[b]Scientists see asteroid hurtle to Earth[/b]
PARIS (AFP) Stunned astronomers watched a car-sized asteroid explode into a brilliant meteor shower as it crashed into Earth's atmosphere, and then wandered into a Sudan desert to pick up the pieces, a study released Wednesday reported.
It was the first time ever that scientists recovered fragments from an asteroid detected in space, according to the study, published in the British journal Nature.
"Any number of meteorites have been observed as fireballs and smoking meteor trails as they come through the atmosphere," said co-author Douglas Rumble, a researcher at the Carnegie Institution.
"But to actually see this object before it gets to the Earth's atmosphere and then follow it in -- that's the unique thing."
The drama unfolded like an overheated Hollywood script, according to a reconstruction of the event by Nature.
On October 6 last year, an amateur star gazer in Arizona submitted the coordinates of an asteroid he had spotted to the Minor Planet Center in Cambridge, Massachusetts.
It was a routine logging, one of hundreds. But the computer system mysteriously refused additional data, recalled the Center's director, Tim Spahr.
"As soon as I looked at it and did an orbit manually, it was clear it was going to hit Earth," he told the journal.
The size and brightness of the asteroid -- which, by this time, has been assigned the name 2008 TC3 -- did not suggest danger, but Spahr followed standard safety procedure and called a NASA hotline.
He also alerted the Jet Propulsion Laboratory's Steve Chesley, who did a rush calculation on the asteroid's orbit. The program indicated a 100 percent chance of impact.
"I'd never seen that before in my life," he said.
The program also showed that the hurtling mass of rock would hit Earth's atmosphere -- with the force of one or two kilotonnes of TNT -- in less than 13 hours.
Suddenly, scientists accustomed to thinking in light years found themselves scrambling in real time to track the asteroid and figure out where its fragments might land.
Their chatter burned up the Internet and international phone lines. "IMPACT TONIGHT!!!", wrote physicist Mark Boslough of Sandia National Laboratories in New Mexico to colleagues, Nature reported.
Within minutes, it was determined that the asteroid would burst into pieces over the sparsely populated Nubian Desert in northern Sudan.
Tipped off by a meteorologist, a KLM passenger jet pilot flying from Johannesburg to Amsterdam spotted a brilliant flash some 1,400 kilometres distant as 2008 TC3 smashed into the atmosphere at 12,000 metres per second.
Weeks later, Peter Jenniskens, an astronomer at the SETI Institute in Mountain View, California and the study's lead author, was still waiting for the first report of a 2008 TC3 meteorite find. Nothing came.
So Jenniskens flew to Sudan in early December and teamed up with Muawia Hamid Shaddad of Khartoum University.
Together with a small regiment of students, they headed into the desert, asking local inhabitants along the way if they had seen a ball of fire in the sky.
When they zeroed in on the likely crash zone, the researchers fanned out to comb the area. In three days, they recovered 280 fragments weighing a total of several kilogrammes.
2008 TC3 falls into a category of very rare meteorites -- accounting for less than one percent of objects that hit Earth -- called ureilites, all of which may have come from the same parent body, Rumble said.
Being able to match spectral measurements of 2008 TC3 taken before it disintegrated with chemical analyses of the rock fragments should make it easier to recognize ureilite asteroids still in space, he noted.