[meteorite-list] Meteorite from Jupiter-- uh, I mean TO Jupiter

[MexicoDoug at aol.com]

Chris wrote:

<<It is certainly possible to devise entry scenarios where  meteorites have 
unusually large velocities.>>
 
Hola Chris and Sterling,
 
You guys need to attach more numbers to these arguments imo with  sensitivity 
analysis.  Concretely, that meteorite in Darren's  picture-considering its 
shape-would be going about 47m/s (105mph), and not less  than 40 m/s (89mph) and 
not more than 60 m/s (134 mph).  The worst  case is the energy of a fast ball 
in the company baseball league, though  likelyhood is half that.
 
There are lots of ways to throw a fastball and bruise a grandma or loosen  
old plaster that your fingers can push through anyway.
 
_http://six.pairlist.net/pipermail/meteorite-list/2004-March/139871.html_ 
(http://six.pairlist.net/pipermail/meteorite-list/2004-March/139871.html) 
 
FYI here is a thread I posted to in Mar of 2004 on the subject of  speeds of 
falling meteorites.  I don't think there is all that much  uncertainty to the 
practical endpoints of how fast they can hit as terminal  velocity is reached 
easily in virtually all these cases, (the latter which Chris  has mentioned).  
 
I wouldn't hesitate to catch a baseball sized meteorite in the pocket of a  
baseball mit, though I am sure that that same falling rock would easily break  
someone's arm.  People can karate chop wood in half with bare  hands and the 
plaster of old homes can really be falling apart, how many of  us have put our 
hands through the wall on ocassion, so I don't see anything odd  with the 
results.  People who get punched get bruised all the time,  heck, some people get 
bruises on their butts from just sitting down.   Once the misconception is 
overcome that meteorites have retained cosmic  velocity it just becomes a 
question on how big the rock is and what it  hits.  An ordinary tale of sticks and 
stones and bones.  I was  carrying an iron in the back of my pickup and driving 
like a demon a while  back.  Didn't see a dip in the road and there was a rock 
in the back of my  truck.  When the truck was back on all fours again, the 
rock was still at  zero g, and now I have this great crater to show for it. They 
just don't  make the tinbed pickups like they used to...
 
Here's the calculations if you want to go through them.  A bowling  ball 
sized chondrite (11.25cm radius) weighs less than 23 kg and falls at about  291 
mph (130 m/s) (see prior post link provided above).  The terminal  velocity 
varies by the sqrt(mass)/sqrt(x-sectional area).  So for the  same material in a 
sphere mass increases with r^3 but cross sectional area with  r^2.  The 
dependence reduces to simply velocity being proportional to the  square root of the 
radius.  Thus a 50 gram sphere = 13.7 cc, r=1.49 cm  can fall at 36% of the 
bowling ball which gives the 47 m/s ball park you're  all in.  In that email I 
also checked the practical limits by  flattening it to a shield(3.3):(3.3):1 and 
orienting it in a 3:1 length:diameter  ratio and found that  the terminal 
velocity range was 90-130-211  (m/s), in other words 
69%(shield):100%(sphere):162%(oriented).  That's a  range of 1:2.35 from slowest to fastest.  Without 
messing with the radicals  since it is late, if we apply the same factors to the 
50 gram piece, we see the  speed range to hit the guy who though he was going 
fishing is 32.5 m/s (the  speed of a typical baseball fastball but only 30% the 
energy) on the low end and  76 m/s (a major league record fastball's energy) 
on the fast end.  The  energy difference is a theoretical factor of 5 
(76/32.5)^2.  But those are  the real extremes.  If we assume they are representing a 
couple of sigma  deviation, everything like the one in Darren's picture is in 
the  40 to 60 m/s range to bracket the 47 m/s. with reasonably a  double 
whammy packed in the fastest ones vs. slowest in this range.
 
Even after taking into consideration reasonable altitudes (Colorado has a  
somewhat thinner atmosphere causing the retention of a bit higher  terminal 
velocity...for example, than say New Orleans, and that 10 mph  seabreeze, the 
meteorite that hit that guy would have had a bit less than the  energy of a 
company baseball league fastball's energy.  And if it hits old  plaster will break 
some loose, and if it hits granny can break a bone and  definitely give a black 
and blue mark.  But if it hits Steve, the Jensens  or several other burly 
collectors out there on the shoulder blade it might  actually feel good even 
before they knew what hit them.
 
Saludos, Doug