William B. Cook, a NASA meteor expert, reported in a email to NASA headquarters that the fireball originated about 60 miles above West Bend, Wis., moving about 38,000 miles an hour toward the northeast before disintegrating about 21 miles above Lake Michigan.
As the meteor fell apart, it emitted low-frequency sounds that were recorded in the Canadian province of Manitoba, about 600 miles away. The blast released energy that was equal to at least 10 tons of TNT, Dr. Cook said, suggesting that the object that entered the atmosphere was at least 600 pounds and two feet in diameter.
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