[meteorite-list] Friable meteorites

From: MexicoDoug <mexicodoug_at_meteoritecentral.com>
Date: Mon, 24 Oct 2011 02:02:58 -0400 (EDT)
Message-ID: <8CE6029B6646631-D54-52660_at_Webmail-m105.sysops.aol.com>

Pete wrote:

"My question is how do they survive to the ground, to be found not as a
dust, but in large pieces?"

Pete you're in the good company of David Rittenhouse who asked the same
question in 1780.

It's related to the other conundrum - How do they stay relatively cool
inside while the surface becomes fused? That seemingly goes against
common sense. And with Irons it is even better because at much lower
temperatures, the Widmanstatten pattern would become annealled and
lost. Yet there is a fusion region on irons that can be measured in
fractions of a millimeter in some cases, and never much more.

Somehow, and I'm winging it though I should know, the process of
ablation is so darn efficient at removing the heat generated, much like
we sweat, that the ablating surface provides a natural air conditioner
for what's inside, just like a swamp cooler but absorbing even by an
electric excitation mechanism which discharges the energy by
transforming from electrical into light energy, hece the brightness
observed/

But that still doesn't explain why going into a headwind of 10 miles
per second everything doesn't rip apart. That must, and please correct
me if I am wrong, be due to two or three factors working in concert on
the forward face of the mass:
1. heat is wicked off immediately by the sublimation described above
2,3. the ablated material leaving the surface creates a plasma which
either has a much lower frictional coefficient or creates a static
layer of plasma travelling with the object which essential operates as
a battering ram forming its own sacrificial layer, or both.

Thus, the rock from space is like an insulated kernal traveling in its
own form in place shields.

When it finishes its high energy velocities it goes into free fall
which reaches a maximum speed of under 400 mph in most cases much less
which upon hitting a soft surface can survive. But if it hits a rock,
you probably will be out of luck

Carancas was different because it never reached free fall, and the
impact was like whipping a piece of cement to belly flop against a hard
wall of something. Even then, a portion of material in the aft section
can survive. Try whipping pieces of chalk against a wall and you'll
demonstrate a similar effect and perhaps get some cone of material
stuck to the wall and a few crumbs falling back, along with a lot of
dust. If it is large enough, and traveling in a herd of rocks which is
also likely since they can become insultaed in their form in place
sublimation shield, the first stones will be sacrificial but some in
the back may survive. A possible explanation for Carancas. Or, just
that their were some laggers that fell behind the main bolus and their
higher surface area slowed them much more to better withsatand an
impact.

Kindest wishes
Douig

PS nice domain, Pete
PPS another way to produce some friable meteorites is let them fall in
water and see what happens and recover them later. After they dry out
enough material may be leached (since they are porous) that they become
much more friable. Care to give an example?



-----Original Message-----
From: Greg Hupe <gmhupe at centurylink.net>
To: Michael Mulgrew <mikestang at gmail.com>
Cc: The List <meteorite-list at meteoritecentral.com>
Sent: Mon, Oct 24, 2011 12:57 am
Subject: Re: [meteorite-list] Friable meteorites


Hey All,
I would have to suggest Nakhlites are one of the most friable
meteorites.

Best Regards,
Greg Hupe

On Oct 23, 2011, at 9:50 PM, Michael Mulgrew <mikestang at gmail.com>
wrote:

> Pete,
>
> If you want to talk friable meteorites, take a look at Tagish Lake.
> It is one of my most favorite meteorites, it is the least dense
> meteorite known to man. Fascinating!
>
> -Michael in so. Cal.
>
> On Sun, Oct 23, 2011 at 9:06 PM,
<pshugar at messengersfromthecosmos.com> wrote:
>>
>> In a conversation with someone today, it was mentioned that
>> Kilabo was extremely friable. Another really friable
>> meteorite was Caracas, Peru.
>> My question is how do they survive to the ground, to be found
>> not as a dust, but in large pieces? How did they make a crator?
>> Have the scientists figured out how the Caracas meteorite made
>> such a large crator?
>> Many questions and so little time to figure out what happened.
>> Pete
>>
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Received on Mon 24 Oct 2011 02:02:58 AM PDT