[meteorite-list] Carnacas smoke-trail photos

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Wed, 3 Oct 2007 01:45:51 -0500
Message-ID: <034301c80589$0af44c20$b92ee146_at_ATARIENGINE>

Chris --

The seismic measurement is of a 20-21 GJ event.
The Russian formulas for scaling crater energy,
developed from their work with the various sizes of
the Sikhote-Alin craters, would make it about 18 GJ.
The ground at Carancas is not merely wet soil, it is
wet rocky soil, a different kettle of resistance. You
can see the strata in the walls of the crater.

You specify a 5 GJ event, but your 10 ton and
1500 m/s example would have 11.25 GJ, not the
5 GJ you specifiy. Even a 5 GJ event would be
500 joules per gram of meteorite when it only
takes 100 joules per gram to powder even harder
terrestrial rock. The actual energy of the 10 ton,
1500 m/s example would be 1125 joules per gram
of meteorite, very close to the energy required to
completely melt ten tons of rock.

Of course, that's assuming all the energy is released
within the impactor and so, is only true for the leading
portion of the impactor. As the crater evolves, it takes
its share of the energy away.

The heat of vaporization for most earthly rocks is
around 18,000 joules per gram of rock. That's the
figure used to calculate vaporization for underground
bomb blasts. Silica is quite tough; it takes 22,000
joules per gram. Meteoritic material with a lot of
dissolved iron would also be hard to vaporize, but
after much Googling I can't find a value, so I will
be scientific and assume it's similar to the terrestrial
average. (Anybody know the actual figure?)

To be vaporized by a 21-22 GJ impact, a one ton impactor
would need ~6500 m/s impact velocity. In fact, for any
rock impactor to be vaporized, it needs to convert 18,000
joules of KE to heat for each gram, so roughly 6000 m/s
is the speed needed to vaporize any rock on impact,
regardless of its size. That's a high velocity to get all the
way to the surface.


Sterling K. Webb
---------------------------------------------------------------------
----- Original Message -----
From: "Chris Peterson" <clp at alumni.caltech.edu>
To: <meteorite-list at meteoritecentral.com>
Sent: Tuesday, October 02, 2007 9:49 PM
Subject: Re: [meteorite-list] Carnacas smoke-trail photos


Hi Michael-

As a physicist (and not on the scene), my instinct is simply to perform
some simple calculations to get some sense of what the various
possibilities are.

Assuming wet soil, which seems like what the crater was formed in, it
requires about 5 GJ (~1 ton TNT) to produce a crater that size. That
might reasonably be created by a 2 meter diameter, 10 ton stone
impacting at 1.5 km/s. Under those conditions, the impactor would be
largely converted to dust, but there would be little vaporization. A lot
of water could be vaporized, which would explain the cloud that was
seen, but there wouldn't be enough residual heat to boil water that
refilled the crater, or even make it hot.

Of course, it could have been a smaller object falling faster, or even a
rather large object (~5 meter diameter) falling at a 200 m/s terminal
velocity. The crater type would range from an explosive impact crater to
a simple excavated hole.

Distinguishing between these extremes will require getting soil samples
from around the crater extending at least a few hundred meters, as well
as collecting detailed measurements of the crater to determine its
precise shape. Unfortunately, the conditions don't seem ideal for
conducting this kind of research. Personally, I wouldn't be optimistic
about finding any large body in the crater, unless the actual impact was
subsonic.

One question involving the fireball: did the impact occur simultaneously
with the end of the fireball (which would imply a hypersonic impact of a
small body), or did the impact occur a minute or more after the
fireworks (which would suggest a low speed impact by a larger body)?
Anyway, keep up the good work, and collect whatever data you can. I hope
that the fireball was caught on a DoD satellite, and that the light
curve will be released. That would greatly assist in analyzing the
nature of the parent body.

Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com


----- Original Message -----
From: "Michael Farmer" <meteoriteguy at yahoo.com>
To: "Chris Peterson" <clp at alumni.caltech.edu>;
<meteorite-list at meteoritecentral.com>
Sent: Tuesday, October 02, 2007 6:59 PM
Subject: Re: [meteorite-list] Carnacas smoke-trail photos


Chris, it is a hell of a crater, at least 13 meters in
diameter, more than one meter of uplift, looks
identical to Meteor Crater to me, on a much smaller
scale.
There in fact does seem to be shocked material at the
crater, I found only inside and just outside the
crater, large pieces of compacted sandstone, yet there
is no sandstone there, it seems to have solidified on
the impact, everything else is more like soft mud.
Large, and I mean larger pieces of sod, weighing at
least 40 or 50 kilograms were thrown more than 50-100
meters, and smaller dirt clod debris thrown up to 15o
meters in all directions. This is a serious impact, I
mean you can call it what you want, but with the
uplift, the incredible debris field thrown to all
sides, the huge size, and volume of the crater itself,
certainly leads me to believe that the mass weighed
many tons and is obviously in the hole under some
meters of fallback debris. The locals report mushroom
cloud lingered for more than a hour.
As far as more pieces, this meterite came in over lake
Titikaka, and if you have never seen this lake, it is
HUGE! I would guess that as fragil as the meteorite
is, that tons of debris fell off but would most likely
have all fallen into the lake, or perhaps some on the
mountains just inside of Bolivia. It is not populated
there, and I assume from talking to most witnesses,
that the large main mass, which was a massive ball of
fire much larger and brighter than the Sun, caught
everyones attention pretty well, and would be so
bright that smaller pieces would be drowned out by the
intensity of the main mass. That is what I think
happened, surely many more pieces broke off but from
where the main mass hit, back down the flightpath is
nothing but swamps and high mountains for about 10
miles, then 15 miles of lake. Perfect for most
material to be lost.
Michael Farmer

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Received on Wed 03 Oct 2007 02:45:51 AM PDT