Scientists for the first time were able to predict the arrival of an asteroid before it entered Earth's atmosphere.
The asteroid, estimated at 6 to 15 feet in diameter, entered the atmosphere over Sudan on Tuesday morning, providing a brilliant light show in East Africa as it burned up. Scientists said it posed no threat to people on the ground, though some tiny pieces of the object may have reached the Earth's surface.
The important thing, scientists said, was not the discovery of the object but the prediction of its trajectory.
It was first spotted Monday morning by the Catalina Sky Survey telescope near Tucson. At the time, the object was outside the moon's orbit. Data from the observation were relayed to the Near-Earth Object Program Office at the Jet Propulsion Laboratory in La Canada Flintridge.
"We did an impact analysis and saw that it would indeed hit" the Earth, or at least its upper atmosphere, said Don Yeomans, manager of the office, which monitors space rubble. He alerted space observers around the world, including the U.S. Defense Department.
Although advance notice of less than a day would hardly be enough time to prepare for the arrival of the kind of asteroid believed to have wiped out the dinosaurs 65 million years ago, Yeomans said the successful prediction "shows the system is working."
One reason the object wasn't spotted earlier, according to Yeomans, is that it was "at the lower end of what we can discover."
An object large enough to do serious damage to Earth and its creatures would presumably be seen much earlier.