A bright flash of light. Moments pass. Then a rumble. The ground shakes a little. It can be only one thing — thunder and lightning. Right? That’s what most residents of Eastern Michigan thought when they heard a boom just after 8 p.m. on January 16.
The only problem? It was below freezing and there was hardly a cloud in the sky. That’s not the expected environment for a thunderstorm.
Social media lit up as confused natives reported a bright blue explosion followed by ground tremors. About two hours later, the National Weather Service in Detroit announced it could “confirm the flash and boom was NOT thunder.” The most likely culprit was a meteor.
Paul Gross is a meteorologist at WDIV-TV in Detroit. It’s been one of his goals to make TV meteorologists a resource for more than just covering the weather. And when “a giant meteor lit up the skies over the Detroit metropolitan area,” he says, it provided him an opportunity to do just that.
“The estimated 6-foot- [1.8-meter-] diameter space rock created a bright fireball that broke up,” he tells Science News for Students. This was due to the intense pressure, he says, “experienced as it raced through our atmosphere.” The meteor travelled at an estimated 45,000 kilometers (28,000 miles) per hour, creating a sonic “boom” that startled many people. That sound shook the ground enough, Gross says, to mimic a magnitude 2.0 earthquake.
The racing meteor’s aerial “flash was so bright that it was detected by the Geostationary Lightning Mapper,” he notes. That’s an instrument on the latest weather satellite — the National Oceanic and Atmospheric Administration’s GOES-16. Friction during the meteor’s flight through the atmosphere caused the space rock to break into pieces. Many of them, Gross notes, were large enough to be detected by the National Weather Service’s Detroit-area Doppler radar.
“Meteorite hunters immediately began searching the area where the radar showed the debris trail,” he says. And several space rocks turned up, he adds, “including one [found] by a cameraman at my television station.”
Story continues below video.
Not just a Michigan event
Someone didn’t have to live in Michigan to witness these all-natural fireworks. The American Meteor Society logged 355 separate reports of a brilliant fireball streaking across the heavens. They came in from seven states. The society pored over the reported observations. It also analyzed video footage and interviewed witnesses about the booms.
Using the visible reports, scientists were able to stitch together the path these falling space rocks likely took. They concluded these must have crashed down somewhere along a line from Brighten to Howell, Mich. That’s only 50 kilometers (30 miles) northwest of Detroit.
The reason people could witness the meteor’s flight was the incredible amount of light the rock produces as it raced through the atmosphere at 11.26 kilometers (7 miles) a second. Friction against the surrounding air slowed it down, converting its energy of motion (kinetic energy) to heat energy (thermal energy) and eventually to light.
This heating becomes so intense that the rock actually begins to burn up.
Most meteors, including this one, are chondrites. They are made of tiny chondrules, mineral bits containing silicon. Meteors also have a lot of iron, nickel and magnesium. The latter is the reason they appear to glow blue. Magnesium burns white, but only the blue rays penetrate to the ground.
If a meteor doesn’t totally burn up, parts of it can hit the ground. These remains are known as meteorites. But most meteors explode under the extreme heat of friction as they brush again air molecules in the atmosphere. Such an exploding space rock is known as a bolide. When a meteor transforms into a bolide, bits of the initial rock may now rain down over the surrounding countryside.
That’s where knowing about the sound becomes useful. The International Meteor Organization notes that “bangs or swishing sounds, or possibly other noises” can be linked with meteors and offer clues to whether they have shattered.
Those sounds may arrive several minutes after sighting the burning space rock. The reason? Sound travels much more slowly than light. Last week’s incoming meteor, for instance, traveled at Mach-37, according to NASA. That’s 37 times the speed of sound. That’s very fast. But the speed of light is 874,030 times the speed of sound.
On rare occasions, it’s possible to hear sound at the same time you see the meteor high in the sky. This may seem crazy, but it has to do with radio waves. Scientists have speculated that rapidly moving meteors may emit very-low-frequency (VLF) radio waves. VLF waves move at the speed of light and then interact with conducting bodies at the surface. These conducting bodies can be any structures or even the ground itself — anything that permits miniscule electrical currents to pass through. Sometimes this produces a shrill chirping sound….
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