[meteorite-list] Re: Tektites II (PART ONE)
From: meteorites_at_space.com <meteorites_at_meteoritecentral.com>
Date: Thu Apr 22 09:43:32 2004
Even though I attempted to edit out some of Kelly's
confusing WEBB 1' and 2's it is still much larger than it should have been. (It was not all that confusing in the first place)
I will be in two parts.
Re: Tektites II (PART ONE)
Re: Tektites II (Part TWO)
On Sun, 15 July 2001, Kelly Webb wrote:
> Hi, Steve and List,
> This is my reply to Steve's reply to my reply to Steve's... Wow, way
> too many levels of recursion here. OK, we're going to go to the triple
> interleaved posting format: my former posting (with >'s), Steve's
> replies, and my replies to his replies. To help keep the sequence of the
> three different texts straight, I have added the "speaker's" name to
> each level respectively (WEBB1, SCHONER, WEBB2).
> Got that? You can't tell the players without a program...
> All spelling (typing) errors are mine (except for the ones that are
> Steve's). All other errors are for the reader to judge.
"WEBB2" and "SCHONER" notations have made it much more complicated than it should be, In order to get this posted, under the 40 K I have had to divide it into two parts.
My rebut is after the "SRS>"
> Whatever it was it was fragile. And having fallen on June 30th, and in
> the morning, it might have been related to the Taurid (?) meteoroid
> stream that the Earth passes through at around that time. I am not sure
> if it has been correlated with a comet or an asteroid. But it does
> seem coincidental that it fell at that date, and during a time of each
> year when large fireballs are likely to be seen.
> Not fragile (see below). 200 bars crushing pressure (3000 pounds per
> square inch) are calculated for the Tunguska Object based on the air
> density at the altitude of its airburst and a "reasonable" assumption
> for its velocity.
> I too agree it was probably a beta Taurid, a daylight meteor stream
> and one of two streams associated with the decaying Comet Enke.
> Personally, I'm certain it was. Well, as certain as I get. Just wait
> until 2042 AD when Ken Brecher's Canterbury Swarm is supposed to come
> back (or not, depending on whether it really exists). I believe in the
> beta Taurids for the simplest of reasons: witnessing a daylight fireball
> half as bright at the sun itself over 30 years ago (on a June 29th).
> It's one thing to read about big potential impactors; it's another thing
> to stand there with your mouth open watching hundreds of secondary
> shadows swing around in unison as one passes overhead. It impressed the
> hell out of me.
> Hey, did we just agree on something?!
Yes, we agree on this. The question though is how fragile are comets
that break up well before entering the Earth's atmosphere, and how
they will behave once they do.
> And we don't know what the effect of impacts to their structure and
> composition will be either. I would assume that they would, because
> they have been hit, and are being hit by other cosmic debris, that their
> composition would reflect that. But more importantly, how will such
> impacts while they are out in space affect the cometary structure? How
> fragile will they be after all of that bombardment? And how will they
> stay together when the do enter a planet's atmosphere?
> Questions not easy to answer.
> What we do know is that some comets are very fragile, and they break up
> by Solar wind pressure alone.
> Their fragility, composition, fragmentation are all irrelevant in
> that short dash through the atmosphere at cosmic velocities. I'm going
> to quote you a source here, since I perceive some reluctance to take my
> word for it (don't blame you; I'm the same way).
> I looked in Rocks From Space and other common sources but discovered
> none of these books spell it out the physics of it very clearly.
> From John S. Lewis, Physics and Chemistry of the Solar System,
> Chapter VIII, Meteorites and Asteroids, p. 309ff:
> "Often, small bodies will be decelerated to subsonic speed before
> reaching the ground. About the largest body that could possibily reach
> the ground in one piece, without exploding on impact, would be a
> monolithic chunk of iron, preferably extremely flattened, travelling at
> the lowest possible entry speed, and entering the atmosphere at a very
> shallow grazing angle. The limiting size can be calculated to lie in the
> range of 30 to 100 tons..." (Webb: About the size of the Hoba meteorite,
> you'll note.)
> "For a spherical stone, roughly 3 m in diameter (40 ton) for a
> density of 3 gm/cm^2 is the upper limit..."
> "Fragmentation is unimportant for very large impactors, irrespective
> of size, because the fragments of large bodies do not have time to get
> away from each other before impact with the surface... For a typical
> stone, the critical size (for ignoring fragmentation) is about 300
> meters. Deceleration is important for entering objects only if their
> mass per unit area (essentially pd3/d2 or pd) is less than that of the
> atmosphere above the Earth's surface."
> Webb: Picture it this way. The atmospheric pressure is about 1 kilo
> per cm^2. That means that a mass of 1 kg of air sits on each square cm
> of the surface. Imagine that our incoming meteorites are, oddly enough,
> perfect cubes. For a one centimeter cube to make it through the
> atmosphere without slowing down much, it would have to weigh 1000 grams,
> a very high specific density of 1000.
> But a 10 cm cube would have to weigh 100 kilos, but its specific
> density would only be 100 (100,000 grams / 1000 cm^2). A one meter cube
> would have to weight 1,000,000 kilos, but its specific density would
> only be 10 (10,000,000 grams / 1,000,000 cm^2). I think you can see the
> trend here.
> A ten meter cube would only have to be as dense as ice (specific
> density = 1), a 100 meter cube 1/10 as dense as water, a one kilometer
> cube 1/100th as dense as water, a 10 kilometer cube only 1/1000, and so
> forth. At this point, our impactor is less dense than air, which raises
> other severe problems.
All the facts and figures aside, it seems you still cannot grasp the fact
that the air at 10 to 20 miles up is sufficiently dense to cause a hypersonic
cometary mass to produce it's crater in the air (Tunguska event) rather
than on the ground. Russian researchers came to this conclusion in
their examination of the effects of the Tunguska bolide. If you want
I could go and find the entire manuscript and post it for your examination
as well as edification.
The breakup was not like a gradual fragmentation, caused by dynamic
atmospheric disruption, but an almost instantaneous blast produced as
the meteoroid pulverized itself in the atmosphere. But it was more than
a simple pulverization. The energy release as the particles came to a
virtually abrupt stop released as much energy in the air as it would have
had it survived intact to the ground.
The rationale behind this dynamic is clear. All the mathematics you
can provide cannot dispute the fact that the Tunguska event was in
fact a cratering event in the air. And that is why there was not a crater
produced on the ground.
> > The weakest fireball objects burst at 0.1 bar, so obviously there
> >weak and fluffy material out there, corresponding to interplanetary
> >with densities of 0.01 to 0.10 gm/cm^3. However, your assertion that a
> >10 kilometer weak'n'fluff would never reach the surface of the Earth
> >well, ridiculous. The factor in determining whether an object will
> >suffer ANY decceleration in the atmosphere depends on the total mass
> >unit area of frontal surface of the object.
> Maybe my assumption might seem ridiculous to you, but it is obvious that
> such may very well have happened as the tektites indicate. Impact (or
> impactor) products (tektites and microtektites) scattered over areas as
> broad as 10% or more of the Earth's surface and-- not a trace of a
> And these strewnfield distrubutions cannot be supported by having been
> formed, and ejected from the moon to Earth?
> Humm... being skeptical... something is wrong in this picture.
> However, there are several tektite fields that do seem to be associated
> with known craters, The Ivory Coast tektites-- Bosumtui (sp),
> Moldivites-- Reis, and Georgia tektites-- Chesapeake Bay crater.
> But the Indochinites are the most enigmatic, for they point to some type
> of atmopheric bursting event that liberated enough heat to vaproize the
> impactor as well as ground rocks, throwing them far and wide of the
> epicenter of the event.
> > Once an object is big enough to have more than 1.057 kilgrams of
> >mass for every cm^2 of frontal area, it's gonna reach the surface of
> >Earth with its cosmic velocity relatively undiminished. The dynamics of
> >cometary impact are as well known as that of any other kind of impact.
> >That 10 kilometer fluffball of yours is just as deadly a hazard as any
> >other object with its mass and velocity, whether stone, iron or pure
> >neutronium [kinetic energy = mass x (velocity)^2]. A cometary fluffball
> >with the density of interplanet dust particles, if there were such a
> >thing, would reach enough mass to punch through essentially unimpeded
> >the 500 meter size.
> I do not dispute that objects of the size that produced tektites are
> cosmic hazards to the Earth. Tektites clearly demonstrate that. But
> the fact is that, if they were, as I am convinced that they are,
> terrestrial, and no crater exists then an atmospheric burst (Tunguska
> event) must be the culprit. And though I don't dispute your
> mathematical reasoning, you have not proved that such a "fluff ball"
> (such as are some comets that break up by Solar Wind alone) ABSOLUTELY,
> and without question MUST reach the Earth's surface even if its size be
> at or below 10 Km in diameter. I suspect that there are other factors to
> be considered, such as the angle of entry, the velocity of the impactor,
> as well as its composition.
> The question really is, how fluffy can the fluffball get and hold
> itself together as an object. A density of 1/100th of water is out of
> the question. That is the density of a Brownlee particle 10 microns
> across. Brownlee particles are that size because that represents the
> maximum size an object that "fluffy" can get. But Brownlee particles are
> soot-like mineral oxides from which the volatiles have escaped. They are
> found floating in the upper atmosphere and, although cometary in origin,
> they cannot be a model for a low-density comet
> I don't know where you got the idea of comets "broken apart" by the
> solar wind.
> I've been through every book on comets I've got handy
> (Yeomanns, Delsemme, etc.) with lots of material on solar wind
> interaction with cometary ion tails, etc., but have yet to encounter any
> such instance of "breakup" cited or suggested. I doubt the idea, but I'd
> like to know if you have a specific source.
Oh really!... Check out www.spaceweather.com, and follow all of the links
regarding Comet Linear C/2000 A2, shining in the eastern morning skies at
this very moment.. It broke up under the influence of solar wind
pressure, and radiation. Comet Kehotek (sp) did the same, and I
watched it do so when I was working at Lowell Observatory in 1974. Then
there is Biela's Comet in 1882, it broke up into at least 6 discrete parts
on its first witnessed passage of the Sun and evaporated afterwards,
probably breaking up into hundreds if not thousands of tiny pieces.
Then look at the Comet Shoemaker-Levy impacting Jupiter. Granted the
gravitational forces played a major part in the breakup, but the fact
proved is that comets are fragile-- irrespective of their mass.
And let's examine some of the chains of craters found on the Moon, and
Mars, as well as other moons in Solar system. I remember reading recently,
and after Comet Shoemaker-Levy's impact of Jupiter that such chains
might very well have been produced by fragmenting comets.
And I am sure if I look it up that there are many other instances of
comets being seen to break up in space as they approach the Sun.
IN FACT-- the "M" class comets, the so called "Sun Grazers" (they all
follow the same orbit) are thought to be fragments of a mega-comet that
broke up on its first approach of the Sun 10, maybe 15,000 years ago.
So, if you look you will see that there is more than enough evidence to
indicate comets can indeed break up as they enter denser fast moving streams
of Solar wind and pressure. What do you think causes them to have sweeping
tails of gas and dust that streams as far as 100 million or more miles
behind them? For a comet, solar wind and radiant energy are destructive
> At any rate, in a fluffball the size you suggest the tidal forces
> (differential force of solar gravity between the near and far sides of
> the object) are more than enough to rip the fluffball to shreds unless
> it has sufficient structural strength to resist. At the size you are
> talking about, the object would also have to resist crushing by its own
> gravity. Your fluffballs have to be able to survive in their own free
> orbits for long periods. I won't even go into another mystery, how such
> a critter might form in the first place.
First off, "fluff balls" is perhaps a bad choice of words.
Comets are not "fluff balls" like the "dust bunnies" that one is apt to
find underneath one's bed. Instead they are probably chunks of gas and
water ice with some degree of porosity. They are most certainly less
substantial then say an asteroid. And more importantly, comets are
not what you say I said and continue to say what they are.
I DID NOT, and I repeat DID NOT say that they are anywhere as
insubstantial as you are claiming that I said they are..
You have created a "straw man" and are running with it. Cometary
material in the nucleus is not a vacuum, nor so insubstantial as
you are saying. Fluff balls was a bad choice of words, and I now
admit that seeing where you have gone with the phrase. But the
fact is that comets are probably solid ice with possibly a trace or
measurable quantities of dust scattered within. How "solid" this
mixture is is the question. And I think that because they can
break up under the influence of Solar wind and radiant energy is
a clear indication that the ones that do are much, much more fragile
than the asteroids.
Sorry if I seem a bit ticked off here, but please don't put words down
that I did not write, and then knock them down as if they were mine.
That is an easy way to prove one's point, but not to disprove the
actual point made.
> Some years ago, I saw a very interesting abstract by a Russian
> researcher looking into the dynamics of the bolide that created the
> Tunguska event. His analysis of it, using computer and mathematical
> models incorporating data gleaned from hydrogen bomb tests produced very
> interesting results. As the impactor broke up, according to him, it had
> a "cascade effect" In other words the breakup caused more break up, and
> it progressed exponentially in the span of a millisecond or less, so that
> the energy release was as equal to that of a hydrogen bomb explosion in
> the air(airburst), not only in energy release but in effect as well.
> The key point in his analysis as I remember was the total energy
> released in relation to the time element of the release, and the medium
> (air) in which that energy was released.
> His conclusion was that the impactor made a "crater" in the Earth's
> atmosphere rather than the ground. Though not a very large body, if this
> was so then impactors do not have to reach the ground to produce
> craters. "Craters in the air" is what can be produced by an impactor if
> the conditions are right.
> IN the case of tektites, they are evidence of such events on a much,
> much larger scale than the 1908 Tunguska event.
> Of course, that is exactly how airbursts happen. No one doubts that
> or has suggested anything else. We can all agree to your craters in the
> air. But how big can they be?
Certainly larger than 100 km. Air moves faster, and more easily than
solid rock. Air is much easier moved than rock, so I would conjecture
that the crater would be significantly larger.
> > Ignoring the numerical coefficients, we have a factor here composed
> > >of density x diameter^3 / diameter^2. This reduces to density x
> >diameter. Even a little simple arithmetic would have revealed that your
> >fluffball would have a volume of 5 x 10^29 cm^3 and a frontal area of 8
> >x 10^11 cm^2 and hence would have to have a density of less than 10^-13
> >gm/cm^3 to be unable to penetrate the atmosphere, or in other words, a
> >density essentially similar to space itself or a very good laboratory
> >vacuum. So, in a way, you're right: balls of vacuum do not penetrate
> the atmosphere!
> NO, NO, NO! I think you had better go back to the drawing board on that
> one. A cometary "fluff ball" does not mean a vacuum.
> My point is that your fluffballs in the size you're talking about,
> in order to not reach the ground but aurburst instead, would have to
> be virtually a vacuum or at the least an "airball." Refer to the
> step-by-step density reduction in my previous comment.
When I said "fluff ball", as I stated previously meant something quite
different from what you have said in the above.
Your step-by-step density reduction argument is faulty. It has assumptions
that do not take into account the obvious physical nature of comets. Nor
do they take into consideration the fact an object such as a comet moving
at hypersonic velocity will respond in the same way than a much more solid
body such as an asteroid will respond given the same speed and angle of
attack. I do not confess to be a physicist or a mathematician such as
yourself-- However-- I do see that your assumptions lack certain elements
that are required to explain obvious facts.
That is Tunguska events, and also the possibility based on the physical
evidence that mega Tunguska events can, and do occur-- as the presence of
the tektites attest. Your calculations need to incorporate a factor that
allows for the structure of comets-- like the comets that
DO BREAK UP in space and by light, and Solar wind pressure alone
(Comet Linear now bright in the eastern sky)
> The analogy of bullets and targets is a very poor one. Cosmic
> velocities are orders of magnitudes greater than what's produced by
> human popguns. Kinetic energy goes up as the square of the velocity. The
> kinetic energy of the fastest bullet is only great enough to deform or
> shatter it. A gram of material moving at 72 km/sec, the highest possible
> intercept velocity at the Earth's orbital distance, has 1000 times more
> kinetic energy per gram than the energy released by the explosion of a
> gram of the most powerful chemical explosive known. In fact, when this
> amount of kinetic energy per gram is released in an impact, less than
> 0.2% is used up vaporizing the impactor; the rest goes into the force of
> the explosion. We measure the impact energy in tons of TNT equivalent,
> but a one-ton body moving at this speed has more kinetic energy than the
> ton of TNT has explosive energy, by a thousand-fold!
RIGHT! But the analogy of solid versus "stinger" rounds still holds up.
Now use the above to consider that under certain conditions the
atmospheric pressure will disrupt a fragile body just as solid rock would
a much, much more solid one. In this regard, there is another factor that
you have not considered, how transparent are comets to infrared radiation?
That is if they are entering the Earth's atmosphere at hypersonic speed
the superheated air cap in front of them will also produce enormous amounts
of infrared energy. In ice or fairly transparent solids, as I feel
confident that most comets are, how deeply will that energy penetrate
into the comet itself? What will be the effects as this energy then
heats up the deeper layers and the dust particles within?
I think that under these conditions the comet in question would rapidly
disrupt, it will explode in a cascade reaction-- Just as the Russian
physicists studying the Tunguska event concluded. And this is true for
even the large comets, say up to and including 10 km. So again, as I point
out above-- just because a cosmic body has such and such a mass DOES NOT
mean that when it hits our atmosphere it will also hit the ground.
The nature of the object in question may introduce factors into your
equations that preclude that.
Tunguska events happen...
Back to the drawing board for you...
> The point here is that kinetics on this energy level is, in fact,
> totally unlike conventional earthly events, like bullets. Composition
> matters little. Density shades the results (an iron can be a little
> smaller than a stone and an ice can be a little bigger), but doesn't
> affect the outcome much. Composition affects the outcome less and less
> as the impactor gets bigger and bigger.
> (It's difficult to realize how potent kinetic energy alone can be. A
> gram of anything moving at 7000 km/sec would have more kinetic energy
> than the energy produced by the nuclear fission of one gram of
> plutonium. In other words, shooting a chunk of rock at a planet at this
> speed would be just as effective as a nuclear bomb with the same weight
> in fissionables. At this speed, a one kilogram rock would equal the
> Hiroshima bomb in energy release!)
Right-- But as I previously stated, the structure of the impactor in
question will also determine how that energy and where in the atmosphere
or the ground that that energy will be released. As it is traveling
through the atmosphere at hypersonic speed it is still acting in the
realm of Newtonian physics. It is expending its enormous energy all
along its path emitting it in the form of electromagnetic radiation,
and or heat. BUT as soon as it hits something at cosmic speed ALL of
the remaining energy is converted to heat-- instant vaporization of the
target, and the projectile. The law of conservation of energy is in full
play and KABOOM-- an explosion equal to and perhaps many, many times
exceeding that of a thermonuclear device is the result.
When does the particle stop?
Even if the "particle" in question is a very friable comet of substantial
mass-- does it have to stop only when it hits the ground? That is the
question that you seem to be missing (or dismissing).
When I watched the Great Leonid Fireball shower of 1998, I was astonished
at the number of fireballs created by supposed cometary particles. I watched
them shoot across the sky, fast and graceful. And many of them exploded
brightly in a terminal flash. Nothing proceeded on after that, and the
light from them was on the order of magnitudes greater than their brilliance
as they traversed the sky.
Then at the break of dawn as a finale a bright Leonid appeared shooting down
toward the eastern horizon at great speed. Its terminal blast was so
great that it lit up the landscape bright as day, and the whole sky lost
its stars in its brilliance. This terminal blast I understand occurred at
an attitude of 20 to 30 miles. And the particle that created it was probably
a chunk of cometary ice no larger than a walnut. BUT it came to a complete
stop at 20 to 30 miles up. ( I know this because I got several reports from
around the state and from that with a bit of trig, I was able to estimate
HOW much air is up there at 20 to 30 miles?
Enough to stop a particle the size of a walnut traveling at 66,000 mph dead in
its tracks causing it to expend all of its kinetic energy in a terminal blast!
Now, prove mathematically that a very fragile, but a full sized comet
significantly larger on the order of many, many magnitudes larger could not do
the same if the angle of entry was right.
Tunguska proves that such can happen, and with as you say objects most likely
much denser than comets
GO TO PART 2
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Received on Tue 17 Jul 2001 09:47:39 PM PDT