Bad Astronomy: Misconceptions and Misuses Revealed, from ...

140 SKIES AT NIGHT ARE BIG AND BRIGHT
minute pressure of sunlight. It would impart a gentle but constant
force, moving the rock into a safer trajectory.
Another plan is more blunt: attach rockets to the asteroid and
use them to push it. This has the engineering difficulty of just how
you’d strap boosters to a rock in the first place.
Ironically, Hollywood came close to another good plan. Instead
of blowing the rock up, we use nuclear weapons to heat the asteroid.
Again, in Rain of Iron and Ice, Lewis finds that a small nuclear
explosion (he implies a yield of about 100 kilotons) would suffice.
Exploded a few kilometers above the surface, the intense heat of the
explosion would vaporize material off the surface of the asteroid.
This material would expand outward, and, like a rocket, push the
asteroid in the other direction. Lewis mentions that this has two
benefits: it prevents the impact, and also removes a nuclear weapon
from the Earth. This is the favored method of all the people who
have studied it.
All of these methods have a subtle assumption attached, that
we understand the structure of asteroids and comets. In reality, we
don’t. Asteroids come in many flavors; some are iron, some stony.
Others appear to be no more than loose piles of rubble, barely
held together by their own gravity. Without knowing even the
most basic information about asteroids, we are literally shooting in
the dark.
As with most problems, our best weapon is science itself. We
need to study asteroids and comets, and study them up close, so
that we can better understand how to divert them when the time
comes. On February 14, 2000, the NASA probe Near Earth Asteroid
Rendezvous entered orbit around the asteroid Eros. The amount
learned from the mission is astounding, such as the surface structures
and mineral composition of the asteroid. More probes are
planned, some of which are ambitious enough to actually land on
asteroids and determine their internal structure. We may yet learn
how to handle dangerous ones when the time comes.
There is an interesting corollary to all this. If we can learn how
to divert an asteroid instead of merely blowing it up, that means
we can steer it. It may be possible to put a dangerous asteroid into
a safe orbit around the Earth. From there we could actually set up