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Asteroid affirms prediction program


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POSTED: Wednesday, October 08, 2008

Asteroids routinely hit the Earth's atmosphere but the impact by one over northern Africa Monday was the first time astronomers saw one coming and accurately predicted the time and place it would hit, a University of Hawaii astronomer said yesterday.

That successful prediction bodes well for a Maui-based system in development to warn against potentially hazardous space rocks, David Tholen said.

The impact occurred at 4:46 p.m. Hawaii time Monday over northern Sudan. A colleague compared the asteroid, called 2008 TC3, with the size of a Volkswagen, he said.

NASA's Jet Propulsion Laboratory in Pasadena, Calif., sent an e-mail saying the impact occurred yesterday at 2:46 a.m. universal time but provided no details, said Tholen, who hunts for hazardous near-Earth asteroids.

Tholen said more than 500 observations were made of the asteroid approaching Earth by astronomers all over the world, primarily in Europe and western Asia.

"It was the first opportunity to really test the whole impact-prediction software system on a real object," he said, adding that it was 100 percent accurate.

There was one report of a visual sighting by a KLM Airlines pilot, but it was far from the impact location and merely saw "a streak of light," he said.

The only other solid piece of data came from an infrasound station in Kenya that listens for very low-frequency sound waves and can detect the entry of fireballs, he said.

Asteroids create sonic booms, but a lot of the sound energy is lower in pitch than the human ear can hear, he said. The station detected sound waves at about the time the asteroid was predicted and within a few degrees of the impact location, he said.

The Mount Lemon telescope of the NASA-funded Catalina Sky Survey first observed the object early Monday. The Near Earth Object Observation program, called Spaceguard, plots the orbits of these objects to determine if any is a threat to Earth.

Calculations by the University of Pisa in Italy were reported to the International Astronomical Union's Minor Planet Center, located at the Harvard-Smithsonian Center for Astrophysics — the worldwide clearinghouse for asteroid and comet observations.

JPL and the University of Pisa have software for impact calculations, but some amateurs did their own calculations, which were "remarkably consistent" with professional groups, Tholen said.

Tholen said the episode "gives us a lot of confidence in the whole system of predicting when and where an asteroid impact would occur."

And when the Panoramic Survey Telescope and Rapid Response System under construction on Haleakala is up and running, "we should see more events like this," he said. Pan-STARRS' mission will be to detect potentially threatening asteroids and comets.

"These things happen every month or two and most of the time just go unnoticed, except people on the ground who see the fireball," Tholen said. "This time, astronomers saw it first and could predict the fireball. It was unique."