Scientists see asteroid hurtle to Earth 
March 26, 2009 - 9:09AM 

Stunned astronomers watched a car-sized asteroid explode into a brilliant 
meteor shower as it crashed into Earth's atmosphere, then wandered into a 
Sudanese desert to pick up the pieces, a study reports.

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 on Wednesday.

"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 Centre in 
Cambridge, Massachusetts.

It was a routine logging, one of hundreds. But the computer system mysteriously 
refused additional data, recalled the Centre'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 per cent 
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 

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 1,400km 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 kilograms.

2008 TC3 falls into a category of very rare meteorites - accounting for less 
than one per cent 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 recognise ureilite asteroids still in space, he noted.

© 2009 AFP

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