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

From: MexicoDoug_at_aol.com <MexicoDoug_at_meteoritecentral.com>
Date: Thu Jun 22 03:26:42 2006
Message-ID: <325.6648ca4.31cba00f_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
 
Received on Thu 22 Jun 2006 03:26:07 AM PDT