[meteorite-list] ANOTHER QUESTION

[Chris Peterson]

Technically, fireballs virtually never hit the ground. But assuming that 
you mean fireballs produce meteorites, even that is hard to quantify. We 
assume, based on calculation and observation that many, or even most, 
meteorites fragmented from meteors bright enough to be called fireballs. 
But that doesn't mean most fireballs produce meteorites.

It is generally thought that in order to produce meteorites, meteors 
need to be slow and shallow. Also, they need to be large enough and 
sturdy enough that some material survives. Generally, meteorites 
represent only a tiny fraction of the original mass.

Different showers produce fireballs for different reasons. Leonids and 
Perseids are high velocity. When the particles are large (say, pea 
sized), they dissipate a lot of energy at high altitude. This means they 
burn up completely. Other showers, like the Geminids, are low velocity. 
Larger pieced can survive somewhat lower, and burn in denser air, for 
longer times. That's why Geminid trails tend to be longer than Leonid 
trails. But aside from questions about the material strength of shower 
material (assumed, but without much evidence, to be weak), most of the 
material is just too small to survive. It burns completely before it 
slows down enough to cool, and drop. There probably isn't much up there 
the size of basketballs, or even baseballs. I imagine comets produce 
some larger pieces like that, but they would only represent a tiny 
fraction of the total. It might be years between Earth collisions with 
such large pieces.

Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com


----- Original Message ----- 
From: <jwb7772 at netzero.net>
To: <meteorite-list at meteoritecentral.com>
Sent: Thursday, November 16, 2006 4:26 PM
Subject: [meteorite-list] ANOTHER QUESTION


Hi All!
     I have another question concerning meteor showers.  That is-----If 
showers do not produce meteorites, then how come fire balls are often 
seen during the Perseid's?  Fireballs often hit the ground providing 
that they do not blow up.  I believe that Temple replenished the field 
not too long ago so there has to be a lot of bigger rocks up there.  Yes 
most are just dust, rice sized grains and pea sized rocks but I like to 
think that base ball, foot ball, and basket ball sized rocks are just 
lurking around and just waiting for us to look up and watch them come 
screaming down in a blaze of glory!  Jim Balister