Space Rock Hunters Find Largest Chunk Yet of Exploded Wisconsin Meteor

The largest chunk yet of a meteor that exploded over Wisconsin last month has been found by intrepid space rock hunters. But the remnant, which broke into three pieces after hitting the ground, is still small enough to fit in the palm of your hand.

Marvin Killgore, the curator of meteorites for the Lunar and Planetary Laboratory at the University of Arizona, and his wife, Kitty, arrived in Mineral Point, Wisc., just days after the April 14 fireball sighting, and now have a 10.6-ounce (300-gram) chunk of space rock that may be the largest piece of the meteor found so far.

On April 14, people in southwestern Wisconsin and northern Iowa bore witness to a sonic boom and fireball that briefly lit up the late evening sky. The object, an ancient rock from space, entered the Earth's atmosphere as a ball of flames after a 4.5 billion year journey through the solar system.

NASA officials estimated that the meteorite, which measured about 3.3 feet (1 meter) across, exploded with a force equivalent to 20 tons of TNT.  

Meteorite hunters from around the world quickly flocked to the Wisconsin farm community that has become ground zero for the meteor fall to try to get their hands on a piece of the debris. A farmer discovered the first fireball fragment the morning after it exploded.

The Killgores found their fragment on a road near a local candle factory. The rock was split into three pieces on impact, and was even marked by the gravel road where it landed.

The Killgores' space rock is a breccia – a conglomeration of rock fragments cemented together. It most likely originated in the asteroid belt that orbits the sun between Mars and Jupiter.

"This one is relatively pristine, handled by very few human hands," Killgore said. "And it hasn't been on Earth all that long. It's exciting to be the first one to see something like this, to pick it up and hold it in your hand, and to know that it just came from somewhere away from here. It's pretty awesome."

There are likely other larger fragments of the Wisconsin meteor still out there that will be found in the coming years, Killgore said, but these pieces will also be more weathered.

The Killgores work with Marc Fries, a scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., to locate meteorite fragments. Using Doppler weather radar maps, they can triangulate the trajectory of objects that make it through Earth's atmosphere and reach the ground.

Since exploding meteors create clouds of debris (similar to atmospheric clouds) that are picked up by radar sensors, the area where pieces of the meteorite land can be detected using these meteorological devices.   

"The pieces can fall anywhere," Killgore said. "It's basically like tossing a handful of gravel into the grass and then see if you can find them."

The meteorite-hunting duo has already amassed one of the largest collections of meteorites in the world, with their heftiest find weighing a staggering 1,600 pounds (726 kg).

A different sample from the meteorite had been previously found by a local farmer, who sent it to the University of Wisconsin for examination. It was found to contain traces of magnesium, iron and silica compounds, in addition to other common minerals such as iron-nickel metal and iron sulfide.

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