X-Message-Number: 19296
Date: Mon, 17 Jun 2002 00:58:10 -0700 (PDT)
From: Jeff Davis <>
Subject: Re: Why the moon has round craters

Friends,

In Message #19284,  Subject: Why the moon has round
craters.  Date: Sat, 15 Jun 2002 11:08:46 -0700,
"George Smith", <>, wrote:

> Apparently no one knows.

            <snip>

George, you know I'm on your side 99% of the time, but
this is a bit silly.  Have you really asked the right
people? 

You'll find a list here, 

http://www.lpi.usra.edu/meetings/LPSC98/pdf/sess04.pdf

of people likely to possess the appropriate expertise,
which I came up with by doing a google search for
"Theory of impact crater formation"  

Pop off a little email to various of these folks;
something like, "Why is it that all impact craters
seem to be round, and none seem to be elongated?
It seems reasonable that craters from oblique impacts
might be elongated, but I've never seen any that were
shaped that way.  Is there an explanation for this? 
If this isn't your particular area of expertise, but
you know the guy/gal to ask, please tell me who that
person is.  Thanks.

    -------------------------  
> ...I decided I would ask a friend...

Not an entirely unreasonable approach,

> (a physicist who asked to not be named) 

And after seeing his answer, I can understand why.

> ...and forwarded him the email.

> Here is part of what he wrote back to me:

<snip seemingly reasonable stuff until>

> "Furthermore, the last I checked, the BOILING point
of rock is pretty high.  The immense pressure of the
entire Earth on its core fails to do anything more
than melt it.  

At which point I gasped, and began to hope, for his
sake, that he's not giving up his day job as a UPS
driver.  Or perhaps--god help us--he works at a
nuclear power plant?  His name isn't, by any chance,
Homer Simpson?  Oh, wait a minute, right, Homer's just
a cartoon character. Whew, that was scary for a
moment.

The pressure at the earth's core is not the cause of,
and has no bearing on, the temperature of the core 
(which happens to be solid--not because of the temp,
but rather because of the high pressure, and which
happens to be iron, not rock).  The temp of the core
is the result of (1) the initial accumulation of
energy during the planet's formation--the accreting
material, accelerated as it fell inward, converted its
gravitational potential energy to kenetic energy,
which, upon impact, was converted to heat,... 4 1/2
billion years ago, and (2) the gradual release of
energy from radioactive decay in those intervening 4
1/2 billion years.       

 <snip>

> "In short, this fellow doesn't know what he's
talking
about and probably doesn't realize it."

Perfectly describes your 'physicist' (wink, wink)
friend.  To be a bit more generous, the answer to this
question may not lie where one would initally expect
to find it, so that first guesses, given in good faith
by intelligent and educated persons such as your
friend, miss the mark. 'Trick questions' wrongly
guessed at don't really reflect badly on the guessers.

<snip>

> Why does the Moon have round craters?

> Apparently no one really knows.

Are you sure, George?  I still think you haven't
looked well enough?

By the way, if I were to hazard a guess of my own,
after reading only a few paragraphs as I performed
that google search earlier, I would say that at the
pressures, temperatures, and energies involved in such
impacts, the subject materials behave as fluids,
wherein will be found the explanation, which is not
intuitively expected by the average ponderer.  

As always, George, I remain an admirer of all those
brave souls who, like yourself, dash enthusiastically 
to the extreme of whatever the limb, passionate to
redefine the limits of the possible.
 
Regarding the cryonics endeavor:

SUCCESS IS A NEAR CERTAINTY

Best, Jeff Davis

   "My guess is that people don't yet realize how
          "handy" an indefinite lifespan will be." 
                            J Corbally 


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