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By Greg Clark
Arizona Daily Wildcat
January 29, 1998

Meteor fragments could save the world


Chris Richards
Arizona Daily Wildcat

Shards of the Gold Basin meteorite, which exploded over Arizona roughly 20,000 years ago, are on display in the UA Mineral Museum in the basement of Flandrau Science Center.

Retired UA engineering Professor James Kreigh was scanning for gold in the scrub desert of northwest Arizona two years ago when he picked up a small brown rock that made his metal detector squeak and squeal.

Curious, he dropped it in his pocket and continued hunting for gold.

His friends had cast away similar stones, obviously not precious metal, but Kreigh saved the few he found, thinking they might be meteorites.

Kreigh took the rocks to David Kring, a University of Arizona meteorite specialist, who told him one of the rocks was, indeed, a chunk of space debris.

Since then, Kreigh and his friends, John Blennert and Ingrid Monrad, have found more than 2,000 meteorite fragments spread over a 50-square-mile area.

The fragments are the remains of a single meteor that exploded when it barreled through Earth's atmosphere about 20,000 years ago, said Kring, a senior researcher at the UA's Lunar and Planetary Lab.

The age of the fragments was determined by chemical analysis that measured the amount of time the Earth's atmosphere has shielded the rocks from the high energy cosmic rays of space.

Timothy Jull, a research physicist at UA's Accelerator Mass Spectrometer Lab who analyzed the fragments from the Gold Basin field, found that the chemically-identical fragments fell to Earth between 20,000 and 25,000 years ago.

Until recently, the group members kept their findings secret while they carefully mapped and catalogued the location of every piece of space rock that turned up.

"It is just like an archaeological site," Kring said. "If it gets disturbed by too many collectors out there digging around, it could compromise the scientific integrity of the site."

What scientists may learn from a detailed survey of the site, Kring said, could prove useful if humans ever identify a large asteroid careening on a collision course toward Earth.

Meteors are asteroids that fall into the Earth's atmosphere, and very little is known about how strong these space-wandering rocks are, he said.

By studying the size and distribution of the meteorite fragments at the Gold Basin site, scientists can determine how the Gold Basin meteor exploded and how high above the Earth it was when it blew up.

This, in turn, will yield clues about the strength of asteroids, which will prove critical to calculations about the best way to push an asteroid out of a collision course with Earth, should that action ever be ever be necessary.

"We don't understand the strength of asteroids at all," Kring said. "So, in general, it is difficult to assess the hazards posed by an asteroid heading on an impact-course with Earth."

Some techniques scientists could use to alter an asteroid's course would actually shatter it rather than send it away from the planet, Kring said, which could be disastrous.

Knowing an asteroid's strength would allow scientists to use appropriate techniques to reduce its threat to Earth.

Such techniques could involve destroying the asteroid with a nuclear device, or heating one side, creating a gaseous jet that would propel it off course, Kring said.

"If it's very far away, a very slight change in direction or velocity would be enough to send it off course," he said.

As for the Gold Basin survey, Kring said it may continue for several years because the group has yet to find the meteorite field's outer boundary. He worries that its recent publicity may entice meteorite enthusiasts to search for the site.

Mike Farmer, UA Latin American studies senior and meteorite collector, predicted that most collectors will respect the ongoing scientific work and leave the site undisturbed.

"That is one of the most common types of meteorite. It may only be worth $2 to $3 per gram," said Farmer, who recently started meteorite dealing from his Internet Web site. "The scientific information is worth more than the meteorite at this point."

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