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Re: (meteorobs) meteorites from Geminids?


Hello,

Interresting point raised indeed! Never thought about this before.... I
guess it depends on whether the stream has particles large enough, and a
few other things. There has also been some suggestion that Phaeton is a
dormant comet (which might suggest it does not have particles large enough).
Anyhow, given the mass segregation in the stream (the larger particles move
in wider orbits and encounter the Earth orbit at a different point than the
smaller ones, i.e., the larger particles appear later in time. This is well
known to many of us of course: the brightest Geminids always after
maximum!), best changes would be after maximum.

Our Dutch photographic results show a clear relation between meteor
brightness of Geminids and the altitude of extinction. This perhaps could
be a measure of how bright a Geminid should be to make it penetrate deep
enough for possible survival of remnants. Meteoritic fireballs usually get
extinct at about 20 km altitude. From the brightness/penetration dependance
of our photographic data (note: with a very deep extrapolation!!) this
suggests that a Geminid should be brighter than -12 to let it penetrate to
the depth of a typical meteorite dropper. Whether it really does drop a
meteorite is, of course, also determined by other things.

One thing is not so favourable: the meteoroid speeds in the Geminid stream.
Meteorites usually have entry velocities below 30 km/s. Geminids have an
entry velocity of about 35 km/s, which might be too high. They could be
'crushed' when penetrating deeper into the more dense parts of the
atmosphere at 30-40 km altitude. In that sense, the brightness/penetration
dependance mentioned might not be valid for lower altitudes (our data ends
at about 50 km altitude, where Geminids in the -5 to -3 range enxtinguish).


-Marco Langbroek
 Dutch Meteor Society





At 00:55 1998-08-18 -0400, you wrote:
>>And by the way, this leads to a question of my own! Isn't there at least 
>>the THEORETICAL possibility that one particular shower, the Geminids, 
>>might drop a meteorite, since they derive from an asteroid?
>>
>I have always asked myself the same question Lew! Very intriguing.
>>
>>Now what was your *second* question, Pierre??
>>
>Uh oh..dot it escaped my mind for now. Must be because its finally time for
>a long night of sleep.
>
>>Clear skies,
>>Lew
>
>
>                                .    .    . .
>Pierre Martin                  . . *  . *  .  .
>***************************** . . . \   | .  .
>Ottawa Valley Observers Group  .  .    .  .   . .
>Visual meteor observer          .    . . .  -* .
>Ottawa, Ontario, CAN              . .   . .  .
>home:  p.martin@cyberusdot ca           /  . .  . .
>*****************************       *  .   .  .
>Graphic Designer                     .  |    .
>National Aviation Museum                |   \
>work:  pmartin@nmstcdot ca                 *  . \
>*****************************                 \
>                                               *
>                                     
>
>
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