By Tom Henderson
Small Times Senior Writer
July 25, 2001 — The spectacular meteor that lit up the skies over the Eastern United States early Monday evening also lit up the phone lines at Los Alamos National Laboratory.
That’s where sensor arrays throughout the United States and Canada are monitored continuously
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| Rod Whitaker of Los Alamos National Laboratory examines one of the stations that is part of Los Alamos’ infrasound detection array. The long tentacles house the microphones that detect the ultralow frequency sound waves associated with the arrival of meteors. |
“We’re swamped — both with reporters and with government officials,” Douglas ReVelle, a scientist in the Earth and Environmental Sciences division of Los Alamos National Laboratory, said Tuesday.
“There’s a lot of interest in the government because of where it was at,” he said, referring to Washington, D.C.
Companies in the small tech industry, particularly those that make MEMS-based sensors, may be taking note, too. They will play a key role in the next generation of space- and ground-based monitors that will track future meteor collisions with Earth.
Though space-based sensors to monitor such explosive events use MEMS-based components, ground-based systems do not. However, that is about to change, ReVelle said, as costs and power consumption associated with MEMS systems go down.
“Until now, Earth-based sensors haven’t been really high tech. But there are new types of instruments on the market that are and we’ve been looking at them. Until now, it was hard to get the frequency range we needed in a really small size,” he said.
ReVelle said that MEMS-based and other forms of small tech sensors will soon be at the core of ground-based sensors. “We’ve been looking at them for a number of different reasons. They’re getting cheaper and cheaper to produce. They operate on lower power so they are cheaper to run and easier to charge.”
Monday’s light show was seen from Virginia to New York. The meteor was reported to have emitted a rainbow of colors, from bright yellow at its head to a rusty red at the end of its long-tapered tail. The sight was reportedly accompanied by a terrific burst of sound.
Experts said that the meteor was probably a small chunk of rock that scattered in the atmosphere. The only thing rare about it was that it revealed itself over a largely populated area.
PRESSURE WAVES ROLL CROSS-COUNTRY
Large meteors create low-frequency pressure waves when they enter the atmosphere.
ReVelle said that stratospheric conditions made it perfect for Earth-based low-frequency microbarometers around the United States to gather information on those waves. Many of the sensors are in the western United States, “and in the summer, the winds in the stratosphere travel east to west, unlike in the winter, when they travel west to east. They blow west to east like the lower winds in the winter.”
ReVelle said early indications were that the collision of the meteor with the Earth’s atmosphere was powerful enough to be detected by sensor arrays stationed as far away as Alaska and Hawaii. He said the sensors detect frequencies from just below the threshold of human hearing, which is in the 10-20 hertz range, all the way down to .01 hertz.
Ground-based sensors were first put into place in the early 1980s to monitor underground nuclear testing by the Chinese and Russians. Later, MEMS-based and other small tech sensors on board satellites have been used to gather corroborative information.
Los Alamos, which now runs sensor arrays at four sites in the western United States, installed its modern prototypes in 1997. Five other arrays run by universities range from north of New York City to Lac DuBonnet, Manitoba, to Hawaii.
While nuclear testing has at least temporarily stopped, meteor collisions have not. “We’ve recorded a lot of them, enough so that we can now make predictions on their frequency,” ReVelle said.
Scientists think that one of the biggest meteor explosions ever was the one that many believe wiped out the dinosaurs millions of years ago. The most famous meteor collision of modern times was near the Stony Tunguska River in a mosquito-filled swamp in Siberia. The meteor exploded above ground on June 30, 1908, leveling trees for miles around.
“That was a 10-megaton event,” ReVelle said. “A very, very major event. The biggest event ever recorded. We now expect a 10-megaton event about every 120 years, and it’s been 83, so . . . ”
A megaton equals the explosive energy of one million tons of TNT. The atomic bomb that leveled Hiroshima was rated, said ReVelle, at about 15 kilotons, or about 15,000 tons of TNT.
ReVelle said he expected Monday’s meteor to have roughly the explosive force of the two most recent big celestial collisions recorded by Los Alamos researchers — one of 2-3 kilotons last Aug. 25, and one of from 1-10 kilotons on April 23 of this year. Ground-based sensors rated it at one, with space-based sensors, which use more MEMS and small tech components, rating it at the higher end.
“Normally, the sensors are more in agreement. We’re still trying to figure out why they were so different this time.”
The first meteor plunged into the atmosphere several hundred miles west of Baja California in Mexico. The second one entered the atmosphere off the coast of Acapulco. Each could have been about 6 feet in diameter.
ReVelle said that while collisions of that nature are fairly rare, smaller but still significant explosions involving celestial objects colliding with Earth’s atmosphere happen regularly.
“We get about 50 events a year in the 10th of a kiloton range, and a couple of hundred a year all over the globe in the hundredth of a kiloton range.”
That’s hundreds of explosions in the atmosphere each year, each with the explosive force of at least 10 tons of TNT detonating.
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CONTACT THE AUTHOR:
Tom Henderson at [email protected] or call 734-994-1106, ext. 233.