[meteorite-list] Carnacas smoke-trail photos

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Tue, 2 Oct 2007 20:26:52 -0500
Message-ID: <02fc01c8055c$7b1bf8e0$b92ee146_at_ATARIENGINE>

Hi, List,

Michael Farmer wrote (earlier):
> It MUST be more than 3 or 4 tons, the crater is huge,
> much larger than Jilin main mass crater, there were
> pieces of sod (maybe 40 kilograms chunks of hard soil)
> thrown more than 100 meters in every direction... It is
> simple physics to know that the mass which made
> that crater must weigh many tons.

The question is this: is this an "impact pit" or a "crater"?
An impact pit is just a hole excavated by the physical forces
exerted by a great mass traveling at high speed. Jilin is an
almost-impact pit. Photos of the dig-out can be found at:
http://www.planetarium.montreal.qc.ca/Information/Expo_Meteorites/Vedettes/jilin_a.html
Jilin, despite the 1700 kg weight of the impactor, could
never be confused with a crater. The pit was 6 meters
deep, yes, but only 2 meters wide. The slow moving and
durable Jilin did little more than poke a deep hole. Big rock,
little hole.

So, what is a crater? A crater is just a hole excavated by the
physical forces of a body so energetic that it transforms itself
into a gas or even a plasma, at terrific heat and pressure, which
"blows out" a hole in the ground. While the morphology of craters
vary with the strength and distribution of ground materials, in
the ideal case, the "hole" is conical in shape. The ratio of width
to depth varies with the nature of the surface and the energy
content of the impactor. Big hole, little rock.

Which is Carancas?

The photo provided by Randall Gregory clearly shows the shape
of the crater to be conical. The depth-width ratio is low, certainly
less than 3:1, perhaps as low as 2.25:1. (It's hard to calculate wall
angles from a re-photographed photograph!) Here's the photo:
http://webpages.charter.net/garrison6328/titicaca/DSC00035.JPG

In the article cited by Paul and reprinted from New Scientist:
http://www.signs-of-the-times.org/articles/show/140757-Mysteries+remain+over+Peru+meteorite+impact ,
quotes a
report by Macedo and Machare that there is a one-meter "raised
rim," visible in other photos. Usually, this is a sign of a very
energetic event. However, the "rim" and upper strata are not tilted;
the "rim" is piled dirt pushed out of the hole by the impact, but not
energetically enough to be thrown out over the landscape.

The article further says "Jackson thinks the kinetic energy of
impact could have generated the heat, and is trying to find
seismic records of the crash. Schultz says the heat and bubbling
might have come from air trapped and heated on the "front" of
the meteorite as it sped through the air."

Schultz is a geologist at Brown University, but his is a silly
suggestion. Jackson (Geological Survey of Canada) has a
more interesting suggestion. If the stone was just the right
size for its velocity, the back would have spalled on impact, the
front would have vaporized and blown out the crater, and
some portion of the middle could have melted and trapped
some of the impact energy to be dissipated by boiling the
water that flowed in immediately for a few minutes.

The likelihood of this scenario has a very narrow window of
possibility and would only happen in a true "borderline"
event between an impact pit and a crater. Much more likely
is that the impact was energetic enough to heat the wet
soil and ground water well above the boiling point, and any
melted rock that is found is more likely to be local rock
melted by the impact, rather than meteoritic rock. This
implies a high-energy event.

There is a "borderline case" in the literature of recent falls:
http://adsabs.harvard.edu/abs/1992AVest..26...82P
The Sterlitamak crater, is 9.4 meters and was formed on
May 17, 1990 by a one-ton iron object. While every impact
differs from others, a description of that crater is of interest:
http://adsabs.harvard.edu/abs/1992Metic..27R.276P
    "The Sterlitamak meteorite fell on May 17, 1990 at 23h20m
local time (17h20m GMT) and formed a crater in a field 20 km
westward of the town of Sterlitamak (Petaev et al., 1991).
Many witnesses in South Bashkiria saw a very bright fireball
(up to -5 magnitude) moving from south to north at a ~45
degree angle to the horizon. Witnesses located ~2 km from
the crater observed the fireball glowing right up to the time
of impact, after which several explosions were heard. The
crater was found on May 19. From witnesses' reports, the
fresh crater was 4.5-5 m in depth and had sheer walls ~3 m
in height below which was a conical talus surface with a hole
 in the center. The crater itself was surrounded by a continuous
rim 60-70 cm in thickness and by radial ejecta. Our field team
arrived at the crater on May 23, six days after its formation.
We found the crater in rather good condition except for
partial collapse of the rim, material from which had filled
in the crater up to ~3 m from the surface. The western wall
of the crater was composed of well-preserved brown loam
with shale- like parting dipping 25-30 degrees away from the
crater center. A large slip block of autogenic breccia was
observed along the eastern crater wall. An allogenic breccia
composed of a mixture of brown loam and black soil was
traced to the depth of ~5 m from the surface. Outside the rim,
the crater ejecta formed an asymmetric continuous blanket
and distinct radial rays. The southern rays were shorter and
thicker than the northern and eastern rays. About 2 dozen
meteorite fragments, from several grams to several hundred
grams in weight, were recovered in the crater vicinity. A search
for other meteorite fragments or individuals at distances up
to 1 km southward from the crater was unsuccessful. Two
partly encrusted fragments (3 and 6 kg) with clear
Widmanstatten pattern on a broken surface were found at
a depth of ~8 m during crater excavation. In May of 1991
a 315-kg partly fragmented individual was recovered at a
depth of ~12 m. This sample is a 50 x 45 x 28 cm block
with front, rear and two adjoining lateral surfaces covered
by regmaglypts and thick (~0.5 mm) fusion crust. The
other two surfaces are very rough, contain no regmaglypts,
and have a thinner fusion crust. The preimpact shape of
the meteorite may be approximately modeled as a slab
~100 x 100 x 28 cm. An estimate of the projectile mass
was made based on the crater dimensions. From the
relationships between crater diameter and projectile mass
determined for the Sikhote-Alin craters, the impact mass
of the Sterlitamak meteorite is estimated at ~1 ton (Petaev, 1992).
A separate estimate, based on cratering energy, yields a total
mass of ~1.5 tons (Ivanov, Petaev, 1992). A comparison of
the estimated projectile mass and the weight and morphology
of the individual recovered suggests a fragmentation of the
projectile in the atmosphere and the formation of the crater
by the impact of an agglomeration of individuals. The other
fragments of the projectile are still in the crater."

http://www.somerikko.net/old/geo/imp/refer.htm
"Observers claim that the fireball actually hit the ground.
Impact velocity was estimated to be over 2 km/s and impact
force was equal to 1 ton of TNT. Meteorite made 9.4 meter
wide and 3 meter deep crater into a potato field. Impact
(shockwave of falling meteorite) destroyed potatos in a
area of 100 meter in radius. A 300 kg meteorite was recovered
from 15 meter below surface and it is estimated that there
should be at least one ton more meteorite but deeper in the
ground."

Because Sterlitamak was an iron and didn't explode, it is
intermediate between a deep pit and a true crater. It doesn't
make a good comparison with the Peruvian crater. That
crater was formed by a stone and certainly didn't penetrate
the ground the way an iron would.

We need to think about kinetic energy. Ready?

Energy to powder a "hard" meteorite = 100 joules per gram.
Energy to melt a rock meteorite = 1,200 joules per gram.
Energy to convert a meteorite to vapor or even plasma?
Priceless, er, I mean, say, 50 or 100 times as much: 50,000
or 100,000 joules. A gram of actual TNT releases only
4184 joules of energy. Kinetic energy is a potent explosive!

How much kinetic energy can a meteorite carry?
At the theoretical maximum encounter speed of 73,400 m/s,
5,200,000 joules per gram! At the minimum theoretical
"fall to earth" speed of 11,200 m/s, about 120,000 joules
per gram. At three times the speed of sound (1100 m/s),
about 1200 joules per gram. or just about enough to melt
the average rock.

So, you see, the fact the meteorite is "cold" when it's
moving is irrelevant if it carrying around enough kinetic
energy to melt itself. It's like a suicide bomber, a wet,
cold, biological mass that turns into a hot, gaseous,
energetic sphere. Turn kinetic energy to thermal energy
and hot liquid rock results, or explosive trapped rock
vapor, or 50,000 degree K. plasma.

The presence of fragments outside the most explosive
crater does not mean the event was not of a very high
energy. Surviving fragments of the impactor are spalled off
the back of the impactor by the explosive violence of the
main body (front and center) being converted from a cold
solid to a very hot gas in microseconds. The famous Meteor
Crater is a fine example. Millions of tons of iron were
vaporized (or "plasmasized"), but tons of solid iron were
scattered over "the range" that surrounds it, all spalled.
But, such "spalling" can also happen with low energy events
as well. They can be distinguished by how far away you
find spalled fragments, another piece of data we don't have.

I hope Mike Farmer (or anybody) saved or sieved the dirt
just outside the crater rim at various distances. If it contains
micro-sized glassy or metallic spherules (or both), there was
a vaporizing event, and the spherules would be the vapor that
cooled quickly in the air (hence "glassy") and fell into the soil.

The "seismic" footprint of the event was reported as the energy
equivalent to 5 tons of TNT, or 10^11 joules. If you like zeroes,
that's 100,000,000,000 joules. Divided amongst a ton of meteorite
(a million grams), it's still 100,000 joules per gram of meteorite,
more than enough for a good plasma explosion of the whole
object! Even at a five ton object, it's still enough for the vaporizing
explosion. This implies that only spalled product will be found.
No massive remnant would remain. This seismic estimate found
make Carancas five times more energetic than Sterlitamak. The
size of the Carancas crater implies roughly three tons of TNT,
in a pretty good agreement of the five ton seismic figure.

To throw a 40 kg chunk 100 meters is like what a catapult
does and requires only a few thousand joules (depending on
how high you want to loft it), and if that seismic measurement
is reliable, there were plenty of joules to go around! Did anyone
walk out a distance greater than 100 meters to see what sizes of
chunk would be found at greater distances? Even a crude notion
of distribution would give a magnitude estimate of the explosion.

We cannot approximate mass from the force of the crater-forming
explosion; only the total energy involved. Identical energies can be
achieved by large slow objects and small fast objects. However,
the majority of the indicators is that this was a high energy event,
more than enough to have completely vaporized the impactor
(exceot for the spalls).

>From this most recent email of Mike's and the analysis above, I
would estimate this impactor to be a 1.5 to 2.0 metric ton object
still in hypersonic flight (Mach 5-7). The indication is that there
isn't any "big one" IN the crater. Now, if it HAD been an iron...


Sterling K. Webb
------------------------------------------------------------------------------
----- Original Message -----
From: "Michael Farmer" <meteoriteguy at yahoo.com>
To: <meteorite-list at meteoritecentral.com>
Sent: Tuesday, October 02, 2007 5:54 PM
Subject: [meteorite-list] Carnacas smoke-trail photos


I was lucky enough to learn that teenager was able to
take a photo of the Carancas meteorite smoketrail, and
I purchased the right to copy and use that photo.
I will post this when I get home, and it belongs to
me, please do not use it without my permission. I gave
him enough to buy a new camera and take 1000 more
photos. He saw the fall, grabbed his camera, snapped a
photo of the corkscrew smoketrail, then went to the
fall site some 5 miles away. The other photos were
very poor, so I did not use them, but they showed the
crater filling with water, and many chunks of
meteorite in the crater walls, as well as incredible
amounts of meteorite powder. He also had a photo from
a distance of more than 2 kilometers where you could
see a smokecloud which looked like a small mushroom
cloud which he confirmed was the steam coming from the
crater. That photo was visible, but too poor for me to
use as I could not copy it and see the detail.
Is it indeed possible that a mass of say 3-7 tons
could cause such intense heat on impact? We think that
the compression of the soil, in an instant to many
meteors deep could also cause intense heating.
Every person we interviewed decribed boiling water,
lots of steam, and horrible sulfer type smell. The
media of course, hyped the crap to levels that were
bordering on insane.
Michael Farmer
Received on Tue 02 Oct 2007 09:26:52 PM PDT