Scientists say that for the first time, they have tracked an asteroid as it crashed on Earth and recovered fragments of it in northern Sudan. The discovery will help researchers link meteorites to asteroids.
Astronomers often probe the night sky for new and interesting sights. But few expect to spot an asteroid heading toward the Earth. An astronomer in Arizona saw just that last October and quickly spread the word to other experts who used visual clues to ascertain the composition of the asteroid and other details.
NASA scientist Steve Chesley says astronomers had little time to study the object.
"It was coming in at about 6.5 kilometers per second when it crossed the lunar distance, just five hours after discovery," he said. "And 15 hours later, it actually hit the Earth, which is pretty fast compared to the Apollo mission when it took three days to get back from the moon."
As it entered the atmosphere, the asteroid turned into a fireball and broke apart, scattering debris over the remote desert region of northern Sudan.
NASA meteor expert Peter Jenniskens says scores of Sudanese watched the asteroid come down.
"It was a very frightening event," he said. "The big cloud of dust left behind in the atmosphere was photographed by people with their cell phones."
Jenniskens say it was a golden opportunity. He and other scientists quickly organized a team to try to recover fragments of the asteroid. With help from the University of Khartoum and several local students, they formed a search party.
Jenniskens says the group effort led to the recovery of some 280 small asteroid fragments.
"A lot of small ones were recovered, so I think the total mass is about five kilograms," he said. "So it's still a tiny fraction of the 80,000 kilograms that came into the atmosphere."
Experts have been studying meteorites for years to help understand the composition of planets and the origins of our solar system. But they say more information is needed to understand the link between meteorites found here on Earth and asteroids in space.
NASA mineralogist Michael Zolensky says this asteroid was unique because researchers can compare the data collected before it came down, with the recovered fragments.
"There are some mysterious processes that are happening to alter the asteroids' surface and making it hard to figure out what is going on," he said. "So here for the first time we have a complete evidence chain from an asteroid in space, whose color and optical spectra have been observed, all the way down to rocks that we can analyze in the lab."
Astronomer Lucy McFadden of the University of Maryland says the asteroid probably was a remnant of a small planet that formed millions of years ago. She says the discovery is a boon to researchers at NASA and elsewhere.
"No one at NASA headquarters had to decide its scientific merit," she said. "It landed right on our doorstep."
Already, scientists are studying the materials inside the fragments, which belong to a rare class of asteroids. They say the rocks contain iron, nickel and graphite, and are very porous, much like volcanic rock found here on Earth.