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Re: (meteorobs) Going by logic...
Hi Lew,
> Any proposed reason for this, Malcolm? Are slower heavy-object burnups
> actually likely to be BRIGHTER than fast ones for some reason? Or is there
> a preferred orbital plane and direction for heavier interplanetary debris,
> causing them to be more plentiful on the earth-catching than the
> earth-caught side?? Curious...
to my understanding it is the lower encounter velocity which causes higher
fireball rates in the evening hours.
Just a quick note for those who don't know the background: In the
morning hours we are sitting on the heading site of the Earth travelling
around the Sun. Thus, we have fast head-on collisions with the
meteoroids. In the evening hours, however, we are on the back side and
record only hits by meteoroids that wanted to pass us. Hence, their
relative velocity is slower.
Now: The faster a meteoroid enters the atmosphere, the earlier it will
burn up. Maybe it is because the particle gets destroyed completely
by the high pressure before it can start to ablate. A slow moving
meteoroid has the chance to decent deeper into the atmosphere and -
eventually - produce a nice fireball.
In fact, you need a very slow meteoroid to survive the descent and produce
a meteorite fall. I think the threshold is currently thought to be at ~20
km/s. All four so far recorded meteorite falls (Pribram, Lost City,
Innisfree, Peekskill) had initial velocities < 23 km/s (I hope I recall
the number right).
Sirko
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* Sirko Molau * __ *
* Verbindungsweg 7 * " 2B v 2B " *
* D-15366 Hoenow * *
* molau@informatik.rwth-aachendot de * Shakespeare *
* http://www.snafudot de/~smo * *
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