Tiny meteorites found in the Sierra foothills of northern California were part of a giant fireball that exploded over the weekend with about one-third the explosive force of the atomic bomb dropped on Hiroshima in World War II, scientists said Wednesday. The rocks each weighed about 10 grams, or the weight of two nickels, said John T. Wasson, a longtime professor and expert in meteorites at UCLA's Institute of Geophysics and Planetary Physics. Experts say the flaming meteor, dating to the early formation of the solar system four billion to five billion years ago, was probably about the size of a minivan when it entered the Earth's atmosphere with a loud boom early Sunday. It was seen from Sacramento, California, to Las Vegas and parts of northern Nevada. An event of that size might happen once a year around the world, said Don Yeomans of NASA's Near-Earth Object Program Office at the Jet Propulsion Laboratory in Pasadena, California. “But most of them occur over the ocean or an uninhabited area, he said. “Getting to see one is something special,” he said. He added, “most meteors you see in the night's sky are the size of tiny stones or even grains of sand, and their trail lasts all of a second or two.” The meteor probably weighed about 154,300 pounds (70,000 kilograms), said Bill Cooke, a specialist in meteors at NASA's Marshall Space Flight Center in Huntsville, Alabama. At the time of disintegration, he said, it probably released energy equivalent to a 5-kiloton explosion — the Hiroshima bomb was 15 kilotons. “You don't often have kiloton rocks flying over your head,” he said. The boom, another expert said, was caused by the speed with which the space rock entered the atmosphere.
