[meteorite-list] Re: Crackpot Theory Redux

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Sun Oct 30 14:49:58 2005
Message-ID: <436523BC.AFF9BF17_at_bhil.com>

Hi, Axel, List,


    Hitting the atmosphere at very high speeds
generates a plasma of very high temperature.

    "Normal" re-entry plasma temps are 3000
degrees for carefully controlled orbital re-entry.
For the "normal" meteoroid re-entry, temps are
15,000 degrees (or more). For the high speed
particle, expect 50,000 to 200,000 degrees
within a millisecond.

    At these temperatures, the black body
spectrum contains major intensities in X-Ray
and even gamma frequencies. These very effectively
transfer the energy of the plasma to the body
of the particle.

    The result, within another few milliseconds,
is a cartoon noise: "Pfooot!" The "particle" is
gone. What remains is mostly slow-moving iron
ions, drifting away on the thin exosphere...

    The vast majority of cosmic rays are protons.
The big nuclei create a cascade of particle
transformations that end in a flurry of photons
and neutrinos. The most effective detectors for
high mass cosmic rays are flash detectors and
deep neutrino detectors.

    Interesting (to me, anyway) is the fact that
the heavy high speed nuclei have experienced so
much relativistic increase in mass that a nuclei
whose "weight" is a laughable concept will bulk up
until it weighs as much a good sized bacterium!

    Back to iron particles from supernovas:
The collapse of a star that masses many times
the mass of our Sun into a Type II supernova
takes place in less than a second! So the event
that creates the iron nuclei is effectively
instantaneous.

    The nuclei all have the same mass; they
all experience the same energy accelerating
them. So velocities are initially very uniform,
and the expanding shell of particles is very
thin and precise. Even after several light
years of travel the shells remain pretty well
defined.

    The density of iron particles encountered
depends entirely on the distance to the supernova.
Initially Knie and Hillebrandt guessimated the
supernova that produced "their" 60-Fe at 90 to
125 light years away. Then, refining the results,
they came up with about 75-90 light years away.
The more recent berylium-10 results suggest the
explosion was closer. Now, they are more cautious:
25 to 75 light years away.

    Since the density of particles depends on the
inverse square of the distance, cutting the estimate
from 125 light years away to 25 light years away
increases the density 25-fold! Big difference.

    You raise an interesting point about a heat
flash from re-entering particles at high density.
I don't think so, but it's like the chance that
the first atom bomb would set the atmosphere afire;
you wouldn't want to have to say, well, I didn't
think to check that...

    Every kilogram of material striking the
atmosphere at 40,000 m/sec (average for a
meteoroid) generates a specific heat
(proportional to temperature) of 194,134
calories. That's 8.12256656 ? 10^12 ergs.
At 400,000 m/sec, it's 100 times greater, or
8.12256656 ? 10^14 ergs. The surface area of
ONE SIDE of the Earth is 250,000,000 m^2.
So the average energy delivered is
3,000,000 ergs per m^2 per kg, at this
velocity, or about 1/2 of a joule.

    The Sun's flux is about 1400 joules
per m^2, so to equal the heat of Sun,
the event would require 2800 kilos
PER SQUARE METER impacting the atmosphere,
or more than a ton of iron particles per
square meter. This is unlikely many light
years from a supernova. (If you were closer,
you'd have other, bigger problems!)

    Big sigh of relief... On the other hand,
this calculation raises an interesting point
for meteoritics. The impact of a really big
object (100's of meters) would involve the
atmospheric impact (first) of billions of
kilos in a few thousand square meter area.

    Obviously, one could have an air-burst
impact that could produce a flash many, many
times the strength of sunlight, 10 to 100
times greater, as great as any nuclear weapon
would produce. This makes the reports of a
flash at Tunguska 40 kilometers away that was
strong enough to char clothing more likely
to be true (not that I doubted them). It just
explains them quantitatively.

    No, the iron particles don't get through
the atmosphere and ding up mammoth tusks with
little pits! The atoms of iron DO float down
and get deposited in sediments world-wide,
though, where they can be detected. From such
a recent event, the number of 60-Fe atoms should
be much higher than the numbers found in
Knie's 2.8 million year old sediments.

    The failure to find them would not invalidate
the rest of Firestone's isotopic anomalies, just
invalidate a supernova as the source. There are
other nasty energetic events to which the Earth
could have been exposed: a nearby short-duration
Gamma Ray Burst, a concentrated flux stream of
cosmic rays magnetically confined by the magnetic
field of our galaxy, a Type I supernova of a fast
passing star, or something we have never observed
yet.

    Isotopic anomalies such as he has discovered
require an energetic event in the neighborhood in
recent times. Period. End of story. Since this
represents an undefined and unexpected danger of
high magnitude, I, for one, would like to know What
The Xxxx it was. Only prudent, as the Elder Bush
used to say...

    Just because the neighborhood has been
quiet for a few thousand years, we can't
assume it always will be.



Sterling K. Webb
--------------------------------------------------
Axel Emmermann wrote:

> Thank you sterling,
>
> >>The division between objects that can reach
> >>the surface and those that can't
>
> I wasn't aware of this, very useful information. I'll remember that.
>
> But for the sake of discussion:
>
> 1) a supernova remnant crashes into its environment with speeds like 400.000
> miles per hour (I took Vela as an example, it's about 11.000 years old).
> Older ones may have slowed down a bit, younger ones may move faster, but
> after 11.000 years the initial pressure of the blast must have gone and
> inertia should be nearly the only source of motion.
> If the earth was to move through such a front the particles from it would
> NOT need 1.5 to 2 second for atmospheric passage. They would hit us at 180
> Km/s. Frictional heating begins at what?... 120 Km? That would reduce the
> travel time of a particle to a mere 0.6 seconds.
>
> 2) Cosmic rays are stopped by the atmosphere because there mass is roughly
> of the same magnitude as the mass of the air molecules. Somewhat heavier for
> iron nuclei or somewhat lighter for alpha particles but still differences
> are less than a factor of 10. They can shed their energy as "bremsthralung".
> Trillions of iron atoms would penetrate much deeper into the atmosphere,
> wouldn't they?
>
> 3) Fast traveling grains of dust may burn up in the atmosphere. Perhaps even
> at 180 Km/sec they might burn up before impact. But wouldn't the energy of
> those grains be converted to heat? More speed = more heat?
> If the earth was hit by a "sandblast" of a supernova remnant, how high would
> the particle density have to be in order to create a dangerous situation? I
> mean, if the sky is lit with a million pinpoints of matter that is heated to
> say a few ten thousands degrees, you may want to get a bottle of sun block
> FAST ;-))) I can imagine a sky that is so hot that it sets organic matter
> ablaze in milliseconds.
> That would effectively wipe out any life form that is too large to be in the
> shade when things got rough... Mammoths, bison...
>
> Would this be realistic or am I dreaming? ;-)))
>
> Axel
>
> -----Oorspronkelijk bericht-----
> Van: Sterling K. Webb [mailto:kelly_at_bhil.com]
> Verzonden: zondag 30 oktober 2005 2:05
> Aan: Axel Emmermann; Meteorite List
> Onderwerp: Re: [meteorite-list] Re: Crackpot Theory Redux
>
> Hi, Axel,
>
> The dynamics of the situation are such
> that increasing the speed of an incoming object
> in an attempt to penetrate the atmosphere
> without losing all its mass to frictional
> ablation just never happens for small objects.
>
> Now, a big object, like a 1000 meter
> asteroid will ALWAYS penetrate the atmosphere
> and reach the surface of the Earth; and a small
> object, like a 1 mm grain, will NEVER reach the
> Earth's surface at speed (it might float down;
> see below). In both cases, this is regardless
> of initial speed.
>
> The division between objects that can reach
> the surface and those that can't is this: if the
> mass of atmosphere in the path of the object is
> greater than the object's mass, it won't make it;
> and if it's less, it will. Speed doesn't enter
> the equation (much).
>
> Imagine a 1 mm grain; then imagine a 1 mm
> "tube" of atmosphere extending from the top of
> the atmosphere to the surface. If that "tube"
> contains more mass of atmosphere than the mass
> of the grain, the grain won't be able to reach
> the surface.
>
> Such small grains, at "normal" entry
> velocities, will be stopped without frictional
> heating and just float down to the surface.
> This is how most interplanetary and interstellar
> dust arrives at the surface and becomes incor-
> porated in sediments, many 1000's of tons per
> year. At high entry velocities, small grains
> burn up completely.
>
> Firestone's belief that because iron grains
> are formed in the heart of a supernova, they could
> survive re-entry is completely mistaken. The
> individual iron atoms are created in the supernova
> and accelerated to immense velocities in nano-
> seconds. That does not matter; you can't destroy
> an individual atom. They assemble as grains when
> the atoms are crowded together under high pressures
> and temperatures in their first few milliseconds.
> But assemblages of trillions of atoms, like tiny
> grains, can be dis-assembled. When that happens,
> the individual atoms are not destroyed (they float
> down), but they're not particles any more...
>
> The heating depends on the ratio of particle
> surface to particle mass, which is high for small
> particles and low for large particles. So, for
> a very large object (100's of meters), it just
> can't be vaporized fast enough to be stopped in
> the 1.5 to 2.0 seconds of atmospheric passage!
> The kind of objects that produce meteorites (10's
> of meters) lose 90% or more of their mass before
> fragmenting and depositing the pieces as meteorites.
>
> An obvious demonstration of the fact that speed
> alone will not get you through the atmosphere is
> the example of very energetic "cosmic rays," like
> an iron nucleus travelling at 99.999999999% of the
> speed of light: very small particle, very high
> speed, but such cosmic rays are nicely stopped by
> the atoms of the Earth's atmosphere. (To be
> completely accurate here, 1 such particle in
> 10^24th particles will pass right through the
> atmosphere and the Earth itself and be detected
> as a vertically rising "cosmic ray" on the other
> side of the Earth! But, that's because of its
> small nuclear dimension, and as you can see,
> it's rare...)
>
> Sterling K. Webb
> ------------------------------------------------
> Axel Emmermann wrote:
>
> > Hello list,
> >
> > I usually lurk from behind the Atlantic but his thing has captured my
> > imagination.
> >
> > Most of you are likely to have more background in astronomy and physics
> than
> > I have, so I'll put it to you as a question:
> >
> > What would happen if little drops of iron smash into the atmosphere at
> such
> > a velocity that the time they need to reach the surface is smaller than
> the
> > time to heat them up through and through?
> >
> > Heat has to travel to the inside of such a pellet in order to evaporate
> it,
> > doesn't it?
> > Conducting heat to the core of a meteorite must be function of its
> > composition, so iron will be hot fast but iron mixed with dust will take a
> > lot longer. But still, evaporating a meteorite would still be a process
> > which needs a finite amount of time, right?
> > Now, if the meteorite's journey through the atmosphere is shorter than the
> > time needed to heat it to evaporation from say -150? it would hit the
> > earth's surface, or not?
> >
> > Another thing perhaps: isn't it possible that at VERY high speeds an
> > impacting object just compresses the air in front of it and is actually
> > protected by this cushion of supercompressed gases?
> >
> > Axel
> >
Received on Sun 30 Oct 2005 02:49:16 PM PST