There is much speculation about the object which crossed in 1908 the sibirian
sky as a radiant fireball. When it detonated, it destroyed more than 2000
km2 pine forest. Some claimed it must have been a big meteorite,
others suspected an alien spaceship accident. Still other people thought about
exotic objects like "black mini-holes" or a new type of volcanic activity.
Also there was discussion about new weapon tests of a "mad scientist".
It was mysterious for a long time during the 20th century what really happened
in the morning of June 30, 1908 above the sibirian Taiga. Seen from outside,
there were all traces of a big meteorite fall (the biggest of the 20th
century). Nevertheless there is not a trace of a crater. Because observers
from the region described what they saw as "white-hot fireball", "terrible
detonation", "burning heat" and "ascending smoke column" which reminds us to
the sadly well-known apperance of nuclear detonations, there soon came up
speculations if an UFO crashed in 1908. For at this time, there was not a
single nuclear apparatus on earth.
Contrary to this, "serious" scientists argued the descriptions of an
nuclear-detonation-like event aren't reliable for in 1908 there
couldn't have been a nuclear detonation - there is no trace of
radioactivity beyond the natural values in the area.
Both, UFOlogists as well as "serious" scientists, have to stand some criticism
by the opinion of the author.
UFOlogists, because not every phenomenon which reminds us humans to a
technical process must have been of alien origin. Mother Nature is quite more
ingenious than we can imagine.
"Serious" scientists, because men usually can well describe what the have seen
(observations of the Sikhote Alin meteorite fall which fit very well to the
recovered and measured traces prove that). This holds even if they due to
their cultural origin use strange words to describe. If observations and
scientific models doesn't fit, it's time to examine the scientific model and
not to drop observation reports.
It was relatively late in the 20th century when some thought if our knowledge
about meteorite falls (big meteorite equals big fireball equals big crater)
maybe wasn't that complete. Thoughts tended toward an object of volatile
material hit the earth, maybe a piece of comet ice. Again it was strange that
there was no observation of a near-earth comet in the weeks before the
Tunguska event.
Nevertheless a fragment of Encke's Comet for a long time was the best
candidate for such a scenario. But when computers got more power and the
simulations went into detail it was shown that a piece of ice would be
vapourized by far too high in the atmosphere to cause the devastations of
Tunguska.
The puzzle about Tunguska finally was solved when a known phenomenon of meteor
observations was examined theoretically - the fragmentation in flight.
Looking at it, only solid iron-meteoroides have a fair chance to reach earth's
surface in one piece. Stony meteoroides normally fragment in middle heigths,
often in severeal phases. When there were detailed enough physical models of
this behaviour (e.g. Hill & Goda, see below) the veil of mystery disappeared
from Tunguska.
Today we suppose a stony meteoriode of 80 meters diameter entered 1908 the
earth's atmosphere by a velocity of 22 km/s and an angle of 30 degrees above
horizon. Such a stony meteoroide consists of a relatively weak material; in
dense layers of the atmosphere it will fragment rapidly. Small fragments are
decelerated nearly instantaneous. Thus, nearly all of the kinetic energy of
the meteoroide (which is well in the range of a big hydrogen bomb) is released
in a short piece of its trajectory. Following up there is a detonation which
has all characteristics of a very strong nuclear blast.
For this website I have reprogrammed the Hill & Goda model which simulates the energy release during the break-up / fragmentation. The pictures base upon the computations, but note that all pictures are my personal artwork (the program has no graphics front-end). Artwork also is inspired by the pictures of Michael Light (see below). In the case one of my readers wants to play around with the program, the C source code of it I put under the GPL (General Public License) for download (see below).
The detonation cloud ascended to an estimated height of 60 km and spread about 200 km until it dissolved. In the evening and following nights luminous clouds of fine dust in the high atmosphere were watched in Europe.
It is somewhat threatening to imagine what would heve happened if the
Tunguska-meteoroide had hit the earth just a few decades later during the
"Cold War". The atmospheric effect of a mushroom cloud definitely would have
been interpreted as an enemy thermonuclear strike. A worldwide thermonuclear
war would have been followed up. Maybe, too late, a scientist would have found
out there was no radiactivity at the site of the first strike... we all lived
at knive's edge without knowing it.
In the 1970ies and 1980ies from time to time early warn satellites registered
flashes and fireballs in the earth's atmosphere which were interpreted as
illegal nuclear tests (most above sea, Israel and South Africa obscured). But
there was never a trace of a true nuclear test. It is probable that they were
of meteoroide origin, too.
One can ask what happens if still bigger stone meteoroides hit the earth. The
result of simulations is somewhat weird.
Very big (and thus very rare) asteroids of stone or iron or very big comets of
ice reach earth's surface in one piece and leave a big crater. The not so rare
small and middle-sized asteroids of stone all break up in the atmosphere where
the blast is much more effective in destruction than at an impact.
The energy of the celestial object increases much faster than one would
believe. For example, if a stony meteoroide of 200 m diameter hits the earth
at 30 km/s (which is not that far more than the Tunguska meteoroide had) it
has an energy of about one gigaton TNT (1000 megatons TNT), more than the
30fold of Tunguska. It would detonate at a height of 6 km forming a fireball
of 42 km diameter. The flash in 100 km distance would be as 10,000 times
bright as the sun. Possibly the fireball would melt a crater into the ground
even if the remains of the meteoroide never reach it.
In a circle of 140 km diameter, there would be worst devastations, in hundreds
of kilometers the effects still would affect. Due to the big distances the
shockwave would need a long time to blow out all fires. In some cases this
could mean there is already enough glowing charcoal to re-ignite. Apokalytic
firestorms on large areas would develop. A catastrophe of this kind could wipe
out a small state totally.
The fireball of the detonation would break out of the earth's atmosphere,
forming a layer of dust, smoke and gas around the earth which would weaken the
sunlight for weeks or months. A "nuclear winter" would be probable.
To start a global catastrophe, it needs no celestial body which strikes into
the earth's surface like in "Deep Impact". Common stony asteroides of middle
sizes have much more kinetic energy than biggest man-made nuclear blasts - and
they release their energy in very desastrous atmospheric explosions.
A crater isn't caused by this, but nevertheless a fireball, shock wave,
mushroom cloud and their destructive follow-ups are similar to a big
thermonuclear detonation. Just radioactivity is not released.
The Tunguska event of 1908 no longer is a mystery to us. But despite of
scientific curiousity we should hope we will not have to stand such an event
again.