[meteorite-list] 'Meteor' drop-tests, have been done?

From: (wrong string) ørn Sørheim <bsoerhei_at_meteoritecentral.com>
Date: Thu Apr 22 10:22:39 2004
Message-ID: <200306162151.XAA16920_at_mail46.fg.online.no>

Pekka & List,

At 01:58 16.06.03 +0300, you wrote:
>Hello, Bjorn and the list,
>
>we had some speculations last winter in Finland to try some
>kind of dropping, but as far as I know, nobody here has tried...;-
>
>We tried to find information about this kind of test, but with
>no results. We consulted people from different universities in
>Europe, US and Canada, and there was not information available
>in this kind of tests in practise.

There are some scientists that do shoot small, mm-size, metal
balls ito ice surfaces and study the resulting craters.
They then use scaling laws to draw conclusions about the
really big craters on icy bodies.
Burchell and Grey at the University of Canterbury, England are
two of them.
But they are actually more interested in the crater form, not the
cracking pattern around it. A crater is hardly of interest in the
case of just the hole into a relative thin ice surface.
I think the _cracking patterns_ in such cases is the feature that will
tell the tale only.

I'm also interested in looking at practical results in the
nature, with different values of thickness of ice, temperatures,
angle, speed.

>Think this can be also quite simply calculated and simulated,
>but I´m not a mathematician...

Seems to be a bit removed from what you might see on a frozen lake
some winter day..
Especially taking into account how easy it would be to
do a drop-experiment.

>If you know the thickness and the structure of the ice, mass /
>size / angle of the falling specimen, this should not be a problem for a
>professional. It also should be remembered, if you make this
>kind of test somewhere, it´s only valid in exactly same circumstances.
>
>Usually the meteoroids don´t have any cosmic velocity left, when
>they drop, so they come down in free fall. The quite simple test is
>try to shoot a hole in the ice. Let´s say, you use 9.00 mm bullet and
>check the exact angle and the distance from the ice, when shoot, so
>the energy of the hit can be exactly calculated. More problematic case
>is the structure of the ice. If we are talking about steel-ice in the
>middle
>of the winter, let´s say, 60 cm:s thick, I bet, the hole you can get, it´s
>not deeper than 15 cm:s. The case is different in spring-time, when the
>ice with same 60 cm:s thickness is usually layered at least in 2 parts,
>strong steel-ice on the bottom, and week ice containing lot of water on
>the top. But anyway, think some modelling can be made. This may be
>a bit safer way than drop the stones from the plane.
>
>Anyway, if you are going to make this test, please, let me know the results,
>and also the dropping-area, so I know to wear a safety-helmet if happen to
>be near...;-

Well, I'm probably not trying in the summer-time, even though there
are lakes in the mountains here that are covered in ice at this time.
But they probably do not have the sought after type of ice.

Anyway, I'm still surprised that no one seems to have done such tests
previously...

God sumar!,
Bjørn Sørheim

>
>Bjørn Sørheim wrote:
>
>>At 21:37 14.06.03 GMT, you wrote:
>>
>>>Hello List,
>>>
>>>For my part, living in a country with a tremendous number of
>>>ice-covered lakes in the winter time (a really LARGE area) dropping
>>>such objects on _ice lakes_ would be of even more interest.
>>>
>>
>>Just to avoid confusion:
>>I'm simply talking about a frozen, that is
>>a lake covered with ice - I bet you have seen it :-)
>>
>>
>>>Such a drop mark would surely have its very distinct kind of features,
>>>very different from other causes of marks. I have personally found no
>>>references to science on such features anywhere up to now...
>>>
>>
>>>Surely it must have been done, yes..? Any references?
>>>
>>
>>Best wishes,
>>Bjørn Sørheim
>>
>>
>>
Received on Mon 16 Jun 2003 05:51:40 PM PDT