Astronomers catch a shooting star for first time

By Seth Borenstein

updated 3:11 p.m. ET March 25, 2009

WASHINGTON - For the first time U.S. scientists matched a meteorite found on Earth with a specific asteroid that became a fireball plunging through the sky. It gives them a glimpse into the past when planets formed and an idea how to avoid a future asteroid Armageddon.

Last October, astronomers tracked a small non-threatening asteroid heading toward Earth before it became a "shooting star," something they had not done before. It blew up in the sky and scientists thought there would be no space rocks left to examine.

But a painstaking search by dozens of students through the remote Sudan desert came up with 8.7 pounds (4 kilograms) of black jagged rocks, leftovers from the asteroid 2008 TC3. And those dark rocks were full of surprises and minuscule diamonds, according to a study published Thursday in the journal Nature.

"This was a meteorite that was not in our collection, a completely new material," said study lead author Peter Jenniskens of NASA's Ames Research Center in California. For years, astronomers have been lobbying to send a robot probe to an asteroid, grab a chunk of it and return it to Earth for labs to analyze the material. Instead a piece of an asteroid dropped in their laps and the researchers were able to track where it came from and where it landed.

The asteroid, which mostly burned in the atmosphere 23 miles (37 kilometers) above the ground, is likely a leftover from when chunks of rock tried and failed to become a planet, about 4.5 billion years ago, scientists said.

"This is a look back in time and it came to us," said University of Maryland astronomer Lucy McFadden. She wasn't part of the study, but like four other outside experts praised the findings as important to the understanding of the solar system.

INTERACTIVE Below the belt Learn about close encounters of the asteroid kind

"It's a beautiful example of looking at an earlier stage of planet development that was arrested, halted," said NASA cosmic mineralogist Michael Zolensky, a co-author of the study.

But it also serves as a lesson for the future if this asteroid's big brother comes hurtling toward Earth.

Blowing it up like in the Bruce Willis movie "Armageddon" would not be smart because this type of asteroid turns out to be very much like a "traveling sandpile," Zolensky said. "If you blow it up, all the pieces are heading toward Earth."

Instead, a spaceship-aided nudge would be more effective, said NASA Ames Research Center director Simon "Pete" Worden, another study co-author. He is a longtime advocate of a worldwide program to plan for the threat of asteroids and comets hitting Earth.

"The real important issue is to understand the physics of these objects," Worden said.

There are many different types of asteroids, all classified from afar based on color and light wavelengths. This type is called class F and turns out to be mostly porous and fragile. University of Maryland's McFadden said it is unlikely that a class F asteroid could be any danger to Earth, even if it's bigger, because of its porous makeup which would cause it to break up before hitting.

It was full of metals, such as iron and nickel, and organics such as graphites, Zolensky said. And most interesting is that it has "nanodiamonds." These diamonds are formed by collisions in space and high pressure and they are all over the rocks, making them glitter like geodes, he said. But they are not big.

"If bacteria had engagement rings, these would be the right size for them," Zolensky said.

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