Wednesday, June 27, 2007

An explosion of interest

99 years ago this Saturday, on June 30, 1908, some widely scattered residents near the Tunguska River of Siberia reported seeing and/or hearing a series of flashes and booms. Seismographs across Europe detected a magnitude 5.0 earthquake in Siberia. Atmospheric pressure gauges in Britain picked up a series of pressure disturbances, and the night skies glowed for several days.

Not until 1921 did anybody discover more about what happened. An expedition to the area found a region nearly 30 miles across with trees that were scorched and knocked over, each tree pointing toward the center of that region. But otherwise the region appeared unscathed. What happened?

Many ideas have been proposed as to the cause of the "Tunguska Event," including some very wild ideas (including UFO crashes and "mad scientist" Nikola Tesla's Death Ray), but over time the vast majority of scientists have come to believe that the Tunguska Event was either a small asteroid or comet that exploded at around 30,000 feet above the Siberian forest. The force of the explosion was about 15 megatons of TNT, or a thousand times the power of the atomic bomb dropped on Hiroshima in World War II. Yet other than some dusty particles that seem to come from outer space, no trace of the meteor has been discovered.

This may change by the 100th anniversary of the event. An Italian research team has announced that they suspect a lake near the center of the damaged trees to be a crater formed by a large piece of the original meteor. This lake has been explored before, but seemed to be old due to the amount of mud at its bottom. The problem is, there are no good maps of the region from before the Tunguska Event, so we don't really know if the lake is new or old.

The Italian team of researchers claims to find that the shape of the lake bed and jumbled rock underneath it are strong evidence that the lake is really the missing crater, and they intend to go back to search for any meteorites that may be at the bottom of the lake.

It is not necessarily surprising that we haven't found any trace of the asteroid or comet. If it exploded 5 miles in the air with a force of 15 megatons, most if not all of the body could have vaporized in the extreme heat. Also, we now know that many comets and asteroids are more like piles of rubble than solid rocks, so the meteor may have shattered into component pieces. Since 14 years passed between the Tunguska Event and the first expedition, the surviving fragments may have been buried or disguised as normal rocks by being exposed to wind, rain, snow, and other weather.

Finding a piece of the original meteor would be really important. We could learn, for example, if the meteor was from an asteroid or a comet. We could also lay to rest (for the umpteenth time) many of the wild theories of the Tunguska event. And, perhaps most importantly, we can learn what happens when medium- and large-sized rocks hit the Earth, gaining some valuable data that might help protect the Earth should we ever find another meteor on the way.

Time will tell if the lake that so interests the Italians will have more secrets to reveal, or if the encounter between the Earth and a chunk of rock or ice over Siberia in the summer of 1908 will remain a mysterious event.

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