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

From: Chris Peterson <clp_at_meteoritecentral.com>
Date: Thu Jun 22 10:39:40 2006
Message-ID: <00ce01c69609$993b24e0$fd01a8c0_at_bellatrix>

Hola Doug-

My earlier response to Pete had numbers attached: a 50 g stone suggests a 30
mm diameter and a terminal velocity of 50 m/s (I assumed a sea level fall).
Not having viewed the stone in question, I simply assumed it was spherical,
hence there was no speed range given. I'm happy to see we've arrived at
about the same numbers- ain't math grand?

All the same, it is possible, albeit extremely rare, for a small object to
arrive at the ground significantly above terminal velocity. However, such
scenarios would seem pretty much to require the low altitude fragmentation
of a much larger body, ala Sikhote-Alin. It's hard to imagine such an event
could occur without attracting a good deal of attention, so I think we can
pretty safely conclude (for reasons other than the obvious statistics) that
an isolated fall of a 50 g meteorite, or even the somewhat larger
Wethersfield falls, occurred at anything other than the expected terminal
velocity.

Sterling commented that all falls are different. But really, I think they
are actually quite similar in most cases; what is different are the last
second dynamics dependent on just what they actually fall on.
Chris

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


----- Original Message -----
From: <MexicoDoug_at_aol.com>
To: <meteorite-list_at_meteoritecentral.com>
Sent: Thursday, June 22, 2006 1:26 AM
Subject: Re: [meteorite-list] Meteorite from Jupiter-- uh, I mean TO Jupiter


> 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 10:38:59 AM PDT