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

METEORS, METEOROIDS, AND METEORITES, OH MY! 139
There are teams of astronomers across the world looking for
potential Earth impactors. They patiently scan the sky night after
night, looking for the one faint blip that moves consistently from
one image to the next. They plot the orbit, project it into the
future, and see if our days are numbered.
No one has found such a rock yet. But there are a lot of rocks
out there. . . .
Suppose that sometime in the near future the alarm is pulled.
An asteroid as big as the Dinosaur Killer is spotted, and it will
soon cross paths with us. What can we do?
Despite Hollywood’s efforts, the answer is probably not to
send a bunch of wisecracking oil riggers in souped-up rocket ships
to the asteroid to blow it up at the last second. That may have
worked in the 1998 blockbuster Armageddon, but in real life it
wouldn’t work. Even the largest bomb ever built would not disintegrate
an asteroid “the size of Texas.” (Not that Armageddon
was terribly accurate in anything it showed; about the only thing
it got right was that there is an asteroid in it, and asteroids do indeed
exist.) In the same year, the movie Deep Impact depicted a
comet getting shattered by a bomb shortly before it entered the
Earth’s atmosphere. That’s even worse! Instead of a single impact
yielding an explosion of billions of megatons, you’d get a billion
impacts each exploding with a yield of many megatons. In his fascinating
book, Rain of Iron and Ice (New York, Helix Books, 1996),
University of Arizona planetologist John Lewis calculates that breaking
up a moderately sized asteroid can actually increase the devastation
by a factor of four to ten. You’d spread the disaster out over
a much larger area of the Earth, causing more damage.
If we cannot blow it up, then what? Of course, the best option
is for it to miss us in the first place, so we’d have to shove it aside.
The orbit of an asteroid can be altered by applying a force to it. If
enough time is available, like decades, the amount of force can be
small. A larger force is needed if time is short.
There are several plans for pushing such rocks out of the way.
One is to land rockets on the surface and erect a giant solar sail.
The sail, made of very thin Mylar with an area of hundreds of
square kilometers, would catch the solar wind and also react to the