[meteorite-list] Serious question?

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Thu Apr 22 10:29:57 2004
Message-ID: <3F6A503B.79EC28E7_at_bhil.com>

Hi, Steve, and all,

    When you are talking about a large impactor, the physical properties of the
impactor material become entirely irrelevant. By the time you get up to a
one-kilometer diameter impactor, or a ten-kilometer diameter impactor, it
wouldn't matter whether the impactor was made of iron or stone or ice or
styrofoam or oak tees or whale carcases or bales of old Iraqi dinars!
    When the impactor impacts, the entire kinetic energy of the body is
degraded to free heat with remarkable efficiency. When you reach the point
where the kinetic energy per gram of impactor is greater than the energy
required to boil one gram of the impactor substance, you get vapor and nothing
but vapor.
    With an iron impactor (harder to boil than old Iraqi money), that point is
pretty much reached with objects only a fraction of the size of a
0.10-kilometer impactor like Canyon Diabolo (except for that little layer on
its backside). And since even the slowest approaching body will end up striking
a planet's surface at a velocity at or exceeding the planet's escape velocity,
there are no "slow" impactors.
    The only materials in the universe tough enough to survive a planetary
impact without going Pooof! on impact are neutronium (the condensed matter of
which neutron stars are made) and other physics oddities, like black-hole-ium
(or small black holes, in other words).
    It has been suggested that the entire Northern hemisphere of Mars (which is
much smoother and lower than the Southern hemisphere) is an immense and ancient
impact basin covering half the planet! Now, that would have been one heck of an
impactor!


Sterling K. Webb
-----------------------------------------------------------------------
"S. Singletary" wrote:

> At 08:55 PM 9/18/2003 +1000, chris sharp wrote:
> >The iron impactor disintegrated and spread iron all over the planet in
> >a fallout cloud and created a layer of iron rich material on the
> >surface.
>
> My knee-jerk reaction to that is to think about the large iron meteorites
> in our collections. They tend to be the most competent and coherent and
> hence will hold together on impact. It doesn't seem likely to me that an
> iron will disintegrate in the fashion you are talking about on impact. I'm
> not sure of that, just my first reaction to the statement.
>
> Steven
>
> Steven Singletary
> 54-1224
> Dept. Earth, Atmospheric and Planetary Sciences
> M.I.T.
> Cambridge, MA, 02139
> Tel-617.253.6398
> Fax-617.253.7102
>
> Blue Skies!
Received on Thu 18 Sep 2003 08:39:24 PM PDT


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