[meteorite-list] Carancas: Impact crater vs. impact hole

From: Jose Campos <josecamposcomet_at_meteoritecentral.com>
Date: Sun, 21 Oct 2007 17:13:38 +0100
Message-ID: <004001c813fd$5852e3a0$68109859_at_paular2wuci4vh>

Hi Sterling, Bernd and List,

The iron impactor versus a stone impactor mentioned in the email, is a very
interesting concept!

As a matter of interest and regarding the Carancas meteorite impact, has
anyone taken taken pics. of the reported mushroom cloud mentioned in your
email?
Regards,
Jos? Campos


----- Original Message -----

From: "Sterling K. Webb" <sterling_k_webb at sbcglobal.net>
To: <meteorite-list at meteoritecentral.com>; <bernd.pauli at paulinet.de>
Sent: Saturday, October 20, 2007 10:19 PM
Subject: Re: [meteorite-list] Carancas: Impact crater vs. impact hole


> Hi, Bernd, List,
>
> An excellent attempt at defining the difference,
> but as Bernd has pointed out there are characteristics
> of both in Carancas. But, Buchward is seeing things
> from an "iron" perspective.
>
> An iron will make a much larger "impact pit"
> than any stone ever could, as it takes much more
> energy to vaporize iron than it does to vaporize rock.
> (The boiling point of iron is 3134 degrees Kelvin,
> almost double that of even the toughest rocks.)
>
> In practical terms, an exploding (vaporizing)
> iron impactor would probably have to hit at 8 to
> 10 km/s to create a vaporizing explosion. Buchwald
> mentions a velocity of 5 km/s as an upper limit to
> an impact pit. This is because if all the impact energy
> were converted to heat with full 100% efficiency, it
> would take a 4.2 km/s impact to vaporize rock. In a
> real impact, it would take 5 km/s or more to do it.
>
> In practice, if we had a vast range of craters to examine,
> we would find "true" craters made by stones that were
> smaller than any "true" crater made by irons, and iron
> impact pits larger than the smallest "true" craters made
> by stones.
>
> There's an interesting complication not often thought
> about: an iron impact with insufficient energy to vaporize
> its own iron can be "hot" enough to vaporize the terrestrial
> rocks it impacts! So, it's possible that an iron impactor
> could produce a vaporizing cratering explosion that leaves
> the impactor (partly) intact! Perhaps this type of crater
> would occupy the intermediate range between stone and
> iron craters in the case of iron impactors.
>
> Carancas had "vaporizing" traits: the reported "bright
> flash," the mushroom cloud, and the mysterious vapors
> all point to a thermal event, but other signs of the heat of
> a rock-vapor explosion event are missing. I believe that
> what happened is that only the 5% (to maybe) 10%
> troilite component of the impactor vaporized (an idea
> first posted on the List by Piper R. W. Hollier -- going
> to be academic here and credit my sources).
>
> Troilite vaporizes at a much lower temperature than
> rock -- only 427 degrees C. -- but it would produce a
> very satisfying explosive shock, excavating the crater,
> powdering the impactor, releasing hot sulfur into the
> air and the "wet" crater. Troilite is almost unknown in
> the terrestrial environment because it breaks down
> rapidly at Earth-normal temperatures; vaporized troilite
> would chemically combine almost instantly. Even the
> "bubbling" in the crater, which everybody immediately
> dismissed, can be explained by the short-term reaction
> of the troilite-generated (dilute) sulfuric acid in the crater
> with the native carbonates and the production of
> hydrogen sulfide.
>
> As for what might be found in the crater itself, I
> suggest that nothing but the free iron component will
> have remained there, probably having penetrated the
> crater "bottom" as far as the native rock allows. Early
> descriptions of big pieces picked by local institutions
> show a 15% free iron content, much of it (by weight)
> in large irregular concentrations (like Portales Valley).
> That portion is likely in (or under) the crater still. IF
> it were a ten-ton impactor, there could (might) be a
> ton of iron down there. (Notice I used the big "if.")
>
> This type of "semi-vaporizing" explosion has never
> been proposed before as far as I know, but the fit of this
> "theoretical" model to Carancas is extremely convincing.
> (Well, I'm convinced anyway.) An investigation of this
> impact could actually contribute something to our scant
> knowledge of impact mechanics in the real world, but
> instead (if the MSNBC article is to be believed) we get
> "ho-hum, another boring H4/5." My, are we spoiled,
> or what?
>
>
> Sterling K. Webb
> --------------------------------------------------------------------
> ----- Original Message -----
> From: <bernd.pauli at paulinet.de>
> To: <meteorite-list at meteoritecentral.com>
> Sent: Saturday, October 20, 2007 11:40 AM
> Subject: [meteorite-list] Carancas: Impact crater vs. impact hole
>
>
> Hello All!
>
> BUCHWALD V.F. (1975) Handbook of
> Iron Meteorites, Volume 1, pp. 33-34:
>
> For the sake of clarity it should be noted here that
> giant meteorites can form two types of craters.
> The smaller crater is more properly called a large
> impact hole and is geerated by relatively small
> meteorites (< 50 tons) with relatively low velocities
> not exceeding 5 km/s. Such meteorites cause
> mechanical destruction of the ground and are themselves
> usually broken into a number of fragments
> upon impact. The major part of the meteortic fragments
> will remain in the impact hole with
> shattered rock and soil. Typical examples are the
> 100-1,700 kg iron meteorites of the Sikhote-Alin
> shower that produced impact holes 6-27 meters in
> diameter and buried themselves to depths of 2-8 meters.
> The genuine craters discussed here are more than
> 100 m in diameter and were formed as the result
> of an explosion at the moment of impact. The
> projectile itself vaporized almost entirely, and
> tremendous shock waves raced outward from
> the focus.
>
> ********************************************************************************
>
> As if to find a compromise between list members
> who differ on what to call Carancas, the
> associated "hole" in the ground there obviously
> unites characteristics that place it inbetween what
> should be called an impact hole and an impact crater.
>
> What a pleasant coincidence! ;-)
>
> Bernd
>
> ______________________________________________
> 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
>
>
> --
> No virus found in this incoming message.
> Checked by AVG Free Edition.
> Version: 7.5.488 / Virus Database: 269.15.3/1081 - Release Date:
> 19-10-2007 17:41
>
Received on Sun 21 Oct 2007 12:13:38 PM PDT