[meteorite-list] Study shows how impact craters may form

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sat, 17 Dec 2011 15:13:41 -0600
Message-ID: <DC2E2E42B45A40EF8DD08D9E7220C079_at_ATARIENGINE2>

Thanks, Paul.

As is usual in science reporting, the "punch-line"
is never explicit. If loosely compacted impactors
make bowls and tightly compacted impactors make
central peaks, what are these types most likely to
correspond to in the real universe?

Asteroids in general are less compacted than
terrestrial materials because they form in weaker
gravitational fields, but no doubt heading the list
of tightly compacted materials are the irons.

At Meteor Crater, Arizona, the iron impactor
had already fragmented before it hit (or so they
think). I would go even further out on that limb
by guessing that bodies with an atmosphere
(like Mars) might well have fewer central peak
craters then airless bodies (like the Moon).

I say "guess" because I'm not going to sit down
and count them! Well, there's Google... 1966 study:
http://articles.adsabs.harvard.edu//full/1977LPI.....8..181C/0000181.000.html
says there's more central peaks on Mercury than
the Moon which has, in turn, more central peaks
than Mars. I would expect more iron impactors
in the refractory zone around Mercury than out
here around the Earth and Moon, and apparently
Mars' atmosphere does protect it.

All this seems to confirm the result.

Going down the list are the more solid rocks
followed by weaker rocks (like carbonaceous
stones). Some asteroids are "rubblepiles" and
have lots of internal voids. Eros and Itokawa
are made of the same rock but Itokawa is far
less dense, indicating that porosity and voids
are present

The weakest impactors would be likely be
the comets (or any icy body whether you call
it a comet or not).


Sterling K. Webb
---------------------------------------------------------------
----- Original Message -----
From: "Paul H." <oxytropidoceras at cox.net>
To: <meteorite-list at meteoritecentral.com>
Sent: Saturday, December 17, 2011 8:36 AM
Subject: [meteorite-list] Study shows how impact craters may form


> Study shows how impact craters may form
> http://dalje.com/en-world/study-shows-how-impact-craters-may-form/390016
>
> Study shows how impact craters may form. Science News.
> http://www.upi.com/Science_News/2011/10/20/Study-shows-how-impact-craters-may-form/UPI-26051319150854/#ixzz1cgD4itIS
>
> Crater shapes, UPI
> http://www.upi.com/story/image/fs/UPI-26051319150854/13191492262400/
>
> F. Pacheco- Vazquez and J. C. Ruiz- Suarez, 2011, Impact
> craters in granular media: Grains against grains. Physical
> Reviews Letters. vol. 107, no. 218001, 5 pp
> http://prl.aps.org/abstract/PRL/v107/i21/e218001
>
> Happy Holidays,
>
> Paul H.
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Received on Sat 17 Dec 2011 04:13:41 PM PST