April 23, 2012 - On Sunday morning, April 22nd, just as the Lyrid meteor shower was dying down, a spectacular fireball exploded over California's Sierra Nevada mountain range. The loud explosion rattled homes from central California to Reno, Nevada, and beyond. According to Bill Cooke, head of NASA's Meteoroid Envronment Office, the source of the blast was a meteoroid about the size of a minivan.
"Elizabeth Silber at Western University has searched for infrasound signals from the explosion," says Cooke. "Infrasound is very low frequency sound which can travel great distances. There were strong signals at 2 stations, enabling a triangulation of the energy source at 37.6N, 120.5W. This is marked by a yellow flag in the map below."
"The energy is estimated at a whopping 3.8 kilotons of TNT, so this was a big event," he continues. "I am not saying there was a 3.8 kiloton explosion on the ground in California. I am saying that the meteor possessed this amount of energy before it broke apart in the atmosphere. [The map] shows the location of the atmospheric breakup, not impact with the ground."
"The fact that sonic booms were heard indicates that this meteor penetrated very low in atmosphere, which implies a speed less than 15 km/s (33,500 mph). Assuming this value for the speed, I get a mass for the meteor of around 70 metric tons. Hazarding a further guess at the density of 3 grams per cubic centimeter (solid rock), I calculate a size of about 3-4 meters, or about the size of a minivan."
"This meteor was probably not a Lyrid; without a trajectory, I cannot rule out a Lyrid origin, but I think it likely that it was a background or sporadic meteor."
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