[meteorite-list] Correction to article re: NEXRAD Doppler images of Wisconsin bolide

From: Matson, Robert D. <ROBERT.D.MATSON_at_meteoritecentral.com>
Date: Wed, 5 May 2010 17:03:05 -0700
Message-ID: <7C640E28081AEE4B952F008D1E913F17035CED5D_at_0461-its-exmb04.us.saic.com>

Hi All,

Sent this reply to the list last night, but it appears to have
disappeared
into cyberspace. Resending:

- - - - -

Marvin is mistaken about the first radar return being at only
30,000 feet (assuming the article has quoted him correctly).
The initial radar return was at 28.3 km (~93,000') +/- 3 km.

The "14-mile-long shower of fragments" is also an underestimate.
The actual distance, based on strong radar returns, is at least
30 miles.

Cheers,
Rob

-----Original Message-----
From: meteorite-list-bounces at meteoritecentral.com
[mailto:meteorite-list-bounces at meteoritecentral.com] On Behalf Of Ron
Baalke
Sent: Wednesday, May 05, 2010 4:06 PM
To: Meteorite Mailing List
Subject: [meteorite-list] Arizonans Find Largest Meteorite Fragment
FromSpectacular Midwestern Fall


http://uanews.org/node/31788

Arizonans Find Largest Meteorite Fragment From Spectacular Midwestern
Fall

By Jeff Harrison
University of Arizona
May 4, 2010

UA meteorite curator Marvin Killgore has a 300-gram piece of the object
that exploded over Wisconsin in April.

People in southwestern Wisconsin and northern Iowa on April 14 witnessed
a sonic boom and a fireball that briefly - and spectacularly - lit up
the late evening sky. It was the result of an ancient rock that ended
its 4.5 billion year journey through the solar system in a ball of
flames entering Earth's atmosphere.

NASA officials estimated that the rock, a meteoroid some 3.3 feet
across, blew apart with the force equivalent to 20 tons of TNT. Videos
of it are widely available on the Internet.

And it also set off what one meteorite hunter called "the ultimate
Easter egg hunt."

Marvin Killgore, the curator of meteorites for the Lunar and
<http://cos.arizona.edu/sci_departments/planetary_sciences.asp>
Planetary Laboratory at the University of Arizona, and his wife, Kitty,
were among the first of a phalanx of meteorite hunters from around the
world to arrive in Mineral Point, Wisc., just days after the sighting.

To date, the Killgores have what may be the largest fragment of the
meteorite, a pristine chunk of space rock weighing about 300 grams,
although Marvin Killgore said rumors of a larger meteorite are
circulating.

The Killgores work with NASA Jet Propulsion Laboratory scientist Marc
Fries on locating meteorites. They use Doppler weather radar sites on
the Internet to triangulate the trajectory of objects heading through
the atmosphere to the ground. Much like atmospheric clouds, exploding
meteoroids create clouds of debris that are picked up as radar
signatures and form a "strewn field,"
the zone that encompasses the area where pieces of the meteorite land.

This particular object was a breccia, a conglomerate of rocks embedded
in a fine-grained rock matrix. It most likely came from the asteroid
belt orbiting the Sun between Mars and Jupiter.

Killgore estimated the rock first detonated at 30 kilometers - about 18
miles above the Earth's surface - with the first radar signature
occurring at about 30,000 feet, sending a two-mile wide,14-mile-long
shower of fragments into the Wisconsin countryside.

The Killgores, along with their daughter and son-in-law, Laura and Nick
Center, drove straight through from Arizona to Wisconsin almost as soon
as they heard about it.

They were not alone. Marvin Killgore said there were about 100 other
meteorite hunters in Mineral Point the day they arrived, combing through
the freshly plowed fields, grass-lined fences and roadways for a prize.

Mineral Point, a farm community midway between Madison and Dubuque,
Iowa, had become Ground Zero for the meteorite fall.

"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."

Finding them generally involves a lot of walking.

"We have a metal detector, but there is so much metallic farm debris in
the fields from tractors and other equipment that we just use our eyes
and magnets," said Kitty Killgore. The magnets are attached to walking
sticks that aid in finding meteorites made of iron or are high in iron
content.

The Killgores found their meteorite on a road near a local candle
factory.
It had split into three pieces on impact, stamped with an impression
from the gravel on the road where it hit.

A sample from the meteorite found by a local farmer was sent to the
University of Wisconsin and found to contain traces of magnesium, iron
and silica compounds, as well as other common minerals like olivine and
pyroxene. It also contained iron-nickel metal and iron sulfide, minerals
typically found in primitive meteorites discovered on Earth.

Some meteorites are valuable enough to fetch several thousand dollars on
the market - part of the reason, Killgore said, why the number of
meteorite hunters has grown dramatically in recent years as technology
has made them easier to find.

Easier but with no guarantees. He said many people will spend one or two
thousand dollars and a couple of weeks at a site and come away
empty-handed.
A few will spend upwards of $50,000 at a potentially rich site with
hopes of recouping their expenses and making a profit.

Marvin and Kitty Killgore themselves have amassed one of the largest
collections of meteorites in the world, more than six tons. The largest
weighs nearly 1,600 pounds.

Selling a fraction of the collection could let them live comfortably.
Their goal instead is to keep the collection intact and in Arizona to be
used for scientific investigation. That will include some public
exhibits as well.

One is scheduled for June 12-13 at the Foothills Mall in Tucson. The
Wisconsin meteorite will be on display along with some major iron and
stony-iron pieces.

Marvin Killgore said there most likely are larger fragments from the
Wisconsin meteor than the one he found, and pieces of it will show up
for years to come. But over time those fragments will have weathered, he
said.

"This one is relatively pristine, handled by very few human hands," he
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."

Contact:

Marvin Killgore
UA Lunar and Planetary Laboratory
killgore at lpl.arizona.edu

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Received on Wed 05 May 2010 08:03:05 PM PDT