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Mathilde - part 1 of 2

Hi folks,

Now that the list is up and running again, let's get back to work :-)


Astronomy, October 1998, p. 26:

Impact Hazard, Blasting Asteroids - It's tough to blow up space rocks

An asteroid hurtles through space on a collision with Earth. What would
you do? Most people would exclaim, "Blow it up!" But Erik Asphaug of the
University of California at Santa Cruz, and his colleagues, would shake
their heads "no. " Their recent study of  mile-sized asteroids,
published in the June 4 issue of Nature, shows that they aren't so easy
to disrupt. "It's a lot more difficult to nudge these asteroids than we
had thought," says Asphaug, who used computer simulations to study the
effects of explosions on three different kinds of asteroids.
Earlier studies suggested that asteroids aren't solid bodies but rather
loose clumps of debris held together by gravity. The new simulations
show that if a large body impacts an asteroid, the damage remains
localized. For example, imagine trying to break up an entire sand dune
by smashing one end of it with a hammer. You'll create a nice crater,
but the dune will barely move.
To complete the research, Asphaug and his colleagues began with a
peanut-shaped asteroid with three different structures: solid rock, a
pair of solid rocks, and a rubble pile. The team hurled house-sized
rocks at each asteroid and measured the devastation.
Asteroids made from solid rock shatter into smaller pieces, but they
don't always disperse. They may break into several large pieces or form
a cluster of debris. Asteroids made from a pair of rocks seem to resist
impacts because one of the rocks absorbs most of the shock from the
impact. And rubble-pile asteroids seem even less affected.
Asphaug's work may explain observations of the asteroid Mathilde. Images
from the Near Earth Asteroid Rendezvous spacecraft revealed old craters
apparently unscathed by newer impacts nearby. Mathilde was also pocked
by craters larger in diameter than the asteroid itself. If Mathilde is
unaffected by such tremendous impacts, then a similar asteroid would
probably shrug off any nuclear bomb we threw at it. "More work needs to
be done before we can decide whether nuclear warheads provide a viable
deterrent, " says Asphaug.

Best wishes,

Bernd



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