[meteorite-list] SwRI Researchers Identify Asteroid Breakup Event In The Main Asteroid Belt

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:01:33 2004
Message-ID: <200206131538.IAA03109_at_zagami.jpl.nasa.gov>

http://www.swri.org/9what/releases/15asteroid.htm

SwRI researchers identify asteroid breakup event in the main asteroid belt
Southwest Research Institute
June 13, 2002

Boulder, Colorado -- A new study at Southwest Research
Institute (SwRI) has identified a recent asteroid breakup event in the
main asteroid belt. Computer simulations have shown that the event
occurred 5.8 million years ago, when a 15-mile-wide asteroid in the main
belt region shattered into numerous fragments following a collision. This
observation marks the first time that an asteroid disruption event has
been precisely dated. The findings appear in the June 13 issue of the
journal Nature.

The main asteroid belt, a population of roaming boulders with sizes
ranging from Texas-sized rocks to tiny pebbles, lies between the orbits of
Mars and Jupiter. Asteroids in this region frequently collide, possibly
explaining why spacecraft and radar images of these bodies show them to
have irregular shapes and heavily cratered surfaces. These highly
energetic collisions provide critical insights into the physics of the
much more massive impacts that helped shape early Earth.

"One problem with studying large-scale asteroid impacts," says lead
investigator Dr. David Nesvorny, a researcher at the SwRI Boulder Office,
"is that most of these events happened hundreds of millions to billions of
years ago, long enough for collisional and dynamical evolution to have
eroded most of the telltale features that could shed light on the impact
process."

Nesvorny and SwRI team members Dr. William F. Bottke Jr., Dr. Luke Dones,
and Dr. Harold P. Levison carefully studied a cluster of asteroid
fragments called an "asteroid family," a group of large and small rocks
believed to be the leftover pieces produced by a highly energetic
collision. Dubbed the "Karin cluster," after the name of its largest
member, 11-mile-long asteroid (832) Karin, the orbits of 13 asteroids in
the cluster were tracked backwards in time using computer models. The team
found that 5.8 million years ago, all 13 bodies shared the same orbital
orientation in space, making it possible to identify them as the
by-product of a single asteroid disruption event.

"This convergence was not an accident," says Nesvorny. "Tests indicate
that the probability of finding such an orbital alignment by chance was
less than one part in a million over the lifetime of the solar system."

The relative youth and known age of the Karin cluster could help
researchers answer several important questions about asteroid geology and
impact physics. The Karin cluster serves as a natural laboratory for the
study of asteroid collisions. For example, data from this disruption event
could be used to validate computer simulations that show the effects of
large bodies colliding at high velocities.

The Karin cluster also could help researchers understand "space
weathering." The impacts of highly energetic particles from the sun, along
with micrometeorite impacts, over time have changed the optical properties
of asteroid surfaces. This makes it difficult for researchers to identify
the kinds of asteroids that produce particular types of stony meteorite
such as "ordinary chondrites." Because objects in the Karin cluster are
young and their formation age is known, further investigation of their
surface properties could provide vital clues into the nature and rate at
which space weathering modifies their surface features.

The known age of the Karin-cluster members also could help explain the
rate at which asteroids strike one another in the main belt. Because the
Karin cluster asteroids could have been given "blank slates" 5.8 million
years ago, craters formed since that time by asteroid collisions could be
used to estimate the current crater production rate in the main belt. This
information could help researchers determine surface ages of asteroids
visited by spacecraft.

The team even considers the possibility that some of the meteorites
landing on Earth today could be traced back to this breakup event. "If a
solid connection can be made between this event and some class of
meteorites collected on Earth, we could use laboratory studies of these
meteorites to understand the nature of asteroids in the Karin cluster,"
says Nesvorny. "Results from these studies would be equivalent, in many
ways, to a spacecraft sample return mission, thus fulfilling a long-time
NASA science objective." Moreover, the SwRI team believes that the Karin
cluster may be a source region of the asteroidal dust daily accreted in
large amounts by the Earth from outer space.

NASA provided funding for the program. The paper "The Recent Breakup of an
Asteroid in the Main-Belt Region," by Nesvorny, Bottke, Dones, and Levison
appears in the June 13 issue of Nature.

Editors: For an diagram of the asteroid breakup, click here:

http://www.swri.org/press/breakup.htm

For more information contact Maria Martinez, Communications Department,
(210) 522-3305, Fax (210) 522-3547, PO Drawer 28510 San Antonio, Texas
78228-0510.
Received on Thu 13 Jun 2002 11:38:10 AM PDT


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