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Tunguska…The Mystery Continues July 17, 2009

Posted by sgoebel in Asteroid, Astronomy.
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Shannon Goebel has her blog at:    http://mrsgoebel.wordpress.com/

As the saying goes, everyone loves a good mystery and the 1908 Tunguska Event does not disappoint.  I have long been fascinated by this story and love to discuss it each year with my Earth Science students.  However, just as in my classroom before we can delve into the juicy details and “who-dun-it’s”, we must first explore the history surrounding this event.

When? Where?

It was a quiet morning around seven o’clock on June 30, 1908 (June 17, 1908 according to the Julian Calendar which was in local use at the time)  in remote Siberia near the Podkamennaya Tunguska River.  The day started just like any other; no one would have predicted that it would forever be recorded and remembered for the unique and literally Earth-shattering event that would take place.   One of the first questions that probably comes to your mind, is where exactly is this place?  Shown on the map below, the Tunguska River is located in what is known today as the Krasnoyarsk Krai in Russia.

Photo taken from www.science.nasa.gov

Photo taken from www.science.nasa.gov

What?

For this portion of our investigation, we should begin with the basics upon which most scientists currently agree.  According to Don Yeomans, manager of the Near-Earth Object Office at NASA’s Jet Propulsion Laboratory, “It is the only entry of a large meteoroid we have in the modern era with first-hand accounts.”  The impact is believed to have been caused by the air burst caused by a large space rock (the true identity of which will be discussed soon), at an altitude of 5-10 kilometers (or for those meterically challenged people, 3-6 miles) above the Earth’s surface.
One major factor in this mystery is that the first scientific expedition to the area did not take place until 19 years after the event. In 1921 the first expedition to the area led by Leonid Kulik, the chief curator for the meteorite collection of the St. Petersburg museumset out but was cut short to due to the extremely harsh conditions of the area.  However six years later, a second expedition, again lead by Kulik, reached its goal.
Photo taken by Professor Leonid Kulik on his 1927 expedition to the impact site.
Photo taken by Professor Leonid Kulik on his 1927 expedition to the impact site.

While on their investigation, the crew collected numerous eyewitness testimonies like the one given below by S. Semenov.

“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.”

But what exactly was this so-called “space rock”?  That is what scientists are still debating 100 years later!  Information given on NASA’s website states the following.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.”
However, a recent article published by Kelley, Seyler, and Larsen brings new light to this subject.  This group of researchers suggest that instead of meteorite being responsible for this impact, perhaps a comet is to blame.  Their hypothesis is based upon data collected from space shuttle launches that took place almost 100 years after the Tunguska Event.  “The research, accepted for publication (June 24, 2009) by the journal Geophysical Research Letters, published by the American Geophysical Union, connects the two events by what followed each about a day later: brilliant, night-visible clouds, or noctilucent clouds, that are made up of ice particles and only form at very high altitudes and in extremely cold temperatures.” (www.sciencedaily.com/releases/2009/06/090624152941.htm)
So, what is really to blame for this mysterious impact?  Well, I guess that I will leave that up to you and your research to decide!  Regardless of which side you choose, this is an amazing so far one of a kind event for us to study.  Perhaps what we learn can help prepare us for other Near Earth Objects that are headed our way in the future.  Happy hunting!
References & Useful Links for More Information:
http://science.nasa.gov/headlines/y2008/30jun_tunguska.htm
http://www.sciencedaily.com/releases/2008/07/080715103956.htm
http://www.sciencedaily.com/releases/2009/06/090624152941.htm
http://en.wikipedia.org/wiki/Tunguska_event
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