Los Alamos National Laboratory
October 10, 1997
The object -- presumably a large, bright meteor known as a bolide -- was seen in the skies Thursday at about 12:47 p.m. Witnesses said the object was at least as bright as the full moon or as bright as the setting sun.
"The meteor made a huge sonic signal," said Doug ReVelle, a meteorologist in Los Alamos' Atmospheric and Climate Sciences Group. "They heard it like a freight train in El Paso."
Using data from Los Alamos listening stations originally set up to monitor nuclear explosions, ReVelle and other researchers in Los Alamos' Atmospheric and Climate Sciences Group analyzed the infrasonic signature created when the meteor entered the atmosphere.
When a meteor enters the atmosphere -- or when a large explosion is detonated -- it creates a sound or pressure wave that is below the range of human hearing. This infrasonic wave travels through the atmosphere and can be detected by special microphones that are set up in an array. By looking at the time of arrival of the sounds at different stations and the frequency of the infrasonic boom, researchers can pinpoint the location of the source and the determine the amount of energy that created it.
"The data from our array puts the meteor 441 kilometers due south of Los Alamos," said ReVelle. "We'll be looking for it in a location we've identified near El Paso."
ReVelle will join researchers from Canada, the University of New Mexico and Sandia National Laboratory on a search this weekend for any meteor fragments that may have reached the ground.
"The object's infrasonic signature was equivalent to the explosive yield of about 500 tons of TNT," ReVelle said. "That means the object was somewhere around one half to three-quarters of a meter in diameter."
Thanks to the infrasound array at Los Alamos, researchers at the Laboratory were able to narrow down the location where it may have landed pretty well.
In addition to searching for remains of the meteor -- which may have exploded into tiny bits in the sky -- the researchers will interview witnesses about the object: how bright it was; what it sounded like.
The object created a brilliant light as it streaked toward Earth. Witnesses in Santa Fe, Los Alamos, Albuquerque, El Paso and points in between saw the object in the sky.
ReVelle and the others will search all weekend for the object and collect other data as well.
"It could take weeks to find, but it could take a day or less, depending on how lucky we get," ReVelle said.
Infrasonic waves are very low frequency sounds that exist somewhere in the realm between hearing and meteorology, ReVelle said. The sounds are well below the range of human hearing, which ends at about 30 hertz, but actually can be detected as small changes in atmospheric pressure. If someone had a barometer that was sensitive enough, that person would be able to see fluctuations of several microbars when infrasonic waves arrive.
During the 1960s and early 1970s, before the rise of the satellite era, the United States Air Force operated a network of stations to listen for nuclear weapons tests. The listening stations were the nation's first line of detection for nuclear explosions worldwide.
The four arrays of listening stations operated by Los Alamos are the only infrasonic network left in full-time operation in the world. They can detect meteors that are as small as a few centimeters in diameter. The stations are useful because they can help validate other non-proliferation and verification techniques, and they cost very little to operate and maintain.
The Los Alamos stations, around since 1983, still are enlisted in the nation's nuclear non-proliferation efforts, but have provided a way for scientists to detect bolides, larger-than-average space debris that slams into Earth's atmosphere and creates brilliant fireballs in the sky.
Each year a number of large meteors enter the atmosphere and are detected by the Los Alamos array. Some meteors are tens of meters in diameter. ReVelle said each year about 10 meteors that are two meters in diameter -- with an energy equivalent of a one-kiloton blast -- enter the atmosphere. Most burn up or explode in brilliant flashes. Some hit the ground.
For this weekend's search, ReVelle will join Peter Brown of the University of Western Ontario; Alan Hildebrand from the National Research Council in Ottawa, Ontario; a researcher from University of New Mexico's Institute of Meteoritics; and Mark Boslough of Sandia National Laboratory.
Los Alamos National Laboratory is operated by the University of California for the U.S. Department of Energy.