It's June 30, 1908, and it's just after seven in the morning. A man is sitting on the front porch of a trading post at Vanavara in Siberia. Little does he know, in a few moments, he will be hurled from his chair and the heat will be so intense he will feel as though his shirt is on fire. That's how the Tunguska event felt 40 miles from ground zero.
Today, June 30, 2016, is the 108th anniversary of that ferocious impact near the Podkamennaya Tunguska River in remote Siberia--and more than a century later, scientists are still talking about it. In fact, for the past few years, on the anniversary of this event, scientists worldwide are observing Asteroid Day today! The goal of the day, is increasing awareness about these giant rocks near Earth.
Trees downed by the Tunguska explosion. Credit: the Leonid Kulik Expedition
While the impact occurred in '08, the first scientific expedition to the area would have to wait for 19 years. In 1921, Leonid Kulik, the chief curator for the meteorite collection of the St. Petersburg museum led an expedition to Tunguska. But weather prevented his teams' attempt to reach the blast zone.
In 1927, a new expedition, again lead by Kulik, reached its goal. While testimonials may have at first been difficult to obtain, there was plenty of evidence lying around. Eight hundred square miles of remote forest had been ripped asunder.
Eighty million trees were on their sides, lying in a radial pattern.
Map of damage pattern through 500,000 acres of Siberian Forest near Tunguska Russia
"Those trees acted as markers, pointing directly away from the blast's epicenter," said Yeomans. "Later, when the team arrived at ground zero, they found the trees there standing upright – but their limbs and bark had been stripped away. They looked like a forest of telephone poles."
In order to rip branches off trees like this, it requires fast moving shock waves that break off a tree's branches before the branches can transfer the impact momentum to the tree's stem. Thirty seven years after the Tunguska blast, branchless trees would be found at the site of another massive explosion – Hiroshima, Japan.
Massive deforestation after Tunguska explosion.
Kulik's expeditions (he traveled to Tunguska on three separate occasions) did finally get some of the locals to talk. One was the man based at the Vanara trading post who witnessed the heat blast as he was launched from his chair. His account: Suddenly in the north sky… the sky was split in two, and high above the forest the whole northern part of the sky appeared covered with fire… At that moment there was a bang in the sky and a mighty crash… The crash was followed by a noise like stones falling from the sky, or of guns firing.
The earth trembled. The massive explosion packed a wallop. Dense clouds formed over the region at high altitudes which reflected sunlight from beyond the horizon. Night skies glowed, and reports came in that people who lived as far away as Asia could read newspapers outdoors as late as midnight.
Locally, hundreds of reindeer, the livelihood of local herders, were killed, but there was no direct evidence that any person perished in the blast.
There is still some debate about what happened there, "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."
Artistic rendition of 1908 Tunguska blast
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.
Yeomans and his colleagues at JPL's Near-Earth Object Office are tasked with plotting the orbits of present-day comets and asteroids that cross Earth's path, and could be potentially hazardous to our planet. Yeomans estimates that, on average, a Tunguska-sized asteroid will enter Earth's atmosphere once every 300 years.
In the past 3 years, 72 new near Earth-objects have been discovered. Of those, 8 are classified as potentially hazardous to our planet, and could approach or hit Earth one day. Right now, NASA's Near Earth-Object Program says there are no big asteroids at risk of of hitting Earth anytime soon. But let's take a moment to remember the damage caused by a small meteor back in February of 2013 in Russia. 1,000 people were injured in the blast.
This video below is a compilation of some of the best shots from that day.
Video Courtesy: Artur Alves
Text information provided by Dr. Tony Phillips of NASA
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