Very Nice Calculator, Keith
And useful for a wide variety of cases. A sophisticated
model behind it. But... we know E. P. -- I suspect he's
interested in Big Thumpers, mostly. And the bigger
(and faster) the impactor, the more energy-dominated
the event becomes. And since the topic was the K-T
Visitor, I assumed we were talkin' Big... Not "the size
of Texas," as the memorable Billy Bob Thornton line
has it, but Big...
I noted that I stole this from the very best sources,
namely John S. Lewis' "Physics and Chemistry of
the Solar System, Second Edition" (pp.438-445).
And simplified it slightly.
And when I plug suitably big and fast impactors
into your model, I get results essentially similar
to the thumb rules, but that's because I'm choosing
events in size Large, X-Large, and 2X-Large...
No, it's the Devilishly Small impactors, where a
variety of factors matter greatly, that are a mess
to calculate. Now, I will go back to my favorite
Impact Calculator Game: finding the inputs that
will land a 100-ton HOBA without making a crater...
or a pit.
Sterling K. Webb
----------------------------------------------------------------------
----- Original Message -----
From: "Keith Holsapple" <[email protected]>
To: "Sterling K. Webb" <[email protected]>
Cc: "E.P. Grondine" <[email protected]>;
<[email protected]>; "ACC Bill Allen"
<[email protected]>; "Astronomer" <[email protected]>; "Ted
Bunch" <[email protected]>; <[email protected]>; "phil burns"
<[email protected]>; <[email protected]>;
<[email protected]>; <[email protected]>; <[email protected]>;
"Duncan" <[email protected]>; "Leroy Ellenberger"
<[email protected]>; "Richard Firestone" <[email protected]>;
"Richard Firestone" <[email protected]>; "George Howard"
<[email protected]>; "Elton Jones" <[email protected]>;
"Kennett" <[email protected]>; "Bob Kobres" <[email protected]>; "Raoul
Lannoy" <[email protected]>; "W. Bruce Masse" <[email protected]>;
<[email protected]>; "bernd pauli" <[email protected]>;
"Benny Peiser" <[email protected]>; "Tree Rings"
<[email protected]>; "Peter Schultz" <[email protected]>;
<[email protected]>; "Oscar Alfredo Turone" <[email protected]>;
"Allen West" <[email protected]>
Sent: Wednesday, April 27, 2011 1:58 PM
Subject: Re: [meteorite-list] KT extinction impacts
I think we can make much better estimates based on modern crater scaling
theories than the old (1960's) energy-based ones. And while the scaling
may be complex to a newbie, it is easily evaluated: I invite anyone to
make use of my web page at
http://keith.aa.washington.edu/craterdata/scaling/index.htm and push the
buttons to estimate the crater from any impact or explosive source.
On Apr 26, 2011, at 9:55 PM, Sterling K. Webb wrote:
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 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 at the level of the target surface, then the
crater excavation process is strength limited (the "g"
equals the surface gravity of the planet; in the case
of Earth, g = 1).
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,
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"
<[email protected]>
To: <[email protected]>; "ACC Bill Allen"
<[email protected]>; "Astronomer" <[email protected]>; "Ted
Bunch" <[email protected]>; <[email protected]>; "phil burns"
<[email protected]>; <[email protected]>;
<[email protected]>; <[email protected]>; <[email protected]>;
"Duncan" <[email protected]>; "Leroy Ellenberger"
<[email protected]>; "Richard Firestone" <[email protected]>;
"Richard Firestone" <[email protected]>; "keith holsapple"
<[email protected]>; "George Howard"
<[email protected]>; "Elton Jones" <[email protected]>;
"Kennett" <[email protected]>; "Bob Kobres" <[email protected]>;
"Raoul Lannoy" <[email protected]>; "W. Bruce Masse"
<[email protected]>; <[email protected]>; "bernd pauli"
<[email protected]>; "Benny Peiser" <[email protected]>;
"Tree Rings" <[email protected]>; "Peter Schultz"
<[email protected]>; <[email protected]>; "Oscar Alfredo Turone"
<[email protected]>; "Sterling K. Webb"
<[email protected]>; "Allen West" <[email protected]>
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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