When Asteroids Collide

Until now simulations of asteroid collisions have proved unsatisfactory,
since a collision simulated at normal asteroid speeds produces variously
sized hunks all of whose outgoing speed from the scene of the wreck is not
enough to break free of the others. Outcomes thus generated show a large
collection of bits floating around near each other, but this does not square
with observation, such as of the asteroid families in orbit between Mars and
Jupiter.

Conversely, cranking the model to produce enough energy to spring
pieces free from the crash site means colliding the bodies at such high
speeds that no big fragment would survive. This also contradicts observable
reality. Researchers from the CNRS’ Cassini Laboratory (Côte d’Azur
Observatory) in Nice in collaboration with colleagues from the University of
Bern and the University of Maryland have developed more sophisticated models
yielding convincing demonstrations of how asteroid families are the result
of collisions of larger bodies.

By building in the breakup of the original
bodies and the gravitational dynamics occurring among the resulting
fragments, the new simulation tells a new story. Collision results in
smithereens, the bits possess enough energy to move away from each other,
until gravitational forces bring them together in new formations, some big
some small, which travel in orbit as a kind of quasi-dispersed herd, just as
asteroid families in fact do.

The model even calls for some of the larger of
the asteroids thus formed to acquire satellites, thus providing further
corroboration from observation. This model therefore predicts that asteroids
above a certain size (a half-mile across) are likely to be conglomerates and
not monoliths. Besides providing insight into smaller heavenly body
formation these results even have an answer for waggish questions about
practical application: when pursued they will likely yield estimates of the
force needed to deviate an earthward bound asteroid (is that Orson Welles on
the radio?) from its path.

(CNRS Communiqué, November 22, article published
in Science, November 23)