Hi Sterling, my brief comments are inserted in your text in all lower case,
Hola, Doug,
I think the variety of reports I've already posted
and then referred to several times, are all that I can
say to your dislike for my reconstruction of the
event. I confess to being somewhat mystified by
your comments.
i am not focused on your reconstruction of the event. just your comment
that everything in the crater is pulverized due to the incredible energy
released in impact. while this is a possible scenario, i hope more intact
material can be found. my objection really is the tendency for people to
jump to conclusions ruling out other posibilities based on heresay. i've
read the same reports you have over the same time period and cannot see any
clear cut evidence as you do. that's what i enjoy about the list, the
ability to debate all sides of a problem openly and come away with a new
angle in the process. plus the bickereing was getting to me so this was a
nice opportunity to contribute.
The size of the crater, which is rare or even unique...
Quite to the contrary, it is a textbook normal conical
simple crater with a width/depth ratio of 3:1 (13.4 meters
wide and 4+ meters deep), just like "ideal" theoretical
crater.
sterling, on earth, this crater has few if any known peers. I said size. i
did not mentioned anything about proportions.
A much better comparison, btw, is Jilin.
The Carancas crater bears no resemblance to Jilin,
none whatsoever. Jilin is not a crater. Jilin is not even
an impact pit. Jilin is a hole 6 meters deep and less than
2 meters wide. Jilin is a good example of your previous
metaphor of a marble dropped in a snowbank. It was
so slow-moving that it just poked a hole in the dirt.
jilin, nevertheless, is the largest individual stony meteorite to ever land
and be recovered, and we suspect it to be more comparable in size and
composition. trust me - that ton of rock just didn't land like a feather on
a waterbed, either.
what model you have accounts for potato sized
meteorites (and powder) scattered in and around
meters from the impact
The "incredible amount of meteorite powder" Mike
mentioned is not a derivation from a model; it's a witness
statement by someone who was there, an expert witness
at that.
ok. so i now understand your opinion hidden behind the tireless search
engine and fine postings - which is just that - opinion. because there is a
lot of powder around you think everything in the hole must be powder because
we get this graceful, textbook idealized impact that fits the barringer
crater. mike also was an expert witness to all the powder when a small
fragment of moss landed on the concrete in an industrial complex. still he
believed a meteorite is in the crater...so your logic is back to mike saw a
lot of powder and barringer crater had no big meteorite buried, so this is a
barringer situation.
The mechanism is back-spalling. The shock wave of
impact, originating at the point of impact, extends both
forward into the target material and backward through
the impactor. If the speed of impact exceeds the speed of
sound in the meteoritic material, the expanding shock wave
shreds the meteorite and pushes the distrupting material
back, away from the impact.
ok. something to think about at last. mike mentions many other theings -
the meteorite may have punched a hole into the water table below, too. as i
mentioned yesterday, the speed of sound controlling this idealized process
is significantly compromised when you don't get a dead stop. that was the
purpose of my comments yesterday you followed-up. please keep an open mind
when you mention the hole is strictly filled with powder and contains no
fragments.. your reconstruction isn't a reconstruction at all in the
scientific sense, as we lack too much at this stage to model it seriously
and that is why i am bothering to respond to this interesting discussion
which would determine whether there are more sustantial meteorites in the
hole - a very interesting question worthy of debate.
[I insert here the fact that the few tests that have been
performed on meteorites show that the speed of sound is
less in meteorites than in comparable terrestrial rocks. The
more porous the meteorite, the slower the speed of sound
in it. Carancas was a dead duck, I'm afraid.]
these negligable differences between meteorite and terrestrial are unlikely
to make the difference and i don't think you mean that either.
In a truly violent impact, only the central rear portion of
the impactor survives as fragments. In less violent impacts,
the rear quarter, third or more of the impactor is fragmented
and ejected backwards (along with the powdered material
closer to the point of impact). It is found radially distributed
around the crater (or asymetrically if an oblique impact).
maybe. these are all based on models and you are assuming an idealized
'truly violent impact' which is not an easy order. but we have perhaps 6
meters of penetration that still isn't "violent" in the terms of a Barringer
crater type scenario. A rim will get created whenever you excavate ... it
is partially a reflection of a gaussian distribution of displacement of
strewn material. i wouldn't read any more into this, though if i did it
would make for a good Science fantasy plot.
I mentioned Canyon Diablo because Nininger first
elucidated the mechanism, I believe, although I cannot cite
chapter and verse. Googling, I discover that Jay Melosh
claims to have discovered it. Shame, shame. How quickly
they pick, not your bones, but your ideas... once you're dead.
http://www.gsajournals.org/perlserv/?request=get-document&doi=10.1130%2F1052-5173(2002)012%3C0029%3AGKGA%3E2.0.CO%3B2&ct=1
Melosh's "Impact Cratering: A Geological Process" is
the standard work on impact mechanics. Amazon Canada has
used copy for only $665.77. I guess it's priceless knowledge.
Well, no; it has a price. And not in crummy US dollars either,
but those rare and valuable Canadian dollars!
yup, it would be nice to have an endowment for a better library. and i
appreciate your pet subject of jay melosh's impact modeling. does he have an
impact calculator somewhere on the internet you can provide a link for, that
includes the assumptions of his high energy violent models?
the ablative path for most meteorites stops much, much
higher than 3800 meters!
I cited the witness evidence that indicates the ablative path
continued to, or very near to, the crater, so this is another ditto.
we also have witness evidence of boiling cauldren pits. in the excitement
is is easy to get carried away. dust sloughing off the rock in free fall
after its violtent entry commonly causes dust trails and is a likely
explanation, as well. if it truly were ablating down to the ground, i think
we would have some nice impact glasses or spheroids!!! now if mike saw
those, i'd be in your camp.
And if it was ablating to the ground, it clearly wasn't in free
fall. I quote Jose Machero of INGEMMET (which I've done
before):
"There was a strong explosion that was felt up to
Desaguadero city 20 km from the impact site. Some window
glasses of the Local Health Center (at 1 km from the site)
were broken."
An impact that was felt 20 kilometers away does not sound
like "free fall" to me.
ok, so there were some strong sonic booms. we don't know if they are from
the impact alone or flight alone or what. let's not get too carried away by
reports we need to be a bit skeptical about if we ever expect to get this
straight. the sonic booms for such a big meteorite can be big. an maybe
they forgot to caulk the windows. i know what that is like. every time a
car passes my place the windows begin to whine like the door is falling
down. (past tense, i siliconed them)
I really like the graph.
thank you. perhaps it shouldn't be buried in these messages as it goes a
long way to answer some questions that sometimes pop up on the list.
May a Lunar fall gently in your back garden.
thanks, again, and to you may a well oriented Venisian grace the mantel
above your hearth.
further comment. truly there is no reliable basis to discount the
probability of bona fide fragments in the crater. i have nothing against
your scenario as long as the mind remains open to the simplier though
debatably less dramatic explanations. in any case a couple of tons falling,
like in the case of Jilin, will certainly come in with a bang. i do believe
that this space rock impacted at about double the energy it would have at
free fall at sea level, due to the faster free fall velocity it had in the
air which is 38% thinner at 3800 meters. at this stage, a neat, supersonic
impact throughout the collision seems highly unlikely to me, even if the
free fall velocity was near the speed of sound initially. we can check free
fall velocity for a one meter sphere -that's two tons, btw. i think i put
the formula on the list in 2003 if you don't want to look for or derive it.
as i mentioned in my only post yesterday, if you double the time of impact
you half the rate of transfer of energy. the time of impact was probably
significantly increased due to the characteristics of the soil.
the great thing is, if the folks responsible for the crater now will do
their homework, we will get a definitive answer one way or another and can
revisit this issue with a refreshing investigative basis rather than the
usual unreliable accounts during the excitement..
Sterling K. Webb
best health,
doug
--------------------------------------------------------------------------
----- Original Message -----
From: "mexicodoug" <[EMAIL PROTECTED]>
To: "Sterling K. Webb" <[EMAIL PROTECTED]>; "Meteorite List"
<[email protected]>
Cc: <[EMAIL PROTECTED]>
Sent: Thursday, October 04, 2007 9:39 PM
Subject: Re: [meteorite-list] Entry Dynamics in Peru
Not so fast Sterling :-) The size of the crater, which is rare or even
unique... doesn't make mucked-up analyses a requirement!
Short and simple as I just read your reply to me in which you somehow
missed
the central point I asked about when you insisted that the crater contains
nothing but powder...let's take a little more of a scientific approach.
My prior post began, "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."
Please answer that question clearly for my benefit rather than skipping
and
speaking of Canyon Diablo and Barringer. A much better comparison, btw,
is
Jilin.
As to the ancillary stuff...
Congratulations on ace Mountaineer Mike Fowler who mentioned that 50% of
the
atmosphere is under 3.5 miles elevation - it jives within 100 meters to
the
calculation I worked on and gives me the confidence I need for checking
this
calculation. When you state that "only" 58% of the atmosphere's mass was
in
the path of the Peruvian meteorite, just to keep a sensible argument
going,
I would suggest you don't introduce bias via adjectives like "only" into
the
interpretation. There is an incorrect implication that in this last 2
miles
of atmosphere, cosmic velocity is typically damped. ---not true.
According to my numbers, your 58% estimate was ok for the back of an
envelope, though a little exaggerated. I calculated it to be 62.1% using
a
more accurate model (which agrees to M. Fowler's 3.5 mile figure within
100
m) for the atmosphere than your barometric formula. Rather than dump a
bunch of numbers on the list, let me just share this graph, which I just
generated that is useful from sea level to 25 kilometers altitude, so you
can graphically see how much atmospheric mass is traversed for any bolide
around at the Peruvian crater's around October. Don't forget that the
ablative path for most meteorites stops much, much higher than 3800
meters!
www.diogenite.com/Huanocollo.gif
This graphically gives a great idea of how much % of the atmosphere any
meteorite anywhere on Earth passes through to get to any altitude above
sea
level, and if you look at it you can see how much of a fraction of the
atmosphere mass is traversed in any segment of the travel from 25Km on
down.
Just compare the blue area to the white and you get the idea of of the
FRACTION of the atmosphere traversed. No arithmetic needed - the ratio of
blue to blue+white is the % of the atmosphere for any geographical
elevation
and includes luminous paths too..
Sorry, but I can't accept your dismissing unscientifically the arrival of
any meteoritical material generally to the ground as difficult to on one
hand and then on the other calculate all these asides to things even you
don't want to know to such precision! 62% is 62%, not "only" anything.
62%
of the atmosphere is only where it starts in this case in Peru, but this
is
another subject. I.e., if it comes in at around a 45 degree angle instead
of vertical, it passes through the full 100% since it doesn't take the
straight path, and you are back to square one. These meteorite was
observed
to enter at an angle. Yes, I understand that "on average" meteorites
reaching sea level will go through more atmosphere, but this is a
non-issue
when they are conveniently sized and in free fall for that 3800 meters.
The
one effect I will agree that will cause a higher velocity, which has
nothing
to do with retaining cosmic velocity, is that FREE FALL VELOCITY is
greater
in thinner air. There is plenty to be said about that as you would
imagine
such as a potential doubling of the energy of impact making a bigger
crater
for something the size of Jilin. I don't think it is likely a huge ball
is
at the bottom of the crater. Just that there are plenty of kilos that
weren't pulverized in the mucky crater.
Best health,
Doug
The numbers behind the graph, I could post if you want, along with the
modeled temperature in F and C of the atmosphere over its lat/lon. I used
the trapazoidal rule to estimate the percent of the atmospheric mass with
the midpoints of intervals of 200 meters altitude for 0 - 25 kim above sea
level.), and considered that the atmosphere ended at 100Km above sea
level.
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