P. Brown/University of Western Ontario

Caught. An ultra-low-frequency sound detector recorded the signal (tall line between 400 and 500 seconds) of the asteroid blasting through the atmosphere.

Asteroid Watchers Score a Hit

Dick writes about Earth and planetary science for Science magazine.

Two days ago, Science reported that astronomers were predicting an asteroid impact for the first time (ScienceNOW, 6 October). Chalk one up for the astronomers. "The prediction clearly was correct," says planetary scientist David Morrison of NASA's Ames Research Center in Mountain View, California.

First detected on 5 October at the University of Arizona's Mt. Lemmon Observatory, the asteroid was calculated to enter the atmosphere over Sudan early on the morning of 7 October, erupting into a fireball in the sky but not damaging the ground. Although no sightings of the 2- to 3-meter-diameter rock burning itself up have come in from the ground, two other sorts of detections--one human and one instrumental--were made. Aviation meteorologist Jacob Kuiper of the National Weather Service in the Netherlands alerted KLM airliner pilots to the opportunity, and one flying 750 kilometers southwest of the predicted arrival spot reported a short flash just before the predicted time and in the predicted direction.

A ground instrument installed in Kenya to detect the extremely low-frequency sound waves of nuclear explosions recorded a signal generated 2 minutes before the prediction (see image), according to meteor specialist Peter Brown of the University of Western Ontario in London, Canada. To generate that signal, an extraterrestrial object would have needed to arrive from the predicted direction and with roughly the predicted energy, Brown calculates.

"I think we can be pleased with how this was handled on an international basis," says Morrison. Astronomers around the world were exchanging observations and impact predictions in near real time, he says, with NASA headquarters in the loop. He doesn't know whether anyone let the Sudanese know what was about to happen.

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