[meteorite-list] Simulations Of Collisions Shed Light On The Internal Structure Of Asteroids

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:23:44 2004
Message-ID: <200303041731.JAA07336_at_zagami.jpl.nasa.gov>

Centre National de la Recherche Scientifique
Paris, France

Researcher contact:
Patrick Michel
Observatoire de la Côte d'Azur
e-mail: michel_at_obs-nice.fr
Tel: +33 4 92 00 30 55

Contact INSU:
Philippe Chauvin
e-mail: philippe.chauvin_at_cnrs-dir.fr
Tel: +33 1 44 96 43 36

Press contact:
Martine Hasler
Tel: +33 1 44 96 46 35
e-mail: martine.hasler_at_cnrs-dir.fr

February 6, 2003

Simulations of collisions shed light on the internal
structure of asteroids

An international team of researchers led by Patrick Michel
(Observatoire de la Côte d’Azur – CNRS, Nice) have carried
out simulations of asteroid collisions. For the first
time, such simulations have made it possible to provide
information about the internal structure of asteroids and,
in particular, have shown that the parent bodies from
which asteroid families have originated must have been
fragmented (and non-monolithic) bodies or stacked rocks.
The formation of an asteroid family results from the
break-up of such a body, which creates hundreds of
thousands of fragments, certain of which could become
dangerous asteroids and meteorites. These findings also
show that the impact energy during a collision is highly
dependent upon the internal structure of the target;
this information is very useful for the development of
a strategy of defense against the threat of an impact
with the Earth. The researchers' results are published
in the February 6, 2003, issue of Nature and are
featured on the journal's cover.

In the asteroid belt, which is located between Mars and
Jupiter, asteroid families are concentrated groups of
small bodies that share the same spectral properties.
More than 20 families have been identified, each family
believed to be fragments resulting from the break-up
of a large parent body in a regime where gravity, more
than the material strength of the rock, is the key
factor (*). The actual size and velocity distributions
of the family members provide the main constraint for
testing our understanding of the break-up process in
this gravitational context. A new asteroid family,
which bears the name of its largest member, Karin, was
recently identified and studied. It is the youngest
family discovered to date, and appears to have resulted
from a collision around 5 million years ago. This
family provides a unique opportunity to study a
collisional outcome that is relatively unaffected by
phenomena such as collisional erosion and the dynamic
diffusion of fragments, which, over time, alter the
properties resulting directly from the collision.

Patrick Michel of the Cassini Laboratory (Observatoire
de la Côte d’Azur – CNRS) and two of his colleagues
from the Universities of Bern (Switzerland) and
Maryland (USA), have developed numerical simulations
of collisions with the aim of determining the classes
of events that make it possible to reproduce the main
characteristics of the Karin family. As the results
depend to a large degree on the internal structure
of the parent body, they were able to show that this
family must have resulted from the break-up of a body
that was originally full of fracture and/or empty
zones, rather than a purely monolithic body. Their
findings moreover indicate that all the members of
this family are aggregates formed by the gravitational
re-accumulation of smaller fragments, and that certain
of them could have been ejected on trajectories that
cross the Earth's trajectory. Since those families that
are already known and the oldest families share similar
properties, the authors suggest that they are likely
to have had a similar history.

This information concerning the internal structure of
large asteroids also has consequences for the impact
energy that would destroy them. This is useful not
only to estimate the lifetime of these objects in the
asteroid belt, but also in order to develop strategies
that aim to redirect such a potentially dangerous
asteroid.

Reference:
P. Michel, W. Benz & D.C. Richardson, Disruption of
fragmented parent bodies as the origin of asteroid
families, Nature Vol. 421, 608-611, 2003.

For more information about asteroid collisions, see:
Press release dated November 22, 2001
   http://www.cnrs.fr/cw/en/pres/compress/collisionsAsteroides.htm
Received on Tue 04 Mar 2003 12:31:33 PM PST