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Re: (meteorobs) Tunguska bolide & Beta taurid stream



Just some thoughts about some arguments:
>POINTS IN FAVOUR OF A METEORITIC ORIGIN (Sekanina)
>1) The majority of evidence points to only one explosion - so no 
>fragmentation earlier in its flight.

Should a piece of cometary material necessarily break up during its flight through the atmosphere? I'm not sure if this is the best example, but Leonids and Perseids are of cometary origin and I haven't seen any break up, they often end with a terminal explosion though. 

>4) A fragment of cometary material could not have survived a plunge into the 
>lower atmosphere.
>
>5) The resistance of the air at a height of a 8.5 km is 1000 times as strong 
>as is necessary for the destruction of a comet entering the atmosphere at a 
>speed of 26 km/s which is normal for comets.

Do we really know enough about cometary nuclei and what they are composed of, or should we wait for Stardust, Rossetta and other missions? How much do we know about comets? (I'm not tryng to indicate a lack of knowledge, just a simple question)

> 7) Favorable position of the Tunguska object in the evening sky for several 
> weeks before the encounter- a comet should have been discovered.

From what I've read, the generally accepted diameter of a cometary Tunguska body is between 100 and 200 meters. If a nucleus of this size was active, the coma diameter would probably be small and the surface brightness low. I don't know if I can link this to the recen comet C/1998 K5 LINEAR, which was very near the Earth at the time of discovery ( 0.3 A.U.) but was faint, around +14.5 magnitude (a question, was this a mini-comet or a very unactive nucleus?). LINEAR was probably much larger than Tunguska body, so the latter would have been even fainter. In 1908 probably noone would be able to pick it up, unless by chance someone saw it with the largest telescopes, which were preoccupied with other projects.

> 8) Statistics of observed comets seem to indicate that there are no active 
> objects with nuclear diameters as small as a hundred meters.

The Tunguska body needn't be an active nucleus. Supposed it was only a fragment of comet Encke that broke off a while ago. Have we ever observed such a body? If it was not active, how could we distingush it from other NEO's? Is it possible that some NEO's are of such nature?

Clear skies!

Jure 
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