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Chelyabinsk meteor had violent history before striking Earth

SpaceMeteorological Disasters
The meteor that exploded over Russia began its collision course toward Earth within the last 10 million years
Ribbons of jadeite in Chelyabinsk meteorites are signature of the asteroid's violent past, scientists say
The jadeite mineral in the Chelyabinsk space rock was forged at temperatures of up 2,000 degrees Celsius

Long before the Chelyabinsk asteroid slammed into the atmosphere over Russia last year, it struck another space rock in a high-intensity mash-up that put it on a collision course with Earth, scientists say.

A research team from Japan and Russia analyzed fragments of the Chelyabinsk meteorite to glean details about its history. They focused on places in the fragments that contained jadeite, a mineral that forms under high pressure.

The jadeite was found in ribbons of mineral called shock-melt veins. These veins are the result of melting that results from high-temperature, high-pressure situations -- such as asteroid-asteroid collisions. The veins ranged in width from roughly the thickness of a human hair all the way up to about 1 millimeter.

This particular jadeite had some telltale shapes, the team wrote Thursday in the journal Scientific Reports. Some of it was “needle-like,” the researchers found, like frost on glass. Other samples were “skeletal-rhombic,” a pattern that resembles a soccer ball except with diamonds instead of pentagons. Both of these shapes suggest the jadeite crystallized rapidly at a pressure of at least 3 to 12 gigapascals. (A gigapascal is 1 billion pascals; the atmospheric pressure on Earth is 101,325 pascals.)

If that pressure estimate is correct, then the temperature of the minerals as they formed the shock-melt veins would have been at least  1,700 to 2,000 degrees Celsius. Considering that the widest section of the vein was 1 mm, the jadeite likely solidified in just 70 milliseconds.

All of that led the researchers to calculate that an asteroid about 150 to 190 meters wide slammed into the rock that became the Chelyabinsk meteorite, at a relative speed of between 890 to 3,350 miles per hour. The collision probably took place in the last 10 million years, they added -- and it was the one that put the 56-foot-wide rock on a course to land in Russia on Feb. 15, 2013.

When the meteorite hit Earth’s stratosphere, it blew up with the force of a modern nuclear bomb. It was "the second largest asteroid airburst in our recorded history," the researchers wrote.

Previous studies have determined that the future Chelyabinsk asteroid experienced its first huge collision nearly 4.5 billion years ago,  followed by another around 290 million years ago.

Understanding the asteroid’s history could help earthlings prepare for future encounters with giant space rocks, the researchers wrote.

Copyright © 2014, Los Angeles Times
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