Consider the energy contained in a rock the size of a school bus. On a clear June morning, such an object, traveling at cosmic velocity, pierced the upper atmosphere over the empty expanse of the Mediterranean Sea, between Greece and Libya. It was not tracked. Its approach was masked by the glare of the sun. As it descended, friction heated it to incandescence, then to catastrophic failure. At an altitude of roughly 30 kilometers, it released its kinetic energy all at once in a silent, blinding flash.
The explosion was estimated at 26 kilotons of TNT, a yield slightly greater than the bomb dropped on Nagasaki. It occurred in the empty sky over empty water. There was no fireball seen from a city, no shockwave to shatter windows. The only witnesses were a few distant fishermen who might have seen a brief, strange flash on the horizon, and the sensors of a global network designed to listen for clandestine nuclear tests. The U.S. Department of Defense detected the infrasound signature. Seismic stations registered the faint tremor as the shockwave finally touched the sea's surface. The event was logged, analyzed, and filed away. It left no crater, no debris field easy to find. It was a reminder that the cosmos is an active shooting gallery, and that our planet is a moving target. A difference of a few hours in the rock's arrival time, and that titanic energy would have been unleashed not over desolate ocean, but over a densely populated continent. It was a major geological event that passed without a single human casualty, a testament to our profound luck and our profound vulnerability.