A meteor streaked across Michigan skies on Tuesday night with a flash of bright light and a rumble that reportedly sounded like thunder. University of Michigan experts are available to discuss the event.
Larry Ruff, professor in the Department of Earth and Environmental Sciences, is a seismologist who oversees the Ann Arbor seismic station, which is on the U-M campus. He said the Ann Arbor seismograph recorded the event and that it produced a strong and unusual seismic signature.
"This was an explosion in the atmosphere, not an earthquake, and it produced a seismogram that is very different from what you get from a small, regional earthquake," he said. "Seismologists who are experienced enough can tell that it's not an earthquake because the character is very different."
Ruff has worked at the U-M seismic station since 1982 and said he has never seen such a strong signal recorded there following an atmospheric event.
"In some of the previous notable sonic booms and meteor explosions, I looked and never saw a signal like this," he said. "This one just stands out. This is the strongest signal—the best seismogram—of all the ones I've seen over the years at the Ann Arbor station."
Michael Liemohn, professor in the Department of Climate and Space Sciences and Engineering, is an expert on space hazards. He saw the meteor from his car and recognized it as a "bolide," a small meteor that explodes and burns up in the sky before reaching the ground. He can discuss space hazards in general, asteroid detection, and a relatively recent incident in Siberia in which the sonic boom from a bolide caused property damage and injuries.
"This was probably a rock of only a few feet in diameter," he said. "The primary way that a bolide can be dangerous is broken glass. Weird, but true. They are moving at thousands of miles per hour through the atmosphere, so, supersonic speeds, and they create a sonic boom that can reach the ground. If this bolide had been a slightly bigger rock, then it could have broken windows.
A bolide that exploded over Siberia a few years ago, which was a roughly 10-ton rock—about the size of the University of Michigan 'rock' at Hill and Washtenaw—sent roughly 1,000 people to the hospital, some with broken bones from falling over but most from broken glass as windows exploded inward.
"Dark-colored space rocks, aka asteroids, of this size are essentially invisible against the blackness of outer space. We can often detect the really big ones, house-sized or bigger, but boulder-sized are just too small to see until they are very close to Earth. Even then, we have to be looking in just the right direction. NASA's Planetary Defense Program is designed to identify and deflect larger rocks. If they predict that there is a good chance it might our planet, then NASA has several options to deflect the path of the asteroid, like hitting it with a missile or shooting it with lasers."
Ted Bergin, professor and chair of the Department of Astronomy, uses chemistry to probe the physics of star and planet formation and to trace the molecular origins of life.
"These rocks are the leftovers of planet formation—they never made it into a planet
like our own," he said. "Because of that, they contain inside them the history of our own origins and can tell us how a planet like our own was born.
"Meteorites fall from the sky every day. Most of them are so small they burn up in the upper atmosphere and don't reach the ground. However, in some cases they are large enough to penetrate deeper into the atmosphere where they either explode before hitting the ground or reach the ground itself. These bodies are on the order of meter-sized or larger. The frequency that they impact the atmosphere is in terms of one every 3 to 10 years. Recall that most of the Earth's surface is covered by water—so there is a greater chance of this hitting the ocean. So we have no particular worry or concern—but it does happen and can be spectacular."
David Gerdes, professor in the departments of Physics and Astronomy, studies the structure and evolution of the universe.
"The Earth is hit by meteors all the time—about 1,000 visible meteors reach the Earth's atmosphere every second. Most of these are no bigger than a grain of sand.
"Meteors that penetrate deep enough into our atmosphere to produce the large visible and audible burst like we experienced last night come from object with diameters of about one meter or more, and are more rare. Experts estimate that a 1-meter sized object hits us every few months, a 10-meter sized object (like the one that appeared over Russia in 2013, causing injuries and significant property damage) happen every few years to decades, and a 100-meter sized object every few thousand years.
"Last night's event was recorded by dashboard cameras, security cameras, lightning sensor, and seismological sensors from many locations. These data will help us form a much better picture of this object's size and trajectory, and if and where any fragments reached the Earth."