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Mystery still surrounds 1908 Tunguska event

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Author Topic: Mystery still surrounds 1908 Tunguska event  (Read 298 times)
Teri Charboneau
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« on: July 12, 2016, 01:54:46 am »

Artemieva now says there are clear stages that took place, which she has outlined in a review to be published in the Annual Review of Earth and Planetary Sciences in the second half of 2016.

    Most people think they come whaling in from outer space and leave a crater

First, the cosmic body entered our atmosphere at 9-19 miles per second (15-30km/s).

Fortunately, our atmosphere is good at protecting us. "It will break apart a rock smaller than a football field across," explains NASA researcher Bill Cooke, who leads NASA's Meteoroid Environment Office. "Most people think they come whaling in from outer space and leave a crater, and there's a big smoking piece of rock on the ground. The truth is kind of the opposite."

The atmosphere will generally break rocks up a few kilometres above the Earth's surface, producing an occasional shower of smaller rocks that, by the time they hit the ground, will be cold.

In the case of Tunguska, the incoming meteor must have been extremely fragile, or the explosion so intense, it obliterated all its remnants 8-10km above Earth.

This process explains the event's second stage. The atmosphere vaporised the object into tiny pieces, while at the same time intense kinetic energy also transformed them into heat.

"The process is similar to a chemical explosion. In conventional explosions, chemical or nuclear energy is transformed into heat," says Artemieva. 

    The intense heat resulted in shockwaves that were felt for hundreds of kilometres

In other words, any remnants from whatever entered Earth's atmosphere were turned into cosmic dust in the process.

If events unfolded this way, it explains the lack of large chunks of cosmic material at the site. "It is very difficult to find a millimetre-size grain in a big area. It is necessary to search in the peat," says Kvasnytsya.

As the object entered our atmosphere and broke apart, the intense heat resulted in shockwaves that were felt for hundreds of kilometres. When this airburst then hit the ground it flattened all the trees in the vicinity.
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