It Happened 101 Years Ago Today

Map of Russia showing the approximate location of the Tunguska (tune-GOOSE-kuh) Event. Credit: Wikimedia

Exactly 101 years ago today at 7:17 a.m. local time, a trail of light brighter than the sun followed by several enormous explosions, rocked the air over the Tunguska River in Siberia and scared the living daylights out of the local reindeer herders. The blast flattened trees over an 800 square mile area but strangely, left no meteorites or crater. Sensitive barometers as far away as England recorded the sudden change in atmospheric pressure from the blast wave, while for several days afterword the night sky across Europe and Asia was aglow with strange, bright clouds.

Not until 1921 did anyone attempt to find out what happened that day. That’s when Russian mineralogist Leonid Kulik (left) put together an expedition to trek to the site of the explosion. The incredibly remote and difficult terrain put the kabosh on his first attempt but his second, in 1927, was successful.

The pictures show it all. Over 80 million trees were flattened, and those near the epicenter were stripped of their bark and limbs. Debranching without destroying an entire tree requires a shock wave similar to that in a nuclear bomb. Kulik photographed the landscape and described what he saw but could find no trace of what caused the damage.

A swath of trees that were flattened in a radial or circular pattern by the blast wave from the comet or meteorite that exploded in the air over Siberia on June 30, 1908. Credit: Leonid Kulik expedition

Another view of the flattened trees taken by Kulik’s discovery party. If the aerial blast had occured over a large city, it’s estimated 500,000 people would have died. Credit: Leonid Kulik expedition

While no one is certain exactly what caused the Tunguska Event, the most likely explanation is that an asteroid or comet, traveling at over 30,000 mph, detonated and annhilated itself some five miles up in Earth’s atmosphere due to the incredible pressures and heat on entry. The aerial destruction released the equivalent of 185 Hiroshima atom bombs. This would explain the explosion effects as well as the lack of a crater or meteorites. Interestingly, later expeditions into the region turned up tiny spherules of meteoric material in the trees and soil, possibly the dusty debris from the explosion.

Recent research now points to a comet as the likely culprit rather than a small asteroid. Asteroids are rocky while comets are primarily made of ice. What tipped scientists off were those reports of glowing clouds late at night. They are almost certainly noctilucent (noc-ti-LOO-sent) or "night shining" clouds, located 55 miles high in the atmosphere, far above most familiar weather clouds. They’re visible from the northern U.S., Canada and Europe, and appear very low in the northern sky near the end of evening or the beginning of morning twilight when all other clouds are dark.

Michael Kelley, the James A. Friend Family Distinguished Professor of Engineering at Cornell, who led the research team, compared the space shuttle’s exhaust plume to the water vapor that would be released by a comet striking the atmosphere. Kelley saw noctilucent clouds created by the shuttle flights in 1997, 2003 and 2007. A comet would have broken up at the same height as the water exhaust.

"It’s almost like putting together a 100-year-old murder mystery," said Kelley. "The evidence is pretty strong that the Earth was hit by a comet in 1908." To read more about the team’s research, click here.

I wish I’d been in a better location when I took this photo of noctilucent clouds last Friday morning. Too many trees! The display was extremely low in the northern sky around 3:15 a.m. Details: 200mm lens at f/2.8, 15 second time exposure at ISO 800. Photo: Bob King

Just the other morning I was out admiring Venus and Mars when I saw my first noctilucent clouds of the summer. They were very low in the northern sky around 3:15 a.m. some two hours before sunrise. Long summer twilights are the best time to watch for these elusive beauties. Look for delicate white tendrils stretching very low across the north when the stars begin to appear. Binoculars will help bring out the clouds’ intricate detail. Whether what you’re seeing is spent shuttle exhaust or a remnant of Tunguska, there’s magic in these strange clouds.