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Re: (meteorobs) P/2000 G1 & Vgeo


>Stony meteoroids are more similar to iron than to cometary meteoroids
>in terms of mechanical strength of the material. They do not break up
>so easily and are in this way more similar to iron meteoroids. If this
>is indeed so, then this indicates that the major factor determining the 
>brightness of the meteor is the surface area and not the thermal
>conductivity of the meteoroid?

Apologies for coming into this thread near the end, folks. (How did I
miss the messages leading up to Jure's? Oh, well, we're a busy list!)

Again, I know I'm talking based purely on hearsay, but the conventional
wisdom I've always understood is that meteor luminosity, and therefore
magnitude, is much more significantly dependent on Vg (recall a recent
thread where THAT was discussed), than on any property inherent in the
meteoroid body itself. (Keep in mind where all the energy input for the
meteor phenomenon is coming from: KE = 1/2 m v^2.)

This is because (so I've always understood), the bulk of visible light
from the "meteor" phenomenon is actually a result of atmospheric ioniz-
ation caused by the direct conversion of Kinetic Energy into radiation.
(I'm not sure how much of the radiation itself is in visible light, nor
if it's truly negligible or just a lesser partner in meteor brightness.)

Thus if two meteoroids strike the atmosphere, one at 11 km/s while the
other is going 72 km/s (the minimum and maximum for solar-system bodies),
the brightness difference between the two should be very predictable, ir-
regardless whether one's iron and the other cometary dust-bunny, one flat
and the other conical, one 20 cm across and the other 5 cm across, etc.

That being said, I also recall something which might seem to contradict
this conventional wisdom somewhat: namely, that "terminal bursts" often
seen at the end of a fireball track are the result of the fragmentation
of the meteoroid - suddenly creating much more SURFACE AREA, and there-
fore markedly increasing the efficiency of KE-radiation conversion. So
it must be the case that meteoroid shape (and also composite shape and
binding) plays more of a role than the simple 1/2mv^2 picture indicates.

However, that said, it's hard to see how the thermal conductivity of the
meteoroid body would much affect the all-important rate of conversion of
kinetic E to radiation: Am I (and my conventional wisdom) way off here?


Clear skies, and thanks for yet another interesting theoretical thread!

Lew Gramer


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