Lucky break: Astronomers are excited about the meteor fragments, as they belong to a rare class of meteors.
SYDNEY: For the first time, astronomers discovered an asteroid hurtling toward Earth hours before it entered the atmosphere.
They watched the car-sized asteroid explode as it entered Earth's atmosphere and then collected its fragments from the Sudanese desert.
It was the first time an asteroid had been spotted before falling to Earth, making the 47 fragments they recovered an important link between telescope observations of asteroids and laboratory analyses of meteorites.
The recovery
"It's a unique opportunity to compare a meteor in hand with an asteroid in space," said Peter Jenniskens, an astronomer with the Search for Extraterrestrial Intelligence Institute (SETI) in California and the lead author of the paper, published today in Nature.
On October 6, 2008, the Catalina Sky Survey telescope in Arizona first spotted the asteroid, known as 2008 TC3. Astronomers around the world followed the Earth-bound asteroid, urgently plotting its trajectory to try to predict where it would crash down to Earth.
Nineteen hours later, 2008 TC3 entered the atmosphere and exploded 37 km above a desert in northern Sudan. Because the explosion occurred at such a high altitude, the asteroid was still moving very fast and its explosion was highly energetic.
Most of it turned to dust; however, a search of the area led by Jenniskens and Muawia Shaddad of the University of Khartoum in Sudan located 47 meteorite fragments.
Dodging debris
The smallest fragments are only a centimetre across, while the largest is the size of the palm of a hand, Jenniskens said. In total, researchers collected 3.95 kg of fragments.
Robert McNaught, an astronomer with the Australian National University in Canberra, said the events of 2008 TC3 show that astronomers can predict the precise impact point of asteroids with only a day's warning. This accuracy, he said, has "significant consequences for emergency management."
The recovered fragments have given researchers a unique opportunity to better understand the connection between asteroids and meteorites.
Double the data
Researchers can study asteroids in space by analysing the spectra of light they reflect, but this only provides general information about their chemical composition. They can also study meteorites recovered on Earth, but it is hard to discern information about their parent asteroid.
In the case of 2008 TC3, researchers can work with both types of observations, building a link between asteroid and meteorite data.
"This paper makes that link stronger, at least for one class of meteorites," said Charley Lineweaver, an astronomer with the Australian National University in Canberra.
Rare meteor
A large team of researchers has begun analysis on one 2008 TC3 fragment, finding it belongs to a rare class of meteorites called ureilites. Ureilites, Jenniskens said, appear to be halfway between primitive asteroids - those made up of material from the early solar system - and non-primitive asteroids. Primitive asteroids contain small molten glass globules; non-primitive asteroids were once completely molten.
Because ureilites are very fragile, this is the first time scientists have collected a meteor of this class. "It was a very unique meteor," Jenniskens said. He added that studies on the fragments were just beginning.
