March 2, 2009 Asteroid 2009 DD45 a Near Miss
A small asteroid, designated 2009 DD45, passed the
Earth at a distance of 46,000 miles, a near miss in terms of
cosmic distances. Though asteroid 2009 DD45 was just about two
hundred feet long, it might have impacted with the force of a
nuclear blast. Astronomers are comparing asteroid 2009 DD45 to the
rock that caused the Tunguska impact of 1908. The 1908 impact
occurred in Siberia near the Tunguska River and destroyed the
taiga forest at a distance of twenty five kilometers around the
epicenter. The Tunguska impact, which was technically an air burst
explosion rather than a ground collision, had the force of a
multi-megaton nuclear blast. Had asteroid 2009 DD45 hit a
populated area, such as a large city, it would have laid it waste.
Had asteroid 2009 DD45 hit the ocean it would have caused a
tsunami that would have devastated coastlines. Astronomers suggest
that asteroid 2009 DD45 is now in a solar orbit that intersects
the Earth's orbit. That means that asteroid 2009 DD45 will be
visiting the vicinity of Earth again. The near miss of 2009 DD45,
which was detected just two or so days before it passed the Earth,
illustrates the continuing danger that the Earth faces due to
asteroid impacts. Asteroid 2009 DD45 suggests that not only
greater efforts should be made to detect and track such asteroids
before they become a threat, but strategies should be put into
place to divert them should they be found to be on a collision
course. An asteroid 2.5 to 6 miles in length impacted the Earth
near the Yucatan 65 million years ago. The Yucatan impact threw up
unimaginable amounts of water vapor, dust, and other debris,
blotting out the sun for years. It is thought to have rendered
most life on Earth, including the dinosaurs, extinct. A similar
impact in current times would certainly end human civilization and
likely the human species. The idea of an asteroid hitting the
Earth has been popularized in fiction and in cinema, including the
1998 films Armageddon and Deep Impact. Another film along those
lines, When Worlds Collide, a remake of a 1950s film based on a
1933 novel, is under development.
The Tunguska explosion occurred on the morning of June 30, 1908
at 7:17 A.M. local time (0h 17m 11s U.T.) in the area of the Stony
Tunguska River with the coordinates of the epicenter being 60º55’
N, 101º57’ E (Kridec 1966).
At around 7:15 a.m., Tungus natives and Russian settlers in the
hills northwest of Lake Baikal observed a column of bluish light,
nearly as bright as the Sun, moving across the sky. About 10
minutes later, there was a flash and a loud "knocking" sound
similar to artillery fire that went in short bursts spaced
increasingly wider apart. Eyewitnesses closer to the explosion
reported the sound source moving during each barrage, east to
north. The sounds were accompanied by a shock wave that knocked
people off their feet and broke windows hundreds of miles away.
The majority of eyewitnesses reported only the sounds and the
tremors, and not the sighting of the explosion. Eyewitness
accounts differ as to the sequence of events and their overall
The location of the Tunguska impact: 101º57'E, 60º55'N
Trees felled by the Tunguska explosion. Credit: the Leonid Kulik Expedition. [SOURCE]
The explosion registered on seismic stations across Eurasia.
Although the Richter scale was not developed until 1935, it has
been estimated that in some places the shock wave would have been
equivalent to an earthquake of 5.0 on the Richter scale. It also
produced fluctuations in atmospheric pressure strong enough to be
detected by then recently invented barographs in Britain. Over the
next few weeks, night skies were aglow such that one could read in
their light, sometimes called "bright nights." In the United
States, the Smithsonian Astrophysical Observatory and the Mount
Wilson Observatory observed a decrease in atmospheric transparency
that lasted for several months.
FIG 1. Area map of the 1908 Tunguska explosion event. After Sullivan 1979.
The Guinness Book of World Records (1966 edition) states that
due to the rotation of the Earth, if the collision had occurred 4
hours 47 minutes later, it would have completely destroyed the
city of St. Petersburg.
There was little scientific curiosity about the impact at the
time, possibly owing to the isolation of the Tunguska region. If
there were any early expeditions to the site, the records were
lost during the subsequent chaotic years - World War I, the
Russian Revolution of 1917, and the Russian Civil War.
The first recorded expedition arrived at the scene more than a
decade after the event. In 1921, the Russian mineralogist Leonid
Kulik, visiting the Podkamennaya Tunguska River basin as part of a
survey for the Soviet Academy of Sciences, deduced from local
accounts that the explosion had been caused by a giant meteorite
impact. He persuaded the Soviet government to fund an expedition
to the Tunguska region, based on the prospect of meteoritic iron
that could be salvaged to aid Soviet industry.
Kulik's party reached the site in 1927. To their surprise, no
crater was to be found. There was instead a region of scorched
trees about 50 kilometres (30 mi) across. A few near ground zero
were still strangely standing upright, their branches and bark
stripped off. Those farther away had been knocked down in a
direction away from the center.
FIG 2. Map depicting fallen tree pattern (arrows represent direction) from
explosion of 1908. This is a closeup of the impact site of Figure 1. After
Sullivan 1979 and Kridec 1966.
Trees near the Podkamennaya Tunguska River in
Siberia still looked devastated nearly two decades after a large
meteorite exploded above the ground in June 1908. The Tunguska
event, which ranks as one of the most violent cosmic impacts of
this century, leveled nearly 800 square miles of forested taiga.
The curious effect of the Tunguska explosion on the trees near
ground zero was replicated during atmospheric nuclear tests in the
1950s and 1960s. These effects are caused by the shock wave
produced by large explosions. The trees directly below the
explosion are stripped as the blast wave moves vertically
downward, while trees further away are felled because the blast
wave is travelling closer to the horizontal when it reaches them.
Soviet experiments performed in the mid-1960s, with model
forests (made of matches) and small explosive charges slid
downward on wires, produced butterfly-shaped blast patterns
strikingly similar to the pattern found at the Tunguska site. The
experiments suggested that the object had approached at an angle
of roughly 30 degrees from the ground and 115 degrees from north
and had exploded in mid-air.
During the next ten years there were three more expeditions to
the area. Kulik found a little "pothole" bog that he thought might
be the crater, but after a laborious exercise in draining the bog,
he found there were old stumps on the bottom, ruling out the
possibility that it was a crater. In 1938, Kulik managed to
arrange for an aerial photographic survey of the area, which
revealed that the event had knocked over trees in a huge
butterfly-shaped pattern. Despite the large amount of devastation,
there was no crater to be seen. Expeditions sent to the area in
the 1950s and 1960s found microscopic glass spheres in siftings of
the soil. Chemical analysis showed that the spheres contained high
proportions of nickel and iridium, which are found in high
concentrations in meteorites, hinting that they were of
Detailed systematic eyewitness reports began to be gathered as
late as 1959, when interviews were conducted with many of the
indigenous people who had been within 100 kilometres (60 mi) of
the explosion. Most of these accounts claimed that the local
people had been covered with boils after the explosion, with whole
families dying off. The medical scientists attached to the
expedition concluded that there had been an epidemic of smallpox
in the area at the time. Expeditions led by Gennady Plekhanov
found no elevated levels of radiation, which would have been
expected had the detonation been nuclear in nature.
"At breakfast time I was sitting by the house at Vanavara
trading post (65 kilometres/40 miles south of the explosion),
facing North. [...] I suddenly saw that directly to the North,
over Onkoul's Tunguska road, the sky split in two and fire
appeared high and wide over the forest (as Semenov showed, about
50 degrees up - expedition note). The split in the sky grew
larger, and the entire Northern side was covered with fire. At
that moment I became so hot that I couldn't bear it, as if my
shirt was on fire; from the northern side, where the fire was,
came strong heat. I wanted to tear off my shirt and throw it
down, but then the sky shut closed, and a strong thump sounded,
and I was thrown a few yards. I lost my senses for a moment, but
then my wife ran out and led me to the house. After that such
noise came, as if rocks were falling or cannons were firing, the
earth shook, and when I was on the ground, I pressed my head
down, fearing rocks would smash it. When the sky opened up, hot
wind raced between the houses, like from cannons, which left
traces in the ground like pathways, and it damaged some crops.
Later we saw that many windows were shattered, and in the barn a
part of the iron lock snapped."
-- Testimony of S. Semenov, as recorded by Leonid
Kulik's expedition in 1930.
"We had a hut by the river with my brother Chekaren. We
were sleeping. Suddenly we both woke up at the same time.
Somebody shoved us. We heard whistling and felt strong wind.
Chekaren said, 'Can you hear all those birds flying overhead?'
We were both in the hut, couldn't see what was going on outside.
Suddenly, I got shoved again, this time so hard I fell into the
fire. I got scared. Chekaren got scared too. We started crying
out for father, mother, brother, but no one answered. There was
noise beyond the hut, we could hear trees falling down. Me and
Chekaren got out of our sleeping bags and wanted to run out, but
then the thunder struck. This was the first thunder. The Earth
began to move and rock, wind hit our hut and knocked it over. My
body was pushed down by sticks, but my head was in the clear.
Then I saw a wonder: trees were falling, the branches were on
fire, it became mighty bright, how can I say this, as if there
was a second sun, my eyes were hurting, I even closed them. It
was like what the Russians call lightning. And immediately there
was a loud thunderclap. This was the second thunder. The morning
was sunny, there were no clouds, our Sun was shining brightly as
usual, and suddenly there came a second one!
"Me and Chekaren had some difficulty getting under from the
remains of our hut. Then we saw that above, but in a different
place, there was another flash, and loud thunder came. This was
the third thunder strike. Wind came again, knocked us off our
feet, struck against the fallen trees.
"We looked at the fallen trees, watched the tree tops get
snapped off, watched the fires. Suddenly Chekaren yelled 'Look
up' and pointed with his hand. I looked there and saw another
flash, and it made another thunder. But the noise was less than
before. This was the fourth strike, like normal thunder.
"Now I remember well there was also one more thunder strike, but
it was small, and somewhere far away, where the Sun goes to
-- Testimony of Chuchan of Shanyagir tribe,
as recorded by I.M.Suslov in 1926.
"On the 17th of June, around 9 in the AM, we observed an
unusual natural occurrence. In the N Karelinski village (200
verst N of Kirensk) the peasants saw to the North-West, rather
high above the horizon, some strangely bright (impossible to
look at) bluish-white heavenly body, which for 10 minutes moved
downwards. The body appeared as a "pipe", i.e. a cylinder. The
sky was cloudless, only a small dark cloud was observed in the
general direction of the bright body. It was hot and dry. As the
body neared the ground (forest), the bright body seemed to
smudge, and then turned into a giant billow of black smoke, and
a loud knocking (not thunder) was heard, as if large stones were
falling, or artillery was fired. All buildings shook. At the
same time the cloud began emitting flames of uncertain shapes.
All villagers were stricken with panic and took to the streets,
women cried, thinking it was the end of the world. "The author
of these lines was meantime in the forest about 6 verst N of
Kirensk, and heard to the NE some kind of artillery barrage,
that repeated in intervals of 15 minutes at least 10 times. In
Kirensk in a few buildings in the walls facing north-east window
-- Sibir newspaper, July 2, 1908
"When the meteorite fell, strong tremors in the ground
were observed, and near the Lovat village of the Kansk uezd two
strong explosions were heard, as if from large-caliber
-- Siberian Life newspaper, July 27, 1908
"Kezhemskoe village. On the 17th an unusual atmospheric
event was observed. At 7:43 the noise akin to a strong wind was
heard. Immediately afterwards a horrific thump sounded, followed
by an earthquake which literally shook the buildings, as if they
were hit by a large log or a heavy rock. The first thump was
followed by a second, and then a third. Then - the interval
between the first and the third thumps were accompanied by an
unusual underground rattle, similar to a railway upon which
dozens of trains are traveling at the same time. Afterwards for
5 to 6 minutes an exact likeness of artillery fire was heard: 50
to 60 salvoes in short, equal intervals, which got progressively
weaker. After 1.5 - 2 minutes after one of the "barrages" six
more thumps were heard, like cannon firing, but individual,
loud, and accompanied by tremors. "The sky, at the first sight,
appeared to be clear. There was no wind and no clouds. However
upon closer inspection to the North, i.e. where most of the
thumps were heard, a kind of an ashen cloud was seen near the
horizon which kept getting smaller and more transparent, and
possibly by around 2-3 p.m. completely disappeared."
-- Krasnoyaretz newspaper, July 13, 1908
Below is our interpretation of satellite Images (Google Earth)
of the Impact area.
Tunguska the epicenter area: 60º55’ N, 101º57’ E
Coutesy of Google Earth. Click to enlarge image
Tunguska epicenter area. Click to enlarge image
Tunguska epicenter area. Click to enlarge image
Tunguska Explosion Theories
There were many theories proposed to explain Tunguska event (
exploding UFO, Black Hole, Antimatter, natural H-bomb), but the
generally agreed upon theory is that on the morning of June 30,
1908, a large space rock, about 120 feet across, entered the
atmosphere of Siberia and then detonated in the sky."
It is estimated the asteroid entered Earth's atmosphere
traveling at a speed of about 33,500 miles per hour. During its
quick plunge, the 220-million-pound space rock heated the air
surrounding it to 44,500 degrees Fahrenheit. At 7:17 a.m. (local
Siberia time), at a height of about 28,000 feet, the combination
of pressure and heat caused the asteroid to fragment and
annihilate itself, producing a fireball and releasing energy
equivalent to about 185 Hiroshima bombs.
Another estimate is that the explosion was most likely caused
by the airburst of a large (around 20 m (66 ft) across) meteoroid
or comet fragment at an altitude of 5 to 10 kilometers (3-6 mi)
above the Earth's surface. Although the meteor or comet is
considered to have burst prior to hitting the surface, this event
is still referred to as an impact event. The energy of the blast
was estimated to be between 10 and 20 megatons of TNT, 1,000 times
more powerful than the bomb dropped on Hiroshima, or equivalent to
Castle Bravo, the most powerful nuclear bomb ever detonated by the
The Tunguska explosion felled an estimated 80 million trees
over 2,150 square kilometers (830 sq mi). An overhead satellite
view, from nearly a century later, centered at 101º57'E, 60º55'N
(near ground zero for this event) shows an area of reduced forest
density with a clearly visible, irregular clearing of somewhat
less than one square kilometer in area. It is estimated to have
measured 5.0 on the Richter scale.
The Tunguska event is the largest impact event in recent
history. An explosion of this magnitude had the potential to
devastate large metropolitan areas should it occur over a large
city. This has helped spark discussion of ways to potentially stop
large asteroids or comets from hitting Earth.
Asteroid or Comet?
The composition of the Tunguska body remains a matter of
In 1930, the British astronomer F.J.W. Whipple suggested that
the Tunguska body was a small comet. A cometary meteorite, being
composed primarily of ice and dust, could have been completely
vaporized by the impact with the Earth's atmosphere, leaving no
obvious traces. The comet hypothesis was further supported by the
glowing skies (or "skyglows" or "bright nights") observed across
Europe for several evenings after the impact, apparently caused by
dust that had been dispersed across the upper atmosphere.
In 1978, Slovak astronomer Lubor Kresak suggested that the body
was a piece of the short-period Comet Encke, which is responsible
for the Beta Taurid meteor shower; the Tunguska event coincided
with a peak in that shower. It is now known that bodies of this
kind explode at frequent intervals tens to hundreds of kilometres
above the ground. Military satellites have been observing these
explosions for decades.
In 1983, astronomer Zdenek Sekanina published a paper
criticizing the comet hypothesis. He pointed out that a body
composed of cometary material, travelling through the atmosphere
along such a shallow trajectory, ought to have disintegrated,
whereas the Tunguska body apparently remained intact into the
lower atmosphere. Sekanina argued that the evidence pointed to a
dense, rocky object, probably of asteroidal origin.
This hypothesis was further boosted in 2001, when Farinella,
Foschini, et al. released a study suggesting that the object had
arrived from the direction of the asteroid belt.
Proponents of the comet hypothesis have suggested that the
object was an extinct comet with a stony mantle that allowed it to
penetrate the atmosphere.
The chief difficulty in the asteroid hypothesis is that a stony
object should have produced a large crater where it struck the
ground, but no such crater has been found. It has been
hypothesized that the passage of the asteroid through the
atmosphere caused pressures and temperatures to build up to a
point where the asteroid abruptly disintegrated in a huge
explosion. The destruction would have to have been so complete
that no remnants of substantial size survived, and the material
scattered into the upper atmosphere during the explosion would
have caused the skyglows.
Models published in 1993 suggested that the stony body would
have been about 60 metres across, with physical properties
somewhere between an ordinary chondrite and a carbonaceous
Christopher Chyba and others have proposed a process whereby a
stony meteorite could have exhibited the behavior of the Tunguska
impactor. Their models show that when the forces opposing a body's
descent become greater than the cohesive force holding it
together, it blows apart, releasing nearly all its energy at once.
The result is no crater, and damage distributed over a fairly wide
radius, all of the damage being blast and thermal.
High levels of carbon that doesn't form on Earth found in peat
bogs suggest a comet, which have high amounts of carbon compared
to most asteroids, was the cause of the Tunguska event; however,
it is not impossible for asteroids to contain the carbon necessary
to result in the heightened levels of carbon in the peat bogs in
During the 1990s, Italian researchers extracted resin from the
core of the trees in the area of impact, to examine trapped
particles that were present during the 1908 event. They found high
levels material commonly found in rocky asteroids and rarely found
Today, most Russian scientists believe the Tunguska event was
the result of a comet, while most American scientists take the
belief that it was some sort of asteroid.
The Tunguska explosion is indeed unique and mysterious. Of the
possible causes it appears that the present consensus favors the
comet hypothesis. However, suggesting a consensus is quite
tenuous. Though the other theories have plausibility, they have
difficulty explaining the observed event and the resulting
Making use of the cometary hypothesis allows for the following
Above central Siberia on June 30, 1908, at approximately 7:17
AM local time, a small comet entered the atmosphere from behind
the sun and moved in a southeast to northwest direction. The comet
was composed of about 30,000 tons of water, methane, and ammonia
ice with traces of silicates and iron oxides. Penetrating the
atmosphere at approximately 60 km/sec (130,000 mph), the object
created an intense shock wave which wrapped tightly around its
nose. As it descended that sunny morning, its nucleus exploded
(possibly 3 times) approximately 8 km above the Earth’s surface.
These three frames are from a
computer simulation of the 1908 Tunguska event.
An impactor with 5 megatons of kinetic energy disintegrates and
explodes 8 miles up,
sending a supersonic blast wave downward to the ground.
M. Boslough & D. Crawford / Sandia National Laboratories.
A huge black cloud immediately appeared following the explosion
which released 1023 ergs of energy. A heat wave with a temperature
of approximately 16.6 million degrees Celsius at the focus was
generated that had a tree-scorching effect for a radius of 15 km.
The heat wave was followed by air shock waves which disfigured or
toppled 80 million trees occupying approximately 8000 km2 of
Siberian taiga (a radius of 30 km), and initiated a seismic wave
of Richter magnitude 5, but, to our astonishment, left no crater.
The dust from the tail of the comet moved away from the sun and
provided anomalously bright night sky in Europe and parts of
Western Russia. No trace of the comet itself was found except for
tiny magnetite and silicate globules. The principal consequences
were fear and awe among the inhabitants of the region, and the
physical damage from the explosion. Fortunately, no human life was
lost, though more than a thousand reindeer were destroyed.
Speculation will continue as to the origin of this catastrophe,
yet no certain conclusions can be attained unless man has the
dubious opportunity to observe and monitor such an event in the
The Tunguska explosion directs our attention to catastrophic
forces which have helped form the earth, and causes us to ask
questions about the nature of much larger cosmic events.
What were the global effects of enormous impact events which
formed the 1-km-diameter Meteor Crater in Arizona (left image),
the 100-km-diameter Popigay crater of Siberia, and the
140-km-diameter Sudbury impact structure of Ontario? What changes
in the earth’s crust, atmosphere, ocean and life were caused by
the release of a million times more energy than the Tunguska
The Tunguska event provides a faint glimpse.
Subject Related Links and Resources
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