[meteorite-list] Carancas vs. Canyon Diablo?

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Wed, 17 Oct 2007 04:40:21 -0500
Message-ID: <0ab001c810a1$bd400e50$b92ee146_at_ATARIENGINE>

Hi,

    I wasn't making a comparison between Carancas Crater
and Meteor Crater and invoking any similarity -- vastly
different events. But I was putting the case of D. M. Barringer
forward as an example of the strength of the psychological
attraction to the idea of the survival of the meteorite body.
Some people just want it to be so, against all evidence.

    G. K. Gilbert, who first investigated Meteor Crater,
understood very quickly the true course of what happened
there; Barringer never accepted it. All of Barringer's co-
workers resigned themselves to the evidence of vaporization
eventually. It was always obvious to Nininger.

    I'm just pointing out that psychological phenomenon.

    There is no evidence of a gentle impact in Carancas,
and plenty of evidence of an energetic thermal event. The
chances of any survival of the impactor seem very small.

    1. The odors, fumes, noxious vapors, etc. reported
by all the witnesses (who may well have reacted hysterically
to them) are easily explained by the vaporization of the
troilite (5% of the stone), an event that requires temperatures
in excess of 700 degrees K. Dissociation of the troilite is
more or less automatic if it vaporizes in the terrestrial
environment. This vapor explosion would be quite sufficient
to eliminate the impactor. Note that 700 K. is only a minimum
thermal level; it could be more energetic.

    2. The various witness reports: a man knocked over at
300 meters, an event that requires a high level of overpressure;
windows broken in Desaguadero, 10,800 meters away; two
domestic animals, closer than 300 meters, killed by the blast
(gentle impacts do not have kill zones); a universally observed
"mushroom cloud" (!) -- none of it suggests a "soft" landing
to me.

    3. The extreme weakness of the stone (you can break it
in your hand using only human muscles) makes the survival
of "pieces in the pit" very unlikely in an event with the above
characteristics. It's too late at night for furious calculation,
but the energy required to pulverize this impactor is tiny
compared to that of even the most modest and moderate
impact.

    Doug, there is no set percentage for back spall. Since it
is caused by the shock wave of initial impact passing back
through the impactor, it depends on a) the speed of the impact,
and b) the strength of the stone. We don't know that speed;
we do know the stone is very weak, but there's no way of
"back-calculating" from the recovered extra-crater mass to
the mass of the impactor (drat!).

    Rob, the absence of any evidence of fragmentation puzzles
me as much as it seems to you. How could a big object of
such friable material NOT drop numerous secondaries? There
should be some evidence of a "shower," a kind of miniature
Holbrook over Peru, but there isn't. This stuff should have
disintegrated in flight. But no witness mentions fragmentations,
dropping pieces, etc. There are no secondary pits, no reports
of material found in nearby locations, and the rest of it. By
now, it's safe to assume the locals (who range widely since
they are pastoralists) would notice and recognize more
meteorites if they found them.

    The only explanation I can think of is that it was a very,
very steep descent and there was little angular separation of
any fragments (and I ain't happy with that, myself, but it's
all I got).

    The only thing I said about the dimensions of the crater
or pit is that they appear to be classic (3:1, 30 degree slope,
etc.). If it's an explosive crater, it's easy to calculate the
kinetic energy required. If it's a mass displacement pit, we
need to see a really big object sitting in it... really big. If
you think the impact speed was slowly subsonic, we need a
10 or 20 ton object to excavate the 350+ tons that were
removed from the crater and spread in an ejecta blanket
that covers 500,000 square meters. (Good sized pit, eh?)

    Visually, after the fact, there is little if anything to show
whether a hole in the ground is a crater or a pit, whether it
was hot or not, whether it was small and moving fast or big
and moving slow. An obvious relict multi-ton meteorite,
Brown's "ten-ton monster," would, but I don't see one.
A crater this size isn't going to produce the flashy stuff
that big craters do. And an impact event tends to erase its
own history and delete its own data.


Sterling K. Webb
----------------------------------------------------------------------
----- Original Message -----
From: "mexicodoug" <mexicodoug at aol.com>
To: "Rob Matson" <mojave_meteorites at cox.net>;
<meteorite-list at meteoritecentral.com>
Sent: Wednesday, October 17, 2007 2:19 AM
Subject: Re: [meteorite-list] Carancas vs. Canyon Diablo?


Hi Rob, Sterling and List,

Thanks for the reality check Rob, a.k.a. that pesky detail called
conservation of mass that insists on being respected even in sexy mudpits.
Sterling, what % is spalled backwards in these (much-to-be-desired) models
of such low-end impact energies in somewhat "amortizing" soils? For
argument sake let's say that 50Kg of powder and fragments were tossed out
before being enveloped by the mountain pudding.

Best Health,
Doug


----- Original Message -----
From: "Rob Matson" <mojave_meteorites at cox.net>
To: <meteorite-list at meteoritecentral.com>
Sent: Wednesday, October 17, 2007 1:52 AM
Subject: [meteorite-list] Carancas vs. Canyon Diablo?


> Hi Sterling,
>
> I am little perplexed why you persist in comparing the Peru
> event to Meteor[ite] Crater, when the two events share very
> little in common other than an extraterrestrial origin. The
> energies involved are many orders of magnitude apart; without
> pulling out a hand calculator I would guess that Park Forest
> was a closer match to Carancas than Canyon Diablo.
>
> For me, there is nothing about the dimensions of the impact
> pit (I refuse to call it a crater) that precludes a significant
> mass of meteoritic material buried within. Yes, this mass is
> likely in many pieces, but I don't see how the collective can
> avoid weighing less than a metric ton.
>
> You seem to believe that hitting the ground was somehow more
> stressful to this meteoroid than hitting the upper atmosphere.
> If so, that would be a first.
>
> Best wishes,
> Rob
>
>
>
> ______________________________________________
> Meteorite-list mailing list
> Meteorite-list at meteoritecentral.com
> http://six.pairlist.net/mailman/listinfo/meteorite-list
>

______________________________________________
Meteorite-list mailing list
Meteorite-list at meteoritecentral.com
http://six.pairlist.net/mailman/listinfo/meteorite-list
Received on Wed 17 Oct 2007 05:40:21 AM PDT