 |
|
|
|
|
|
A 1 kilometer asteroid probably strikes the Earth every few
million years, while a global killer on the order of 5-10
kilometers strikes the Earth every few hundred million years. A
100 meter asteroid may strike the Earth every thousand years
(Cooke, 2004). In fact, in 1908, a 60 meter asteroid exploded in
the upper atmosphere over a remote area in Eastern Siberia
(Tunguska) and flattened trees for thousands of square miles. A
high-velocity impact of a 2 kilometer asteroid with the Earth
could kill a billion people. A ten kilometer asteroid impacting
the Earth could extinguish us as a species (Foster, 2005). The
odds of the Earth suffering a catastrophic collision with an
asteroid over the next century is roughly estimated at 1 in 1500
to 1 in 5000 (Schultz, 2001). The probability of being killed by
an impact event is very small on the order of 1 in 10,000 to
1/100,000. Driving and overeating are far bigger risks to the
average individual.
Impacts by smaller objects are much more common than those of
large objects. Smaller objects could produce destructive
tsunamis, directly strike a large city, or explode over a large
populated area killing millions of people. Fortunately, the
Earth’s atmosphere provides an increasingly protective role as
objects become smaller. Most meteoroids fragment into small
relatively harmless pieces as they travel through the atmosphere
at high speeds. Even a very solid mainly metallic asteroid
fragment probably needs to be 100 meters in diameter for it to
survive passage through the atmosphere intact (Cooke, 2004).
Satellites operating for the United States Department of Defense
have been monitoring the Earth for nuclear weapons and missile
launches for several decades. Their sensors in visible and
infrared light can detect flashes of light from meteoroid
atmospheric impacts. Five kiloton equivalent (Hiroshima atomic
bomb size) impact events occur in the Earth’s atmosphere every
year, but we are saved from harm by the Earth’s atmospheric
blanket. |
|
|
BACK |
NEXT |
|
Back to Top | Essay List |
|
