EXTRATERRESTRIAL IMPACTS
Extraterrestrial impacts refer to asteroids and comets striking the earth’s surface intact.
Historical evidence of impacts, such as the one that extinguished the dinosaurs 65 million
years ago and drove 70% of all species into extinction or the catastrophe at the end of the
Permian (245 million years ago) where over 90% of all species were snuffed out in a
moment of time clearly demonstrate their incredible world wide destructive power. Their
potential devastation to modern day civilizations is no less dangerous, and merits a closer
inspection of the effects of such an occurence. For simplicity only the effects of a 1 to 2
kilometer impact is discussed since the danger from smaller impacts is considerably less
and the danger from larger impacts is total extinction. The affects on both the atmosphere
and surface of the earth are examined in the following.
HISTORY
Gasses condensing out of the early Solar System not only created the planets but literally
millions of much smaller bodies commonly refered to as planetesimals or minor planets.
We know these objects from common literture as Asteroids and Comets. Though
fundamentally different in composition both orbit the sun in unstable elliptical orbits that
are often perturbed by the gravitational interaction from the larger planets and when they
collide with other planetesimals. As the Solar System evolved the bulk of these
planetesimals were either swept up by the planets in a barage of impacts, or ejected from
the Solar System. Those that remain, however, pose a serious threat to the stability of the
Earth and life as we know it.
Statistical analysis of historical records seem to indicate a major impact of a 1-kilometer
asteroid on Earth about once every 100,000 years. Depending on where it struck, an
impact of this latitude would easily devastate much of life as we know it. Anything
larger, in the 2 to 10 kilometer range, would decimate Civilization everywhere on the
Planet. Anything above 10 kilometers would eliminate all forms of life everywhere on the
planet’s surface, including the oceans. A scenario often referred to as “total extinction”.
Computer stimulations of a 1 to 2 kilometer asteroid striking the earth at approximately
20 to 25 kilometers per second and examination of historical data, especially data
centered around the extinction of the dinosaurs 65 million years ago by a 6 kilometer
comet yeild the following effects.
AIRBLAST
As the asteroid enters the upper atmosphere at supersonic speeds, the air, unable to move
out of the way, begins to pile up in front of the object. As the asteroid penetrates into the
deeper layers, the atmospheric density increases, and begins to form a shockwave ahead
of the asteroid. When the asteroid strikes the earth, the inherent potential energy bond up
in the shockwave front is transformed into kinetic energy as it plows into the surface. The
resulting physical impact of the incoming shock wave, the asteroid behind it and the
surface materials at point of impact vaporizes the asteroid and surrounding surface
materials. The sudden transformation of solids into gases release an explosion that
combines with the expanding shockwave to produce a hot air blast travelling outward and
upward at high speed.
The lateral portion of the air blast travels across the surface with a speed sufficent to
destroy everything within a 1000 mile radius.
THERMAL RADIATION & FIRE
The effect of the combined velocity and mass of the incoming asteroid literally punches a
hole in the atmosphere as the air is pushed aside. As a result, a column of reduced air
pressure is created behind the asteroid, and extends all the way up to the upper
atmosphere. On impact, a large portion of the vaporized material as well as some of the
shock wave is sucked up into this rarefied wake and injected into the upper atmosphere
where its dispersed around the globe by high speed winds.
Two characteristics mark this ejected material. First, since it consist predominantly of
vaporized material, it’s extremely hot. In the neighborhood of several thousand degrees.
Second, as it encounters the thinner upper atmosphere, it becomes transparent as it
spreads out, enhancing its radiation properties. You might think of it as a very large grill
turned up to high encircling the earth. Radiating downward, the surface of the earth is
heated to a very temperature by this ejected, vaporized material, as much as 1000
centigrade. The result is fires igniting spontanously around the earth. The only portion to
escape this scenario would be the area immediately surrounding the impact site where the
air blast would blow out the fires.
DUST CLOUDS
Ahead of the vaporized portion of the impact site, the expanding shockwave would
compress the underlying rock to a very high density. As the shockwave passed the
compressed rocks would rebound with a violent force, ejecting as much as 100 times the
total mass of the asteroid into the atmosphere.
The larger particles and boulders would fall back to Earth within 3 to 4 diameters of the
crater while the finer particles would reach the upper atmosphere with some actually
escaping into space. The resulting effect would blanket the earth with a fine dust.
Combine this dust layer with the rising clouds of soot from the fires and you have an
atmosphere that is virtually translucent to the suns rays. Darkness surrounds the globe
and temperature’s begin to fall.
ACID RAIN & OZONE DEPLETION
Nitrous oxide is produced by shockwaves as they transform the chemical properties of
the air ahead of the shockwave. With an impact of this magnitude, very large amounts of
nitrous oxide would be produced both at lower and upper levels of the atmospere. In
addition, the chemical compositon of soot reacts with the atmosphere producing other
acidic chemicals such as sulfuric acid. The combination of the two produce a very potent
acid rain on virtually every part of the planet. The acid rain changes the PH value of the
ocean waters which in turn affects all life living in the oceans. On land, the acid rain
effectively kill’s much of the remaining plant life and thoroughly acidifies the soil.
In addition to the life threatening effects of acid rain, the nitrous oxides in the atmosphere
have the unfortunate effect of destroying the ozone shield, the shield that protects the
surface of the earth. What was left of life would easily be destroyed by dangerous
radiation from the sun.
TSUNAMIS
If the asteroid had the unfortunate luck of impacting in the ocean (which is likely since
the ocean covers 70% of the earths surface), the resulting shockwave would push the
ocean water aside, creating a very large hole. Causing a large spike of water in the center
of the hole, the waters would rush back in to fill the hole and overrun the original
diameter of the hole as the shockwave passed.
A tsunami, which is a large undersea wave generated by shock or sudden movement, is
caused by this initial shockwave and is followed by reduced tsunami’s resulting from the
inundations in the water as it oscilates back into the hole.
As the tsunami approaches land, the undersea wave begins to pile up (much like a regular
wave) as the shallower continental shelf is approached. The wave builds to tremendous
heights as it strikes land devasting anything living along the coast. For an 1 to 2 kilometer
asteroid impacting the ocean, the tsunami height might reach 2000 to 3000 meters as it
reached land. That would wipe out the east coast all the way to the Appalachian
mountains.
In addition to tsunamis, the column of water vapor lifted into the atmosphere though the
wake would significantly raise the water content of the upper atmosphere which is
normally very low. The result would be a heightened greenhouse effect that would raise
the average surface temperature of the entire planet uniformly by as much as 10 to 15
degrees centigrade. Even if the resulting increase were less than the predicted 10 to 15
degrees, the effect on both plant and animal life would be globally devastating over the
long-term.
DEATH TOLL
Depending on whether the asteroid struck land or water, the death toll of a 1 to 2
kilometer asteroid could be estimated in the billions, perhaps 1 to 1.5 billion people
initially. Long term effects from the greenhouse effect, acid rains, ozone depletion and
destruction of the photosynthesis cycle could easily wipe out another 1 to 1.5 billion.
The devastation would be most severe in 3rd world countries where starvation and
exposure would decimate most of there populations.