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

From: Robert Verish <bolidechaser_at_meteoritecentral.com>
Date: Thu Apr 22 10:01:34 2004
Message-ID: <20020617223419.77454.qmail_at_web10401.mail.yahoo.com>

---------- Beginning of Quote -----------
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."
----------- End of Quote -----------

Thanks for this interesting post, Ron.

This kind of study may go a long way towards helping
us understand why the most common meteorites are "L6"
Ordinary Chondrites, even though they most likely
originated from deep within large asteroids. Maybe
PRIOR to this "breakup event", "L6" meteorites WEREN'T
the most common type that had fallen onto our planet?

Many researchers will be looking forward with keen
interest to the follow-up studies.
Bob V.

-----Original Message-----
From: Ron Baalke [mailto:baalke_at_zagami.jpl.nasa.gov]
Sent: Thursday, June 13, 2002 8:36 AM
To: robert.verish_at_jpl.nasa.gov
Subject: SwRI Researchers Identify Asteroid Breakup
Event In The Main Asteroid Belt


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.



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Received on Mon 17 Jun 2002 06:34:19 PM PDT