Updated

A fiery meteor created a thundering explosion and traced a rare daylight fireball seen for about 600 miles across Nevada and California, before apparently breaking up harmlessly at high altitude, astronomers said.

NASA researchers at the Jet Propulsion Laboratory said the midair explosion Sunday, centered over California's Central Valley just east of the San Francisco area, was the equivalent of the detonation of about 3.8 kilotons of TNT -- about one quarter the energy released by the atomic bomb dropped on Hiroshima, Japan, in 1945.

"The meteor was probably about the size of an SUV," said Donald Yeomans, manager of NASA's Near-Earth Object Program Office at the laboratory, which is in Pasadena, Calif. "This was a big one. An event of this size might happen about once a year, but most of them occur over the ocean or an uninhabited area."

[pullquote]

There were no reports Monday that any fragments of the object had reached the ground or caused any damage after it broke apart overhead. No major telescope in the region tracked the early-morning fireball.

NASA astronomers said the explosion might have been five to 10 miles high, which was high enough to allow the sound to spread widely.

Every day, countless meteors reach the Earth's atmosphere. Most are smaller than a grain of sand, according to the American Meteor Society, and usually burn up in the air and never hit the Earth's surface.

On rare occasions, the falling bits of space debris do hit now-populated areas. There is no record of anyone ever having been killed by a meteorite -- a meteor that slams into Earth -- but in recent years, there have been verified accounts of a meteorite hitting a bedroom in Alabama, a dining room in Connecticut and a parked car in Peekskill, N.Y.