[meteorite-list] New Peru article

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Thu, 4 Oct 2007 03:16:47 -0500
Message-ID: <04be01c8065e$e9252fc0$b92ee146_at_ATARIENGINE>

Hi, Doug,

    Much has been made of the fact this is
"wet" soil. Yes, it has a high water table and
underground streams and so forth. But this is
high mountain plains ("Altiplano"), an ancient
limestone intermountain basin. The "soil" is
rocky. Several strata of rock are visible in the
crater walls. It's not a cushion.

    The crater depth is reported as just over
4 meters (as estimated by "poling"), but it
was already full of water when the first local
witnesses arrived, so that's an uncertain datum.

    I'd have to stand by my very much earlier
post on the energy requirements of meteorite
destruction and the velocities of that energy:

Energy to powder a "hard" meteorite =
100 joules per gram = 450 m/s.

Energy to melt a rock meteorite =
1,200 joules per gram = 1500 m/s.

Energy to vaporize a meteorite =
18,000 to 25,000 joules per gram = 6000 m/s.

    You're absolutely right that the crater takes up
the energy from the impactor. In modeling large
events, it seems that the imapctor and the target
share it almost evenly. But in small events, it doesn't
transfer as well and the impactor hogs most of it.

    The Carancas crater is from an impact equal to
perhaps 3 +/- 2 tons of TNT. The seismograph says
five tons TNT but includes the atmospheric "boom"
as well, so is exaggerated. The crater is characteristic
of a 1 to 2 ton TNT impact. But, let me bury five or
ten 50-lb cases of dynamite and I'll make you a bigger
crater than that. I would rate the crater as getting about
25% of the energy out of the impact, at most.

    The figure of 100 joules per gram to crush rock
is derived from Earthly rocks, like granite and such.
I wouldn't be surprised if this meteorite crushed at
far less pressure, "fragile and very porous," Mike
said. It would crush test at less than half the 100
joule per gram mark. Maybe much less. Gimme
a piece and I'll squash it in a strain guage; we'll see.

    "Deep" craters are not a mark of the excellent
cushioning qualities of the the target material, any
more than a "deep" bullet wound is the mark of the
excellent cushioning properties of the human body.
Frankly, the target material does not get much of a
voice in the result.

    The theoretical "ideal" crater is three times wider
than it is deep, and conical, for a "simple" crater
without rebound, breccia accumulation in the floor,
and all that other stuff. The Carancas crater is 13 m
by 4 m, or 3:1 just like the models, and conical. It's
a classic crater. It's not an impact pit; it's an explosive
crater.

    The cratering result is entirely (or 95%) the result
of the energies involved. Working out the models
showed that changing impactor material (iron vs. ice)
or the target material (sand vs. basalt) didn't change
the results at all. Energy rules.

> Even a three ton stone meteorite wouldn't be expected
> to maintain any cosmic velocity, and if it did by some
> stretch, it should have long sheered apart as it hit dense
> atmosphere.

    It's a miracle that ANYTHING makes it to the ground.
I think this was a very large object that ablated away, dropping
chucks the whole way, for tens of kilometers along the line
of flight. It just got to the ground before it was all gone. I
suspect a low entry angle helped.

    Mike described the boy's photos of the smoke trail from
Carancas, five miles away and said that after the boy took that
picture, he went to the crater. I put on my deerstalker. How
did he know where the crater was? At the time the meteor
flew over the village, no one knew the location of the crater.
The boy followed the smoke trail to the mushroom cloud,
I surmise. This would nean that the object ablated the whole
way to the crater and that mushroom cloud.

    This does not sound like a gentle impact to me. It sounds
like hypersonic ablative flight, a violently energetic impact,
a thermal explosive event, a thunderous boom of passage
(witnesses said it lasted for 15 minutes, but my guess it only
"seemed" like 15 minutes), a long persisting smoke trail.

    The highly nervous response and "illnesses" of the villagers
suggests a semi-traumatic event. We blab about big impacts
-- oh, boy! -- on this list all the time, but what would it be like
to be IN one?

    I know Mike is full of the dream of the "big one" down
there in the crater bottom, but so was Barringer, absolutely
convinced that there was a fortune in nickel-iron in the deep
basement rock of his crater. It's a dream that's easy to catch
and hard to give up. We'll see if the Peruvians come up with
anything.

    I'm betting against it.


Sterling K. Webb
----------------------------------------------------------------------
----- Original Message -----
From: "mexicodoug" <mexicodoug at aol.com>
To: <meteorite-list at meteoritecentral.com>
Sent: Thursday, October 04, 2007 1:23 AM
Subject: Re: [meteorite-list] New Peru article


Hi List amigos,

Just curious ... Sterling what model you have accounts for potato sized
meteorites (and powder) scattered in and around meters from the impact, yet
strictly powder inside, especially for a meteorite that sheds like this one
particularly along its natural 'fault' lines. Let me add that the collision
physics probably is greatly different as the ground is a great deal more
"compressible" than a typical collision where the rate of the speed of sound
traveling from end and back determines the stresses experienced. This is
basically the difference between dividing by zero time to dividing by an
extended time caused by the detrital inclusions in the energy absorbing
sink. The six meter depth of the crater in all likelyhood is an indication
of significant damping more than anything else. As is the great diameter a
testimony of the characteristic of the ability of the ground to absorb
shock. The difference between falling from an altitude to a marble floor or
a to bank of snow where you leave a big hole.

Even a three tone stone meteorite wouldn't be expected to maintain any
cosmic velocity, and if it did by some stretch, it should have long sheered
apart as it hit dense atmosphere.

Another random comment I have is that despite the observed peeing in the
crater, the marly clay soil is quite basic (pH = 7.8 vs. acidic), so we may
be lucky in that the meteorite remains preserved more than we think.

Finally, without any disrespect meant, I wanted to nominate the informal
name of this meteorite to be "the Pisco Sour meteorite" (even though it is
now quite alkaline).

Best health,
Doug

PS Randall, with all respect due and no malice intended, that joke you told
about the Arequipan Republic makes you as the joke teller a homosexual girl,
a result I don't think you intended (and please don't shoot the messenger).
Run by your wife the version you posted "exactly" and see if she busts out
laughing like we did. But hey a little joshing is good for the soul...


----- Original Message -----
From: "Sterling K. Webb" <sterling_k_webb at sbcglobal.net>
To: <meteorite-list at meteoritecentral.com>
Sent: Thursday, October 04, 2007 12:28 AM
Subject: Re: [meteorite-list] New Peru article


> Hi,
>
> The only good news here is that the notorious
> "meteoritotrafficantes americanos" have hopefully
> slipped across the bandit border into Boliva.
>
>> police had searched for the meteorite hunters
>> at their hotel but were unable to catch them
>> because they had left.
>
> I was thinking it was getting near the time to
> get out of Dodge; wasn't everybody? Mike, get
> out of there.
>
> It will be interesting to watch the local scientific
> authorities remove the massive multi-ton meteorite
> from the muddy pit, from under five meters of water,
> without draining it, as they said they would, before
> the crater vanishes in a few months (as they also
> said it would). Just kidding.
>
> Only problem is, after kicking numbers and
> reports around for a day or two, I don't think that
> there's anything under that mud but more mud.
> According to the INGEMMET report, the windows
> of a dwelling over 1000 meters away from the crater
> were broken and blown out by the impact. I believe
> that is diagnostic of a hypersonic impact (greater
> than 340 m/s).
>
> Using the figure for average terrestrial rock, it
> only takes about 100 joules per gram to powder it
> to dust. At the speed of sound, each gram of the
> meteoroid has 60 joules of kinetic energy; at Mach
> 1.3 (450 m/s), it has 100 joules per gram. At 1000 m/s
> (or about Mach 3), it has over 500 joules per gram.
>
> Mike Farmer said, "The meteorite is very fragile,
> very porous..." I doubt very much that it would take
> 100 joules (granite takes 100 joules) to be dusted.
> Mike also mentioned locally taken photos that showed
> "incredible amounts of meteorite powder."
>
> And lastly, it seems from those photos Mike saw
> (and the photgrapher's story) that the fireball's ablative
> smoke trail was visible pretty much all the way to the
> crater location and the mushroom cloud. That would
> mean that the object was in ablative flight all the way
> to the ground. (It's worthwhile to point out that ablation
> requires more than "merely" hypersonic speeds.)
>
> Then there's Dr. Daniels a.k.a. Gregory's report of
> the tiny dust-like particles he meteoritotrafficanted from
> a little old lady -- that's evidence that the crushing strength
> of the material was exceeded, and because it was outside
> the crater, must have come from the most protected
> part of the impactor: its backside.
>
> That meteorite is dust. No matter what it massed,
> there's nothing in that mudpit.
>
> And it's OK with me if I'm wrong and somebody
> winches a ton or two of meteorite out of the mud; it
> would be a great day. But... don't hold your breath.
>
>
> Sterling K. Webb
> --------------------------------------------------------------------
Received on Thu 04 Oct 2007 04:16:47 AM PDT