A near
earth Object (NEO) does not need to be
large to devastate.
One the size of a small garage would annihilate a large city. One big
enough to leave a 10km crater, still nowhere near the size of the
biggest (there is a 300km crater on Earth), would have the destructive
force of every one of the world's 10,000 nuclear warhead combined.
The Asteroid that destroyed the Dinosaurs
It is
thought that 65 million years ago in
what is now Yucatan the impact at a velocity of 11 km/second of a
10-kilometer wide asteroid is what helped to bring about the K-T
extinction, whereas no land animal with a size greater than the size of
a small chicken was able to survive. Those that study
this time frame believe that if man had inhabited the
planet at this time, he surely would have been destroyed by this
particular event. This event threw huge amounts of matter into
the atmosphere in addition to this, it caused 2000 foot waves that may
have all but completely emptied the Gulf of Mexico. This event created
months of darkness (which interfered with photosynthesis) and much
cooler temperatures globally, and the resulting harsh conditions which
in turn led to the extinction of many species, including the last of
the dinosaurs.
Although this is
quite compelling as a hypothesis, it remains
controversial and has broad but not total acceptance within the
scientific community. It is an estimate that impacts of asteroids as
large as the one thought responsible for the K-T extinction occur about
once every hundred million years.
Documented & Studied Impacts and Events
On the
date of June 30th, 1908, at about a
quarter after 7:00 a.m., a very mysterious explosion occurred in the
skies over Tunguska, Siberia, located in Russia. This explosion
happened at anywhere between six-to-eight kilometers from ground zero,
and the resultant action in this was to lay waste to a vast region of
pine forest of 2,150 square kilometers, felling more than 60 million
trees. This was seen as a brilliant burst of light from the
inhabitants of the region of 50 kilometers around. Witnesses
claim that the explosion was so loud and powerful as to blow-out
windows, temporarily blind and knock people to the ground, and sounded
like a deafening roar. Had it happened fifty years later, it is
surmised by scientists, (placing it within that time-frame of the
Cold-War) it would most likely have spurred that nation into a nuclear
war.
In 1972, an
estimated 1000-ton object skimmed upon the edge of Earth's
atmosphere over the Grand Tetons National Park in Wyoming, and then
skipped back out into space, like a skimming-stone off water. This event was
photographed by tourists and also was detected by Air
Force satellites. Had it approached at a 90° angle into the
atmosphere, it most likely would have caused a Hiroshima-scale
explosion over Canada, only a bit down-sized from the scale of the
Siberian blast.
In 1992, a
meteorite weighing 12.4 kg. was recovered after it had made
a spectacular appearance over Peekskill, N.Y., where it was described
as being as bright as a "full-moon". This event was recorded by 16
separate video cameras, some of which were located at a local
high-school football game and were recording the game!
On January 19,
1993, a very bright asteroid crossed the sky of Northern
Italy, ending with an explosion approximately over the town of Lugo,
Italy. The explosion (14 kilotons of energy) generated shock
waves which were recorded by six local seismic stations. This
particular type of asteroid did disintegrate at a great altitude, which
is quite lucky for the town of Lugo. Had it been an the type of
asteroid that would have been composed mostly of iron ferrites, of
which only some 6% of all asteroids are known to be comprised as such,
chances are that it would have disintegrated at a much lower altitude
creating a great deal of death and destruction.
In 1994 the US
Department of Defense made public domain its records on
energetic bolide-type asteroids over a time span of about twenty years.
This data indicates that, from 1975 to 1992, there were 136 airbursts
of energy greater than 1 kiloton, but the real number was probably at
least 10 times higher, because the satellite system does not cover the
entire surface of the Earth.
What would happen during a large collision?
In 1994 a
large comet (P/Shoemaker-Levy
9) hit
Jupiter. The
Hubble telescope recorded the
impact with tremendous
accuracy. As it entered the atmosphere of Jupiter temperatures reached
over 20,000 degrees. The impact sent a fireball thousands of miles into
space. [Image compliments of the-planet-jupiter.com. A magnificent
artist rendering of Shoemaker-Levy
9 breaking up, and impacting
into
Jupiter] The scale of the impact may look small in scale, but bear in
mind the size differential between Jupiter and Earth.
The damage
of an impact on Earth would kill all life. Massive
earthquakes would jet out around the globe at thousands of miles an
hour, destroying all buildings and life in their path. It would also
trigger volcanic activity setting off eruptions and explosions all over
the world. An enormous dust cloud would be sent into the
atmosphere. A fireball would be sent into the sky miles
tall. Any life that had survived the inital impact would be overcome
with a whole new set of problems. Peices of the earth and dust would
block the atmosphere, preventing the earth from getting any sun. Plant
life would become extinct, and humans would face the horrifying reality
of a nuclear winter.
How many asteroids do we have to worry about?
Hundreds...
thousands. The largest yet
discovered are an awesome 18 miles in length. Scientists estimate that
there could be as many as 1000 asteroids larger than 1 mile across that
pass relativly close to Earth. An impact by any one of these would be
an Extinction Level Event.
How often is Earth hit by an asteroid?
More
frequently than you may think. An
incident like Tunguska occurs approximately once per every hundred
years. Smaller ones, but easily big enough to take out a large city,
occur at least 3 times per century, for example Brazil in 1930. While
most of the recent recorded impacts have happened in places that were
barely inhabited, we won't always be that lucky. If the Tunguska event
had happened over the city of New York it would have been nearly
leveled.
Those large
enough to cause extinction, 1/2 mile in diameter, occur
less frequently - around once per million years. No large scale
asteroids or meteors have been found to have an earth crossing path,
but the number of people looking compared to the number that may be out
there is majorly lopsided.
How could we stop an Imminent Impact?
Up until
50 years ago, we would have been
totally defenseless against one. With the advent of nuclear weapons, we
might have the possiblity of lauching ICBM nuclear tipped rockets at
it, in an attempt to destroy it. However, doing such could result in
creating a worse situation for ourselves. If we broke it into peices,
the damage from multiple impacts could be just as bad as one big one.
The other option
is to do the best we can to prepare for such an
impact. Those in the direct path of the impact would stand little
chance of survival. however, if shelters areound the world were created
to prepare for such an onslaught, with stockpiled food, water and
resources - they may be able to hold out until the dust settled.
The world they
would be coming back out to would be far different than
the one they left. With nearly every species and 75-90% of plant life
possibly wiped out, humans would literally have to start all over.
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