[meteorite-list] What makes a meteor glow?

From: Mexicodoug <mexicodoug_at_meteoritecentral.com>
Date: Tue, 29 Jun 2010 16:24:48 -0400
Message-ID: <8CCE5E03B122CD8-212C-379_at_webmail-d036.sysops.aol.com>

Bob wrote:
"how much an incoming meteor's light is due to heating of the material
itself versus the recombination of ionized atoms "

Hi Bob, List,

It seems important to me to consider whether it is the air heating the
meteoroid and not vice versa to pin down the origin of the bulk of the
glow=light energy. This question reminds me of the question: How much
of the heat of a car engine is from piston friction compared to that
resulting from the high pressure compression. (Aside: oil cooled or
ablation cooled, it is accepted that stony meteorites are usually
dropped cold and with no heat alteration inside).

Bob's question on the proportion of light from ionization vs. the
fraction of light from the meteoroid glowing like a light bulb filament
basking in its own heat stream seems a sticky question since there are
so many variables, velocity, angle, even shear strength and
composition. But a few observations ... first, most smoke (at least by
the time it is smoke) left by a meteoroid is not necessarily a source
of light so isn't an important contributor to the glow; and ablation in
this function isn't burning but more like wicking away some heat by a
meteoroid's equivalent of sweating, or just shedding/shearing away
friable fragments that have already been toasted/falling off upon
cooling/compression crack flakes, whatever...

I always thought the reason for a meteor glowing was mostly from the
"emissions by ions":

1) Meteoroid enters atmosphere fast
2) Atmosphere absorbs meteoroid's energy by compressing (squashing,
shocking, etc.) atmosphere in front
3) Great increase in pressure in front of meteoroid superheats that air
(like any compressor would)
4) Superheated air heats everything else it touches, including the
incoming meteoroid causing it
5) Superheated air can reach temperatures say, between 1500 and 6000
degrees C or so.
6) High temperature ionizes air (electrons in the air manage to absorb
some of the collisional energy)
7) When electrons (should I say ions to be safe...) relax or recombine
they emit the light (glow) in the visible and UV frequencies
8) The glow, or light, Bob asks about, I think is predominantly due to
the photon emitted upon relaxing energized ions.

Next, for a significant amount of the glow to be caused by "frictional"
heating (or just compression heating as above, it doesn't matter) we
would just need to look at what temperature is needed to glow white, or
at least not to be toooooo red, since too red is not the color of a
"typical" meteor. Red (black body) begins somewhere above 4400 C
degrees (Wien's Law) - so a typical baby ought to be a least a bit
hotter ... That is really going Solar and I think already hotter than
the "typical" observations, but someone else might know "if the fusion
surface sustain temperatures between 5000 C-10,000 C during the
incandescent path". But there is some rule of thumb used by re-entry
engineers saying the max. temperature reachable is the same as the
velocity in m/s. (10,000 K safety factor for 10 km/s) Confusing
enough...

But further we can wonder that in the "typical" meteoroid (meteor,
whatever) we don't usually see much of a change in color from the head
through the train (well, I know they have been known to change color,
but this is early vs late in the longer events if I am not mistaken,
not as a gradient in an instant of viewing(???). This would seem to
tell me that we are not seeing particles cooling down as I would expect
for a glowing space rock producing the light (blackbody cooling), but
rather an ionization-induced glowing and hardly any light due to the
high temperature of the object itself. Maybe the interpretation is all
wrong since intensity would play a roll and would just ask to some list
members with more experience in study of meteor spectra. But if the
train is basically the same color as the head, in those cases it is
hard for me to see too much heat from the glowing space rock being the
source of the glow or google it a bit, but I'd feel comfortable
imagining the dull orange-red color of space vehicle reentries and
maximum temperatures between 2000 - 4000 degrees in extreme cases.

What would be most interesting would be the posting of a total light
spectrum of a meteoroid that was incredibly imaged with the discrete
transition lines labeled for the popular ionic transitions and the
background black body sketched together in the same graph. Perhaps the
exact answer in such a given case to Bob's question lies in the
comparison of the area under the curve (lines vs. black body) of such a
spectrum assuming it exists...

Kindest wishes,
Doug




-----Original Message-----
From: Steve Schoner <schoner at mybluelight.com>
To: meteorite-list at meteoritecentral.com
Sent: Tue, Jun 29, 2010 11:06 am
Subject: Re: [meteorite-list] What makes a meteor glow?


I read somewhere that Nininger looked into that very question.
Somewhere in his
papers I think he reported that even a small meteor produces an ionized
trail
over a 1/4 mile in diameter.

Big fireballs, much larger.

Steve Schoner
www.petroslides.com
IMCA #4470


Message: 15
Date: Mon, 28 Jun 2010 15:09:17 -0500
From: Bob King <nightsky55 at gmail.com>
Subject: [meteorite-list] What makes a meteor glow?
To: meteorite-list at meteoritecentral.com
Message-ID:
<AANLkTimvxOx-WHnbVGThIyQ--O6LX1trnPc9_uSdllE6 at mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1

Hi everyone,
This thread has perhaps appeared before, but I can't seem to find a
clear answer on how much an incoming meteor's light is due to heating
of the material itself versus the recombination of ionized atoms that
have been heated by the object's movement through the air. I always
thought the majority portion -- the bright streak -- was a tube-like
glow of ionized air.
Thank you for your help on the question :)
Bob



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Received on Tue 29 Jun 2010 04:24:48 PM PDT