Astronomy Principles and Practice Fourth Edition.pdf

192 Celestial mechanics: the many-body problem
Figure 14.5. (a) The amplified effect of a small angular error ɛ in the desired angle θ if the cue-ball is to rebound
from a fixed ball B 1 of radius R and strike a second fixed ball B 2 , rebounding from it, in turn, to strike a third
fixed ball, B 3 .(b) Magnification of (a) to show the rebound of the cue-ball from the fixed ball B 1 , the error is now
of the order 2dɛ/R.
orbit colliding with our planet. The consequences are now well understood. A collision of an asteroid
only 1 km in diameter would cause world-wide catastrophe. One 10 km across would destroy about
90% of all living species. Since there are many such asteroids and comets and their orbits are such
that they will have close encounters with one or more planets, their orbits are chaotic and, once found,
require constant monitoring to separate the potential civilization destroyers from the others.
The collision of the 22 fragments of Comet Shoemaker–Levy with the planet Jupiter in 1994 is
just one piece of evidence supporting the view that such a hazard exists. The object that is going to
destroy humanity is out there now: we do not know where it is or when it is going to fall like Nemesis
from the skies.