A spectacular fireball seen by hundreds of people from Iowa to Ontario delivered precious samples from the asteroid belt to the lake country of southern Michigan Tuesday night.
On January 16th around 8:10 p.m. EST, a brilliant, green fireball crackled across southern Michigan skies. Eyewitnesses described it as brighter than the full Moon with sparks and an orange tail. At least 77 observers reported hearing explosive sounds as the meteoroid broke apart overhead.
The American Meteor Society (AMS), a clearinghouse for meteor sightings, has received 657 reports of the fireball with some as far away as Iowa and southern Ontario.
The fireball traveled relatively slowly at around 45,000 km (28,000 miles) per hour. That sounds fast, but it's more than 4½ times slower than a typical summertime Perseid. Its slow speed and great brilliance suggests a fairly large space rock that penetrated deep into the atmosphere, according to Mike Hankey of the AMS.
While fireballs are relatively common, ones that drop meteorites are rare, and it's rarer still for someone to find those black treasures. But by using Doppler weather radar data and seismic traces (more on that in a moment), meteorite hunters were able to pinpoint the strewn field, the name for the ground footprint where the space rocks might have fallen. Lately of the asteroid belt, these interplanetary fragments now call the Township of Hamburg, Michigan, home.
The strewn field extends about 5 miles, oriented east-southeast to west-northwest, from about Highway 23 up to Bass Lake, some 20 miles northwest of Ann Arbor. Since the area has many lakes, make sure the ice is sound before venturing out.
Anyone living in that area should be on the lookout for black rocks poking out of the snow similar to what Ward is holding in the photograph above. The black coating, called fusion crust, forms when the outside of the meteoroid is heated and melted by friction from the air during its flight through the atmosphere. Fusion crust is typically only 1-2 mm thick.
The Michigan fireball not only put on a light show, it "knocked down the door," announcing its arrival with a 2.0-magnitude seismic event recorded by the U.S. Geological Survey. The blast was not from the impact itself but from the air pressure wave created during the explosive breakup of the meteoroid in the atmosphere.
A preliminary analysis indicates it's possibly an L6 chondrite, a common stony meteorite type. The "L" stands for low iron and "6" (on a scale from 3 to 7, from least to most altered by heat) indicates that the meteorite was strongly heated, so it likely originated from a larger asteroid. Samples are on their way now to the Chicago Field Museum for more detailed analysis.