A meteorite four centimetres in diameter, one of 47 recovered in the Nubian Desert of northern Sudan, remnants of asteroid 2008 TC3. (Nature/P. Jenniskens)

Scientists for the first time have recovered meteorite pieces from an asteroid first observed in space — a stroke of luck that could prove valuable when tracking space rocks heading on a collision course toward Earth.

The asteroid, called 2008 TC3, was first observed on Oct. 6 by astronomers in Arizona and was subsequently tracked as it entered the atmosphere and became a shooting star, the first time astronomers have managed that feat.

The space rock broke up in the atmosphere about 35 to 40 km above Sudan, giving astronomers little hope that they might recover fragments.

But SETI Institute astronomer Peter Jenniskens worked with colleagues at the University of Khartoum in the Sudan and, in December, they made an expedition to the Nubian Desert in northern Sudan.

Desert treasure trove

A flat, open and dry region with little vegetation, the desert turned up a treasure trove of pieces: 47 fragments with a total mass of 3.95 kg.

The findings were reported in this week's issue of the journal Nature.

For astronomers who have long clamoured for funding to send a robot probe to an asteroid to analyze the material, the finding was like a gift from the heavens, said University of Western Ontario astronomer Peter Brown, one of the authors of the report.

Being able to match lab analysis of meteorite composition to the data from asteroids — mostly in the form of light reflected from the space rocks — represents the "Holy Grail" for asteroid researchers, said Brown.

"This is really the first end-to-end sample recovery," he said. "This allows us to extend the concept of large-scale interplanetary prospecting."

The recovered meteorites were part of a group called ureilites, known for their dark colouring and porous structure and for containing microscopic nano-diamonds, while the asteroid seen in space was an F-class asteroid, defined for its dark and reflectionless surface.

Brown said the combined data from the asteroid observation and recovery of fragments means scientists can for the first time describe the material of F-class asteroids.

Astronomers believe asteroids are the remnants of material from the early days of the solar system, fragments that were never able to collide and merge to form into planets because of the disruptive influence of gravity from giant planets like Jupiter.

As a result, they are like a time capsule from the early days of the solar system, making them of intense interest to astronomers.

Tracking asteroids is also a priority for astronomers because of the potential threat of collision with Earth, although because of their fragility, F-class asteroids are more likely to break up in the atmosphere than hit the Earth.

The Canadian Space Agency is planning to launch a satellite in 2010 called the Near Earth Object Surveillance Satellite, or NEOSSat, capable of spotting asteroids whose path lies within Earth's orbit of the sun, which Brown says will aid in the tracking of future asteroids.

But even with more sophisticated methods, he says the odds of being able to track an asteroid, see it enter the atmosphere and recover the fragments is likely to be a rare trifecta.

"I think it will take another decade before we get another chance like this," he said. "This was an unusual event."