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Re: Cometary meteoroids landing on sea?

Hello,

The reason for my interest in surviving cometary meteoroids 
was of course that I had an observation of credible witnesses
that defied all other explanations. Therefore I tried this 'model'
of comertary material which could float and maybe even glow at
sea afterwards.

I myself have previously also believed that cometary material would 
be much more fragile than stones (and iron) to survive the entry 
through earth's atmosphere. 

But I now realize that that this has been under an unconscious 
misconception that this material would have earthly teperatures -
around 0 deg. (Celsius). 
This is of course NOT the case. The comets with smaller fragments
generally enter the inner parts of the solar system from the Oort cloud -
as long as they are short periodic, where the temperatures are close
to absolute zero (-273 deg. C). And even if the fragments were
shortperiodic, they would come from an asteroid distance 
(3 AU and beyond) and we know that the temperature there are 
-100 deg. Celsius and downwards.
I don't know what the fraction between long and shortperiodic fragments
would be, but I guess the former is most prominent.
That means that on average cometary fragment is - as erlier mentioned -
hard as _stone or metal_.

You might say that even if the frozen ices are stone hard, the melting
point is much lower and the crystal structure is weaker, so it still
would not survive.

Well as long as I don't have quantitative numbers showing the exact
'weakness level' compared to stones I cannot refute the possibility that
cometray fragments survives (at least some of the time). If someone
can supply such numbers (whatever they show) I would appreciate it 
very much.

Adding to the unsurety are the great variety of the entry-parameters.
Foremost the entry velocity (a result of velocity in its orbit and
the direction where it hits the earth - head on or from behind).
The 'object' this all started with, ondoubtedly came from behind,
(about 40 deg. to the side it seems). So therefore it would be of
the slower objects, greatly boosting its survival possibility.
Also the height angle. This 'object' was coming more or less
straight down, again boosting its possibilities.

Also there must be differences between the material in comets.
Some have more of compounds making it stronger - more
like stony material. Again making such fragments more likely
to survive. 
Some fragment may also have a shape (areodynamic) that is helping
it in its survival. ('The survival of the fittest'!)

Like others have posted, it's also hard to understand how some
of the more friable chondrites (like Bjurbole, Saratov etc.)
and carbonaceous chondrites could have survived.
If these stones survived, it's very hard to believe that some 
cometray fragments could not also survive.
Also meteorites travelling faster than 26 miles pr. sec have
been known to survive in spite of having a kinetic energy more 
than 10 times that of the slowest, but still they have made it 
to the ground.

As again 38% of the brighter fireballs are cometary one might ask:
Do you meam to say that all these fireball, without regard to size,
temperature, composition, speed, direction or structure burn up/
explode in the atmosphere and not a single one have come to the ground
through the millions of years. 
At what heights do they decay, and what are the minimum height 
they do decay - according to you? Again numbers would be appreciated.

I would imagine that the reason that cometary fragments have 
been believed  not to reach the surface is:

- If hit a firm surface it would easier explode and turn to dust.
- If it was not found very soon it would have melted and would be 
  gone forever.
- if it landed in snow it would not be noticed
- If it landed in the sea it would not be noticed, at least not in
  the northern hemisphere, and in the temperate region it would 
  have melted very quickly.
- In recent times, ice from above is solely believed to come from 
  aeroplanes.

Regards,
Bjørn Sørheim


At 16:41 11.07.98 EDT, you wrote:
>In a message dated 98-07-11 13:25:12 EDT, you write:
>
>bjorn<< The ice block will be much
> more affected by air resistance. <<
>
>Yes it would...When it encounters the dense atmosphere...before terminal
>velocity occurs, it would be like throwing a dirt cloud real hard against a
>concrete wall. It will splatter.


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