[meteorite-list] KT extinction impacts

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Wed, 27 Apr 2011 00:23:56 -0500
Message-ID: <1CF6B8A59D104C60AE710884081FAE61_at_ATARIENGINE2>

Dear E.P.

> Sterling, do you have a public formula handy for
> converting craters into megatons in a very rough
> number? ...perhaps he will generate a very easy
> to use > oversimplified rough approximation formula
> for Earth impacts.

There ARE some simplified model equations for crater
size and impact energy, hence impactor size, and
there certainly are some quick and rough ones.
[Note: I stole all this from the very best sources...]

Consider a 100-m chunk of asteroidal material
encountering the surface of a rocky planet at a speed
of 20 km/s. The kinetic energy density of the impactor
is 1/2 (2 x 10^6)^2 or 2 x 10^12 erg/g. The energy
required to crush a typical rock is a little above
10^8 erg/g. [A joule is 10^7 ergs]

To heat it to its melting point requires about 10^10
erg/g and to vaporize it requires less than 10^11
erg/g. Thus the impactor carries enough kinetic
energy to not only vaporize itself completely, but also
crush up to roughly 1000 times its own mass of target
rock, melt roughly 100 times its own mass, or vaporize
about 10 times its own mass. Alternatively, it carries
enough kinetic energy to accelerate 100 times its own
mass to a speed of 0.1 times its impact speed.

In reality, an impact does all of these things to some
degree and divides its energy over all these possible
outcomes. Thus an impactor may crush 1000 times
its own mass of rock, melt 10 times its mass,
vaporize a few times its own mass, and eject 100
times its mass at speeds of tens to hundreds of
meters per second and still give off a substantial
amount of energy as seismic waves and radiation
from the fireball.

Crater sizes are of course generally related to the
kinetic energy content of the impactor. For relatively
SMALL impacts the critical factor in determining the
target's resistance to the explosion is the strength of
the material, S (dyn/cu.cm.). If S > density x g x crater
diameter (the "g" equals the surface gravity of the
planet; in the case of Earth, g = 1)at the level of the
target surface, then the crater excavation process is
strength limited .

In this case, the diameter scales as:

           D (km) roughly equals the cube root of W,

where W is the explosion energy in units of millions of
tons of TNT equivalent (megatons; Mt). For very large
impacts, no material has enough strength to matter, and
the cratering process depends only on the gravitational
environment in which it occurs:

           D (km) roughly equals the fourth root of W/g

For a rule of thumb for craters from a few kilometers up
to 100 km or more with impactor speeds of 25-30 km/s,
the crater is nine or ten times the size of the impactor,
for 10-12 km/s impacts, the crater may only be 5-6 times
the size of the impactor

If you find a 100-km crater on Earth, you can figure
the impactor was 8-9 km if fast and 11-12 km if slow,
and delivered 100 (crater diameter) ^ 4, or 100,000,000
megatons. Chicxulub, in other words.

You can do that much with a thumb...


Sterling K. Webb
---------------------------------------------------------------------------

----- Original Message -----
From: "E.P. Grondine" <epgrondine at yahoo.com>
To: <meteorite-list at meteoritecentral.com>; "ACC Bill Allen"
<ballen at hohmanntransfer.com>; "Astronomer" <meb at star.arm.ac.uk>; "Ted
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<pib at pibburns.com>; <c.leroy.ellenberger at wharton.upenn.edu>;
<cavetank at aol.com>; <dallas at ldeo.columbia.edu>; <dja at star.arm.ac.uk>;
"Duncan" <duncansteel at grapevine.com.au>; "Leroy Ellenberger"
<c.leroy at rocketmail.com>; "Richard Firestone" <rbfirestone at lbl.gov>;
"Richard Firestone" <rbf at lbl.gov>; "keith holsapple"
<holsapple at aa.washington.edu>; "George Howard"
<george at restorationsystems.com>; "Elton Jones" <mstreman53 at yahoo.com>;
"Kennett" <dkennett at uoregon.edu>; "Bob Kobres" <bkobres at uga.edu>; "Raoul
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"Benny Peiser" <benny.peiser at thegwpf.org>; "Tree Rings"
<m.baillie at qub.ac.uk>; "Peter Schultz" <Peter_Schultz at brown.edu>;
<tankerkh at uc.edu>; "Oscar Alfredo Turone" <oaturone at sinectis.com.ar>;
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Sent: Tuesday, April 26, 2011 1:32 PM
Subject: [meteorite-list] KT extinction impacts


> Hi all -
>
> Ahem.
>
> Jay, you are right that it is a hypothesis that the KT impacts were
> from fragments of the same comet.
>
> The other explanation, and a far more likely one, now that you mention
> it, is that Clube and Napier's injection mechanism was at work, and
> multiple comets hit at roughly the same time.
>
> In this summary, note the pooling of oil in the fractures, which may
> go a long way toward explaining the lack of public publications:
>
> http://starmon.com/KT_craters.html
>
> http://bi154.dhcp.ttu.edu/extinction/chatterjee+rudra08.pdf
>
> It is also interesting that 41 major scientists signed an open letter
> declaring that Chicxulub caused the extinction of the dinosaurs
> shortly before Chatterjee's work was widely circulated.
>
> In doing this they followed me in the earlier mistake I made in
> responding to Keller's nonsense several years earlier.
>
> In answer to the nuclear effects of hypervelocity impacts, it appears
> that photons in the reaction reach an energy level capable of
> splitting neutrons (nucleons) into neutrons and protons, resulting in
> higher 10 Berylium and 14 Carbon levels. Even in impacts much smaller
> than these.
>
> (Sterling, do you have a public formula handy for converting craters
> into megatons in a very rough number? Anything better than the Purdue
> online impact simulator? I have misplaced my Excel spreadsheet.
> Stroke.
>
> Can you also speak to the issue of the energy in the 10Be/14C
> production?
> Is it a fission addition, or a fission subtraction?)
>
> By the way, there is a special on my book "Man and Impact in the
> Americas" over at the cosmictusk.com.
>
> E.P. Grondine
> Man and Impact in the Americas
>
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Received on Wed 27 Apr 2011 01:23:56 AM PDT