In honor of the recent meteorite strike in Russia, I offer my Astronomy class term paper from spring semester, 2012 at PNC.
What would it be like to be one minute
sitting peacefully on your porch, and the next feeling as though your shirt
were on fire, while simultaneously being knocked from your chair? What if your
location was over 40 miles from the center of the action that caused these
things to happen?1
An eyewitness to one of the most powerful
natural catastrophes ever unleashed on the earth, the Tunguska Meteor Impact
painted a picture in vivid detail of what transpired on June 30, 1908 at 7:17
in the morning. Also of significance, is that this incident took place during a
time when science was beginning to generate sophisticated theories on many
natural phenomenon; the century’s unbridled technological march fostered the
development of the tools to verify these hypotheses. Finally, man-made devices
were built later in the century that could in many ways replicate the power of
occurrences that had aroused man’s curiosity for thousands of years.
The devastation wrought on this
remote corner of Siberia, was caused by one of the best documented asteroid
strikes in human history. Included in the damage tally was more than 800 square
miles of leveled forest, consisting of some 80 million trees. The force
required to cause this amount of damage has been compared to the destructive
power of 185 Hiroshima bombs. This last claim had to wait until 37 years after
the event, when a comparison could be made to the man-made device that fostered
the end of hostilities of World War 2. The parallels between the catastrophes
are hard to ignore: both Tunguska and the Hiroshima were subjected to an “air
burst.” That is the bomb’s detonation, and the speeding asteroid’s eventually
succumbing to friction and exploding occurred some distance above the ground, in
the case of the space rock, around 5.5 miles. This would account for the
statement of eye-witnesses, one of which characterized the sight as “the whole
northern part of the sky covered by fire.”2
When researchers were finally
able to examine the remote Siberian sight in 1927, they didn’t have much trouble
pinpointing the center of the blast, as trees were felled in a circular pattern
for miles around thus pointing the way. 3The damaged growth lay in a
radial orientation except for the very center, where the trees were still
upright, but with horizontal branches missing. This very same pattern was also
observed years later at the Hiroshima sight.3
The particulars of the Tunguska asteroid
were an 1100 ton rock travelling at 33,500 miles per hour. The great speed and resulting friction heated
the air to 44,500 degrees Fahrenheit. The combination also caused the rock to “pancake,”
or flatten out. This in turn created more friction, a greater flattening effect,
eventually causing a violent explosion before hitting the ground. This last detail
is significant as there was no impact crater; the rock simply vaporized in
mid-air. The damage on the ground is a result of a powerful shock wave driven in
the explosion’s wake.4
As previously stated, the area
affected is so remote that it was a full nineteen years before a scientific
research team was able to reach the site. But even with this long intervening
interval of time, there was still a wealth of evidence to be analyzed; the
pattern, and type of damage to the trees sustained being among the most useful.
Additionally, seismic readings from the day of the event were available from
places as far away as London. This data also provided vital clues as to the
power of the strike.5
The importance of eyewitness
testimony cannot be overstressed. Many previous strikes occurred in uninhabited
areas such as oceans, or other less populated regions. Siberia is not exactly a
population center, but people do live there.
However, at the onset many residents were reluctant to talk, as they
believed that the strike was a visitation from the gods, as punishment for some
deficiency on their part. When he
finally broke his silence, the man who was knocked from his chair had harbored
feelings for almost two decades that were representative of those held by many
other witnesses.6
A primary area of discussion
between experts in recent years has been how to correlate the explosive force
of an asteroid, to a bomb being detonated. And while there are similarities,
the differences are great enough to render a direct comparison difficult to
assess. Total power estimates of the
Tunguska explosion have run from 3 to 700 megatons, quite a large range. The
number that most scientists agree is closer to the true level is on the low
end, around 3 to 5 megatons. This is still a very powerful blast, but much less
so than the 15 megaton figure that was generally accepted for many years. As a
practical matter, this information is vital in predicting the frequency and
potential devastation of future strikes. The fact that the Tunguska event
occurred in a largely uninhabited region is not lost on modern observers. If
such an event were to take place in a population center, the death toll could
run in the millions, with a correspondingly high loss of property.7
A
somewhat troubling dynamic is that events on the lower end of the scale occur
with much greater frequency (as often as every 400 years) than on the upper end.8
So while the potential damage may be
relatively smaller in magnitude, the likelihood of an event is much greater.
This makes predicting and planning for contingencies all the more important.
One element that does work in mankind’s favor is that while the population of
the earth is much larger than in 1908, most of the people are concentrated in
relatively few areas. Recently, news stories relating to asteroid 2012 DA14
prominently mention Tunguska. This
medium-sized rock will pass by the earth in February of 2013, much closer than
many satellite’s orbital paths. Fortunately, not close enough to pose any
danger, but it is interesting that even after more than a century has passed
since Tunguska, the connection is still there.9
Another asteroid strike, this one
some 65 million years ago is thought to have been responsible for the demise of
the dinosaurs. Like the Siberian event, there is also a trail of tell-tale
evidence pointing scientists to exactly where it occurred, the Yucatan region
of Mexico. But this is where the similarities end. The ancient strike was not
an air-burst; a 100 mile-wide crater that is still partially visible attests to
this.10 From intense research science has constructed many theories
as to what happened, and not surprisingly, there is a fair amount of disagreement.
But one thing is certain; asteroid strikes of the Tunguska magnitude or greater
have the potential to greatly alter life on earth as we know it. The hope is
that we will be ready to deal with the aftermath, whatever form it takes, and
hopefully fair better than the great prehistoric beasts did.
Notes
1.
Dr. Tony Phillips “Tunguska Impact--100 Years Later”
NASA Science, March 8, 2012
2.
Amir
Alexander “The Tunguska Riddle: How Powerful was the Greatest Asteroid Impact
in Recorded History?” The Planetary Society, March 11, 2012
3.
Amir
Alexander “The Tunguska Riddle,” March 11, 2012
4.
Ibid.
5.
Dr. Tony Phillips “Tunguska Impact,” March 11, 2012
6.
Ibid
7.
Amir Alexander “The Tunguska Riddle,” March 11, 2012
8.
Ibid.
9.
Mike Wall “Mid-Size
Asteroid Won't Hit Earth in 2013,”March 11, 2012
Leslie Mullen “Do We Know What Killed the
Dinosaurs?” March 11, 2012
