT.

The explosion released energy equivalent to 1.5 kilotons of TNT, the
researchers calculate. This is as big a bang as was made by several of the
US nuclear tests of the early 1960s, and at the lower end of the estimated
size of the Pakistani tests of 1998.

The future of the CTBT has been under a cloud since the US Senate decided
not to ratify it in 1999. But many other nations have already done so, and
plans are afoot for global detection systems that will alert the
international community to secret nuclear weapons tests.

Underground tests send out shock waves that seismic monitoring stations
designed for earthquake detection can pick up. And atmospheric tests create
a kind of low-frequency ('infrasound') sonic
boom which highly sensitive air-pressure meters (microbarometers) can
register. A worldwide network of 60 infrasound detectors is being built for
this purpose.

Situated near the village of Deelen in the Netherlands, the instrument Evers
and Haak used is not designated for CTBT verification -- it is primarily a
meteorological device. But in November 1999, it registered a most unusual
event.

At around four o'clock in the morning of the 8th November, a few early
risers in Germany and the Netherlands saw a flash in the dark sky above
northern Germany. A meteor -- a small chunk of space rock plunging through
the atmosphere -- had exploded at a height of about 20 kilometres.

The event was similar to a better-documented one that occurred in the middle
of the afternoon over New Zealand the previous July. On that occasion,
observers reported "a bright light, exactly like a flare", variously
described as blue, red, orange or yellow. It was followed by a loud boom,
and left behind a puff of brown smoke.

About one meteor detonates in the atmosphere every week. Most go unseen by
human eyes, as they break apart very high in the sky. Only rarely does one
strike or explode close to the planet's surface, such as the object that
levelled trees over hundreds of square kilometres in Tunguska, Siberia, in
1908.

That event aside, the height of these explosions usually hides their
tremendous ferocity. The explosion of November 1999 showed up on the Deelen
microbarometer as an infrasound blip slightly greater than the background
noise generated by ocean waves, which create a constant barrage of small
atmospheric booms called microbaroms.

Reported in the journal Geophysical Research Letters [1], Evers and Haak's
research highlights how crucial it will be for an infrasound network to be
able to distinguish between meteor explosions and genuine nuclear blasts.

[1] Evers, L. G. & Haak, H. W. Listening to sounds from an exploding meteor
and oceanic waves. Geophysical Research Letters 28, 41-44 (2001).
Received on Fri 05 Jan 2001 11:34:12 AM PST