🚀 go-pugleaf

In article <Bx3CM5.7Gx.1@cs.cmu.edu> amon@elegabalus.cs.qub.ac.uk writes:
{Actually, I (jscotti@lpl.arizona.edu) wrote this:}
>> Not really screwy.  The number of 50 meter objects is enhanced by
>> about 10 times and the Tunguska type events probably happen once
>> or a few times per century.  Remember, 3 out of 4 enter over water
>> and may be less likely to be detected.  Also, perhaps a large
>> 
>
>
>I wonder... Could this be the explanation for the non-radioactive  
>mushroom cloud seen by airline pilots in the Pacific one day in the  
>late 70's - early 80's? It was never connected to any source that I  
>am aware of.

I vaguely remember hearing something about this.  The rate of small
asteroid impact could very well account for such an event.  I doubt
we can conclusively identify it as an asteroid impact, but the
probability of such an event happening is quite high.

>Some theorized it was caused by an undersea volcanic explosion, but  
>no one succeeded in associating it with one. It was not a nuclear  
>explosion, although some at first suggested that. It is unlikely to  
>have been a non-nuclear explosion, ie no ships disappeared and I'm  
>not sure I see a motive for an experimental blast in that part of the  
>world. 

In the absence of further evidence, we'll just have to add small 
asteroid impacts as a possibility.

>Just a thought, although I would not expect a mushroom cloud from  
>such a comet strike. I'm not sure I can even see a mechanism for  
>creating one from a Tunguska class strike.

The mechanism is quite understandable.  You have an object moving
at hypersonic velocity as it enters the atmosphere.  A stony or
stony iron object could easily survive into the low atmosphere where
the aerodynamical stress catastrophically ruptures it and it explodes
just like a bomb.  The estimated impact energies of 10-100 meter
objects traveling at typical velocities is measured in the kilotons
on the small end to 10s of megatons on the large end and that kinetic
energy has to go somewhere!  Smaller objects fracture high in the
atmosphere and appear as bright bolides which leave trails and 
fragments along the way.  If the object is strong enough, it might
survive largely intact with most of its kinetic energy and might
create an impact crater such as was made about 50,000 years ago when
the Diablo Canyon Meteor crater was formed in Arizona.  That crater
is thought to have been formed by the impact of a stony iron object
only about 30 meters in diameter.  Objects strong enough to survive
atmospheric entry are fortunately rare.

By the way, the Tuguska event was observed by residents of the 
region and their description of the explosion matchs that of a nuclear
bomb blast quite closely.

Jim.
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Jim Scotti 
{jscotti@lpl.arizona.edu}
Lunar & Planetary Laboratory
University of Arizona
Tucson, AZ 85721 USA
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