[meteorite-list] British Study Attempts to Calculate Odds ofBeing Hit By a Meteorite

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Mon Jul 31 04:59:09 2006
Message-ID: <00ef01c6b47f$932109a0$64704b44_at_ATARIENGINE>

Hi,

    I think that, by the indicated weights, they are referring to
the mass of the object to reach the ground at speed. You will
note that they say of the eight 25 pounders "if they landed," but
the vast majority never would.
    As for the one-tonner, I used the Impact Calculator of
puzzling performance and could never get a one-tonner to
get to the ground and the best I could do is get "some large
fragments" to the ground at very high velocities-- 7 miles/sec
up to truly cosmic velocities. The 1 to 4 tonners all airburst
at 150,000 to 200,000 feet up.
    The impact calculator doesn't calculate the effects of a
stone "fragment" hitting at 7 to 15 miles/sec! Lots of nasty
craters and explosive events you'd want to avoid there,
I'm thinking.
    If the one-tonner is 1/4 of a four-tonner and is going to
hit at escape velocity or above, I don't think I'd want to be
in its little 133-acre patch! Could I have a bleacher seat
about 3, no, 5 kilometers away and a video camera, please?
    That's for common stones. Irons are a different story.
I had no trouble getting a one-ton iron to the ground with
an impact energy release of 2600 pounds of TNT, hitting
at 500 mph. How close do you want to be to that? A 133
acre circle means that you couldn't get further than about
650 feet away from the center of the impact zone. There's
a 20 foot crater there, BTW, and 100-150 tons of ejecta
flying out of there, at 300-400 mph.
    Speeding the iron up to high velocities only increases
the force of impact to about 6 tons of TNT and a 40 foot
crater 10 feet deep when it hits at Mach 2. Still no place
to be loitering and lounging about -- you'll be busy dodging
ejecta -- 600 tons of it.
    Meteorites -- that's the survivors -- make very soft
landings. That's why they're survivors, and that's why they're
rare. There's something decidedly ODD about them -- they
get to the ground intact. No craters. No explosions. Like
my favorite example NOBLESVILLE -- just a Whirr! Thunk!
    Most do it through fragmentation, stagnation, and airdrop
at atmospheric terminal velocity and at most a dent in the
Norwegian (or other) garden. They're the ODD ones.
    There's no trace of a "crater" nor any physical damage at
the site of HOBA -- 60 tons of iron now, and probably 100
tons when it "nestled down" so gently. That's really ODD.
    I like the "cross-section" method I posted here back in
2000. We're up to about 1-2 likely car impacts per decade
now. People are a much smaller target but somewhat more
numerous than cars. I make it even odds that someone,
somewhere will get hit with a meteorite in this century.
    Maybe two.
    Some people will do anything for their 15 minutes of fame...


Sterling K. Webb
----------------------------------------------------
----- Original Message -----
From: "Darren Garrison" <cynapse_at_charter.net>
To: "Ron Baalke" <baalke_at_zagami.jpl.nasa.gov>
Cc: "Meteorite Mailing List" <meteorite-list_at_meteoritecentral.com>
Sent: Monday, July 31, 2006 12:57 AM
Subject: Re: [meteorite-list] British Study Attempts to Calculate Odds
ofBeing Hit By a Meteorite


On Sun, 30 Jul 2006 19:13:44 -0700 (PDT), you wrote:

>This pointed out that eight meteorites of up to 25lb penetrated the
>atmosphere each year and if they landed would have a lethal area of the
>size of an average city back garden.

Huh? A 25 pound meteorite falling would kill everone in an "area of the
size of
an average city back garden"?

>
>But every 80 years or so a meteorite weighing up to a ton breaks through
>with a killing zone of 133 acres.

A one ton meteorite killing everone within 133 acres?

Something must be lost in the translation from journal to newspaper there.
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Received on Mon 31 Jul 2006 04:59:04 AM PDT