Today, asteroids, real and imagined. The University
of Houston's College of Engineering presents this
series about the machines that make our
civilization run, and the people whose ingenuity
Two articles in a recent
Science magazine deal with the threat to
Earth by asteroids and meteorites. The first is
about a NASA-sponsored workshop on asteroids. So
far, NASA has searched out 635 asteroids larger
than a kilometer across. However they estimate that
almost twice that number might be out there,
orbiting the sun.
They hope to have ninety percent of those really
big asteroids identified by 2008. The
mile-and-a-half by three-mile asteroid
Toutatis (large enough to've eliminated
human life on Earth) had us concerned for a while.
We finally determined that it'll miss Earth by a
"mere" million miles in 2004.
Of course, NASA's catalog of large asteroids
doesn't begin to capture the tens of thousands of
smaller objects out there. They include asteroids
that could obliterate major cities or launch
three-hundred-foot tidal waves.
So how serious is this threat? History
answers that question: Asteroids a kilometer or
more across have hit Earth every few
hundred-thousand years, rearranging the balance of
species when they do. Asteroids as large as
two-tenths of a mile in diameter hit us every sixty
thousand years. So the problem is real enough, even
if we're very unlikely to see a major collision in
Still, the consequences would be so horrific that
we'd be crazy to ignore such catastrophes. And here
the fun begins: What means should we pursue to
We can't rest on any one-size-fits-all solution.
Some asteroids might be blown up and scattered.
Others might have to be nudged into a new orbit by
some sort of jet. Some are tight clusters of loose
rock. I'll leave you to think of means for
diverting something like that. The problem is real,
large, and varied.
So we turn to the other Science article.
Scientists are revisiting the Tunguska explosion.
In 1908, it flattened trees and killed herds of
animals over the thinly populated Tunguska Forest in Siberia --
roughly the area of Rhode Island. For days
afterward, the resulting dust-cloud cast an eerie
light all around the world. We estimate that the
Tunguska meteor was about ninety feet in diameter.
However, the blast left no crater. It seems to've
occurred five or six miles up, and the forest
directly below was left untouched. Furthermore, no
meteorite fragments were ever found. It is a story
that somehow never quite added up.
It turns out that a huge natural-gas deposit lies
directly below the blast site. Now these scientists
wonder if a large gas leak from the deposit could
have combined with the right atmospheric conditions
to create an immense gas bomb.
And so nature is large. It has the capacity for
turning upon us from without or from within. To
stay alive, we must (as we always have) employ an
ongoing and aggressive curiosity about the
immensities of all that is around us.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
Kerr, R. A., A Little Respect for the Asteroid
Threat. Science, Vol. 297, 13 September
2002, pp. 1785-1787. See also, More Theories on
Tunguska. Science, Vol. 297, 13 September
2002, pg. 1803.
For more on the problem of orbiting space junk, see
Four views of the asteroid Toutatis
(Image courtesy of NASA)
The Engines of Our Ingenuity is
Copyright © 1988-2002 by John H.