June 30, 1908: A Very Close Encounter of the Second Kind: "
1908: A fireball streaking across the sky and a massive explosion in the Siberian hinterlands marks the largest recorded collision ever between Earth and an object from space.
The Tunguska event flattened 80 million trees covering 830 square miles of sparsely populated (but not unpopulated) Russian outback in the region of the Tunguska River northwest of Lake Baikal.
Whatever it was -- an exploding fragment from a disintegrating meteorite seems the likeliest explanation -- scientists concluded there was no actual impact. The explosion appears to have been caused by an air burst similar to that of an artillery round detonating in midair, rather than on impact with the ground. In this case, the fragment, which is believed to have measured perhaps 100 feet across (although new research suggests it may have been even smaller), was probably traveling at around 21,000 miles per hour when it exploded anywhere from four to six miles above the Earth's surface.
Based on later assessments of the damage, the force of the blast was estimated to be between 10 and 15 megatons of TNT, roughly a thousand times more powerful than the atomic bomb that destroyed Hiroshima.
The remoteness of the blast and the chaotic conditions prevailing inside Russia at the time prevented a thorough examination of the area until 1927, when an expedition from the Soviet Academy of Sciences finally arrived on the scene. Ironically, a lot of the data wouldn't be clearly understood until the Soviet Union began conducting its own Cold War experiments with atomic-blast impacts during the 1950s and '60s.
Soil samples revealed high levels of nickel and iridium, which are commonly found in meteorites, and the pattern of the forest devastation was consistent with a strong central detonation followed by shock waves emanating outward from ground zero.
Based on eyewitness accounts at Tunguska, a bluish fireball appeared in the sky at around 7:15 a.m. Ten minutes later, there was a flash, followed by a deafening explosion that was heard 300 miles away. The ground began shaking as in an earthquake, and a hot wind blew across the land, singeing crops and shattering windows.
While contemporary accounts refer to many people in the vicinity becoming covered with boils and dying as a result of the blast, that may be better explained by a smallpox epidemic that was occurring at the same time.
The fear, of course, is that the Earth is vulnerable to these meteor strikes. Flying objects enter the atmosphere every day, but the vast majority burn up before posing any real threat. Some meteorites do get through, however, and there have been events similar to -- if smaller than -- Tunguska recorded in the past century.
Here's something to consider: In its 1966 edition, the Guinness Book of Records concluded that, based on the Earth's rotation, had the Tunguska meteorite struck 4 hours, 47 minutes later, it would have obliterated St. Petersburg, then the capital of imperial Russia. Given the events that would shortly torment that nation -- and all of Europe -- for the better part of the 20th century, one is left to wonder how history might have changed in those circumstances.
Sounds like the premise for a pretty good alternative-history novel.
Source: Various
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