Using a system designed to detect
clandestine nuclear weapons tests, researchers at the Department of
Energy’s Los Alamos National Laboratory detected two large meteors that
recently entered the atmosphere above the Pacific Ocean.

Using Los Alamos listening stations that can help alert international
authorities to weapons tests by rogue groups or nations, Los Alamos
researchers Rod Whitaker, Doug ReVelle and Peter Brown detected two meteors
entering the atmosphere on April 23 of this year and on Aug. 25, 2000. Data
from orbiting space platforms confirmed the objects. The Los Alamos team
waited until the space-platform data were released publicly last week before
releasing their data.

The meteors were very large, measuring about six and ten feet in diameter.
They undoubtedly appeared as huge fireballs in the sky. Such large, fiery
meteors are called bolides.

When a bolide enters the atmosphere — or when a large explosion is
detonated — it creates a sound, or pressure wave, that at long-range is
below the levels of human hearing. This infrasonic wave travels through the
atmosphere and can be detected by special microphones that are set up in an
array. Los Alamos operates four arrays located throughout the United States.
By looking at the time of arrival of the sounds at different array stations
and at the frequency of the infrasonic signal, researchers can pinpoint the
location of the source and determine the amount of energy that created it.

The April 23 meteor plunged into the atmosphere above the Pacific Ocean
several hundred miles west of the northern Baja California region of Mexico.
The August 2000 meteor entered the atmosphere off the coast of Acapulco,

The pressure wave of a bolide entering the atmosphere is akin to a pressure
wave created by an explosion. Because of this, ReVelle and Whitaker often
speak of meteor size in terms of explosive yield — the larger the yield,
the greater the diameter of the meteor.

The August 2000 meteor had an explosive yield equivalent of 2,000 to 3,000
tons of TNT. The April meteor was much larger, with an equivalent explosive
yield of 6,000 to 8,000 or more tons of TNT. Based on the energy and speed,
ReVelle and Whitaker estimate the first meteor was six feet in diameter.
The second meteor probably was at least twice as large. “Had anyone seen
the April 23 event, they would have seen quite a show,” ReVelle said. “That
meteor was one of the five brightest meteors that have ever been recorded,
it was a very large bolide.”

Each year a number of large meteors enter the atmosphere and are detected
by the Los Alamos arrays.

ReVelle said that on the average, 10 or more meteors that are six feet
in diameter enter the atmosphere each year. Larger bolides entering the
atmosphere occur less frequently, but they do occur nevertheless.

Bolides produce their brilliant light shows tens of miles above Earth’s
surface. Fortunately for people on the ground, most meteors explode into
thousands of tiny pieces or burn up completely before they hit the surface.
If the August and April meteors made it to the surface, they probably hit
water — well away from any populated areas.

When they do hit the ground, their destructive power is unmistakable. The
remains of a very large bolide collision with Earth can be seen at Meteor
Crater, Ariz.

The Los Alamos infrasound arrays don’t provide advanced warning of a
meteor’s approach because the infrasonic signature takes several minutes
to hours to reach the stations. But the stations do have tremendous
potential for detecting clandestine nuclear weapons tests, and for
forecasting the rate of large bolide entry into the atmosphere.

The meteors of April and August played an important role in helping
non-proliferation technology efforts.

“Because those two events were detected by our four arrays and by five other
arrays operated by the International Monitoring System, we are able to use
the space platform data to calibrate our instruments, and analyses, to make
them better able to pinpoint the exact location where these events occurred,”
Whitaker said. “Every time we hear a bolide, we learn something about this
technology and are better able to fine tune it.”

But with other non-proliferation technologies available, why are infrasound
arrays necessary?

“Infrasound is very simple, inexpensive and easy to operate as a backup
system,” Whitaker said. “Infrasound arrays are listening twenty-four hours
a day, seven days a week. Sometimes other technologies miss events that
infrasound arrays detect. Consequently, infrasound is inexpensive insurance
for cost effective monitoring, and it is something that’s available to the
entire international community – which isn’t the case with some other

Los Alamos National Laboratory is operated by the University of California
for the U.S. Department of Energy’s National Nuclear Security Administration.