Killer Asteroids
Killer asteroids are not just the invention of disaster movies. Asteroid
strikes are real possibilities, and they have actually happened in the past. The
chances are small that we will get hit, but if the asteroid was large enough, it
could do enough damage to end life on Earth.
Many scientists believe that a collision with an asteroid or a comet may have
been responsible for the extinction of dinosaurs. A giant crater on the Yucatán
Peninsula in Mexico marks the spot where a comet or asteroid struck Earth about
65 million years ago. This is about the same time as the disappearance of the
last of the dinosaurs. A collision with an asteroid large enough to make the
Yucatán crater would have sent so much dust and gas into the atmosphere that
sunlight would have been blocked for months or years, killing much of Earth’s
vegetation and interrupting the food chain the dinosaurs depended on.
The most recent major encounter was in 1908 in Siberia. The force of the
encounter flattened over 500,000 acres of pine forests and killed thousands of
reindeer.
Asteroid Belt
Most asteroids are in the Asteroid Belt between the orbits of Mars and
Jupiter. It is the home to thousands of small, rocky bodies that orbit the
Sun.
These asteroids are also called "minor planets," and they are thought
to be remains of a planet that tried to form millions of years ago.
An asteroid can leave its orbit and travel into the inner solar system. This
change may be caused by a collision with another asteroid, the gravitational
pull from Mars, or the Sun’s heat.
Tracking Down Asteroids
In 1995, NASA and the U.S. Air Force began a project called Near-Earth
Asteroid Tracking (NEAT). NEAT has an observatory in Hawaii to search for
asteroids with orbits that might threaten Earth. Astronomers have found more
than 200 asteroids with orbits that cross Earth’s orbit. Some scientists think
several thousand of these Earth-crossing asteroids may exist and that as many as
1,500 could be large enough to cause a global disaster if they collided with
Earth. Still, the chances of such a collision average out to only one collision
about every 300,000 years. Astronomers believe that tracking programs like NEAT
would probably help the world by giving us decades or even centuries of warning
time before the asteroid hits.
Scientists have suggested several strategies for knocking asteroids off their
course. If the asteroid is far enough, we could use a nuclear warhead to blow it
up without much danger of pieces of the asteroid causing significant damage to
Earth. Another way is to attach a rocket engine to the asteroid and direct the
asteroid off course without breaking it up. Both of these methods require that
the asteroid be far away from Earth. If an asteroid exploded near Earth, chunks
of the asteroid would probably still cause major damage. Any effort to push the
asteroid off course would also require years of work. Asteroids are much too big
for a rocket to push quickly.
Level of Asteroid Damage
|
Type of Damage |
Size of Asteroid |
Chance of Occurring |
Damage |
|
Local Damage |
Up to 200 yards in diameter |
One to ten per century |
Could cause local damage, but no lasting environmental
effects |
|
Widespread Devastation |
200 yards to 1 mile in diameter |
One every 10,000 – 1 million years |
Could blast a crater up to 10 miles wide with worldwide
environmental effects (for example, loss of season’s crops) |
|
"Impact" Winter |
1-10 miles in diameter |
One every 1-100 million years |
It would create a crater 100 miles across. Dust cloud
from impact would contaminate atmosphere, resulting in a "nuclear
winter" that could last for several years |
|
Doomsday |
Over 10 miles in diameter |
Fewer than one every 100 million years |
Loss of most life forms on Earth as a result of
prolonged "impact winter" and ice age |
