[meteorite-list] Tektites and Meteorites of Terrestrial Origin

[MexicoDoug at aol.com]

Rob M. wrote:

>Considering that there are readily identified
>meteorites from  two other large bodies on earth, I
>find it hard to believe that there are  none from
>Earth. The higher gravity and thicker atmosphere
>cannot  account for it all, surely. 
 
Large Bodies, my Lad!  Large Bodies, Indeed!  On the Moon, the  astronauts 
jumped tall buildings in a single bound...Granted, Mars, has a higher  gravity 
and thicker atmosphere, so let's forget about the  debilitatively beautiful 
Moon by comparison.  
 
Question:  Where on Earth would one need to be to duplicate the more  
favorable Martian conditions at Martian ground-zero for the successful meteorite  
ejections observed to have landed on Earth?  (Without even considering the  
possibility of meteorites from Olympus Mons at over thrice the height  of Everest?
 
Answer:  25 km high for atmosphere thickness and 3,950 km high for  gravity.
 
At 25 kilometers high on Earth we can match Martian surface pressure with  
our exponential drop off in pressure - though the drop off on Earth is somewhat  
more pronounced due to its being about 60% our scale height, I'm  thinking.  
To find the Gravitational point of reference corresponding to  Mars' surface 
on Earth we note that great Englishman's Universal law of  gravitation Mm/r2 
dependence.  The radius of Mars is:  53% of Earth,  and it's mass is 10.7% of 
Earth.  So (.107)/(.53*.53) is 38% at Mar's  surface.  To get to 38% earth's 
gravity with Earth's mass this changes to  1/(d2)=.38 =>d2=2.63=> thus d=1.62    
I.e., 62% of our  radius in height above earth's surface.  Our planet's radius 
is about 6370  km.  ===> You need to be 3,950 km high above earth to get to 
only 38% of  the gravity.
 
In conclusion, you might as well be comparing Jupiter to Earth as well as  
Earth to Mars.  Most meteorites don't really start to break up until below  25 
km, and even then, to make it into the envelope of survival, they need to  come 
in quite slowly.  As far as gravity, to equalize it you'd need to be  more 
than 10 times higher out into space than the International Space  Station!
 
You're right, atmosphere and gravity don't account for everything but they  
are pretty important laws for the survival of Earth's finest...not to be  
confused with the fining done to glass...
 
Saludos, Doug