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(meteorobs) (Fwd) Private Meteorite Collectors, UA Scientists Team Up To D
Just thought you might be interested in this, slightly off topic but
interesting
Kim
------- Forwarded Message Follows -------
Date: Sun, 9 Aug 1998 5:38:08 GMT
From: Ron Baalke <BAALKE@kelvin.jpl.nasadot gov>
To: mplist@bitnik.com
Subject: Private Meteorite Collectors, UA Scientists Team Up To Discover History Of Portales Meteorite
Monday, Aug. 3, 1998
PRIVATE METEORITE COLLECTORS, UA SCIENTISTS TEAM UP TO DISCOVER HISTORY OF
PORTALES 1998 METEORITE
Contact: David A. Kring, 520-621-2024, kring@lpl.arizonadot edu
Thanks to private meteorite collectors, scientists with Lunar and Planetary
Laboratory (LPL) at The University of Arizona n Tucson have been able to
analyze, classify and curate pieces of a 143-pound meteorite that exploded
in the sky and strafed Portales, N.M., at around 7:30 a.m. on June 13.
The Meteorite Nomenclature Committee named the meteorite Portales Valley at
their meeting in Ireland last week and notified UA scientist David Kring
today (Monday). The committee is the international body of scientists who
review information on and approve the names and classifications of
meteorites.
"We could not possibly have done the work on the Portales Valley meteorite
without the assistance of private meteorite collectors," said Kring, a
geologist and senior research associate with LPL. The LPL has just published
Kring's updated guide for non- scientists, "Meteorites and Their
Properties," which includes tips on identifying and reporting meteorites.
Tucson meteorite collector Robert Haag provided samples of Portales Valley
for study, including a fragment the size of a large potato.
Michael G. Farmer, a UA student majoring in social and behavioral sciences,
donated one of the fragments he collected to the LPL. This is the piece
Kring analyzed.
Donations like Farmer's gift are pivotal, Kring said. Such donations are
necessary for compliance with international scientific protocol that says
when a meteorite is classified, a fraction of it must be curated at a
credible facility through perpetuity. This protocol gives scientists the
chance to independently study meteorite samples to check earlier analyses.
Future scientists with more powerful tools could also glean the specimen for
new information.
Skip Wilson, a well-known meteorite collector who lives in Portales, a town
in Roosevelt County renowned as one of the best meteorite collecting areas
in the world, has been a source of invaluable information, Kring added. A
fragment of Portales Valley fell within a half mile of Wilson's house.
"Skip said that he heard two booms followed by a series of pops, went
outside, and saw a smoky corkscrew trail in the sky. Because he heard a jet
passing overhead he thought an engine had fallen off of it," Kring said.
Wilson gathered a great deal of information from neighbors who also
witnessed the fall and reported it to Kring.
Other Portales residents likened the explosion to artillery shells. They
heard sonic booms. They felt tremors and saw vapor trails and dust trails.
One piece crashed through a barn. A school teacher saw a 37-pound fragment
blast a 10-inch deep crater in her driveway. For almost the next month,
residents recovered pieces of Portales Valley on road pavement, farm fields
and yards, Kring said. The biggest chunk weighs 38 pounds. All 38 meteorite
pieces so far found weigh a total 143 pounds. The consensus is that most of
the meteorite has been found.
Kring concludes from the material analyzed at LPL that Portales Valley is an
"H-type ordinary chondrite," but one that is a very unusual mixture of metal
and stony material.
Researchers at the University of New Mexico and the NASA Johnson Space
Center have also analyzed samples of the meteorite.
Chondrites are meteorites that contain chondrules, or millimeter-size
spheres of rock that once were molten droplets formed of dust directly from
the solar nebula -- the cloud of material that evolved into our solar system
about 4.6 billion years ago.
There are three groups of ordinary chondrites: LL, L and H. Scientists
believe that each group comes from a different small planet that once
orbited between Mars and Jupiter but was smashed to pieces by collisions.
The H (for high-iron) group contains the largest amount of the element iron
and the largest amount of iron metal of the three groups, Kring said.
The Portales Valley meteorite is striking because along with the typical
chondrules, it features unusually thick, bright, silvery shock veins. The
veins, which are several centimeters long or wide, or both long and wide,
are almost entirely metal. The amount of metal is so large that the
Meteorite Nomenclature Committee is waiting for additional analyses of the
metal before approving a final classification for the meteorite.
Given the evidence collected thus far, Kring suggests this history for the
meteorite:
* A flash-heating mechanism melted dust balls in the solar nebula, producing
molten droplets, like lava, which cooled and solidified to form the
millimeter-size cosmic marbles called chondrules. These chondrules and other
dust in the solar nebula accreted (stuck together) to form a planetesimal,
or small planet, that orbited between Mars and Jupiter. Researchers know
from earlier studies that the chondrules were produced in the solar nebula
about 4.6 billion years ago and that the planetesimal accreted about 10
million years.
* Temperatures in the planetesimal began to rise for two reasons. Impact
energies heated the small planet as it accreted. And once it had grown large
enough, heat generated within it by radioactive elements no longer radiated
into space. When temperatures within the small planet reached several
hundred degrees, rocks that had formed out of the solar nebula were
thermally altered. For example, most of the chondrules were destroyed; only
a few scattered relicts survived.
* At some point either the planetesimal, or perhaps an asteroid knocked from
it, collided with another asteroid. The shock from the collision briefly
melted some of the metal in the planetesimal and jetted veins of it through
the rock.
* After other possible collisions with asteroids, a small fragment of the
original planetesimal was ejected from the asteroid belt and into a new
orbit that eventually carried it to Earth.
* The meteorite struck Earth on June 13, hitting the atmosphere at more than
20,000 miles per hour. It was crushed by the increasing air pressure as fell
through the increasingly dense atmosphere. Then it blew apart into at least
38 pieces and scattered across a roughly 4-mile stretch at Portales.
Witnesses saw a smoke-like trail in the sky and heard a series of bangs that
sounded like artillery fire, a series of sonic booms and the explosion of
the meteoroid.
"As far as I know, only the people at the meteorite fall saw this, and that
is typical, Kring said. It illustrates why so few meteorites are found
although so many actually fall. Basically, if a meteorite does not fall
right next to you, you have very little idea that it has fallen."
The recent fireball over Casa Grande, Ariz., is a case in point. Hundreds of
people across the state witnessed the brilliant fireball at about 9 p.m. on
Sunday, June 7. Despite some methodical searches by Kring, the UA Meteorite
Recovery team and dedicated, experienced volunteer meteorite hunters, no
piece of this meteorite has yet been found. The Casa Grande fireball
apparently fell next to no one.
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