[meteorite-list] Asteroid impact effects

From: Matson, Robert <ROBERT.D.MATSON_at_meteoritecentral.com>
Date: Thu Apr 22 10:31:29 2004
Message-ID: <AF564D2B9D91D411B9FE00508BF1C86904EE5A09_at_US-Torrance.mail.saic.com>

In response to (I believe) Sterling, Stan wrote:

> I think you make impact modeling sound alot more guesswork than it
> actually is, or may be.

> What we know of the effects caused by large explosions are based
> upon, without any exageration, the results of literally thousands
> of sets of experimental data. we can predict how such impacts will
> scale pretty darn regularly. Sure there are variables at play such
> as the type of impact site (bedrock vs water for example) angle of
> incidence, ect, but for an event such as this, surely those in the
> know would take account for such variables in their attempts to
> predict the outcome.

Ahh, but here's where you're mistaken. Many of the most important
variables determining the long-term effects of an impact are unknown
and unknowable. Sure, you can compute the basic energy of an impact
based on mass and velocity, but nobody can offer more than a guess
as to the long-term *interaction* of that energy with the global
ecosystem. One of the most important variables is the quantity
and atmospheric lifetime of tropospheric dust. You have a function
with many variables:

D_trop(t) = f(Vb,Mb,Cb,Ce,theta,...?)

where D_trop(t) = amount of tropospheric dust as a function of time
      Vb = velocity of impacting body
      Mb = mass of impacting body (asteroid/comet)
      Cb = composition of impacting body
      Ce = composition of earth impact location
      theta = angle of impact

You have to know not only the initial quantity of material ejected
into the troposphere, but the distribution of particle sizes produced,
their reflectivities, their endurance, and their interaction with upper
atmospheric global circulation patterns. Further complicating the
picture are the effects of fires (soot) and gasses (H2O, CO2, CO, NO2,
SO2, etc.) introduced into the atmosphere. The shutdown in
photosynthesis will also change the O2-CO2 balance, altering the
greenhouse effect.

Global weather is a chaotic system, and thus even if you have
perfectly quantified all the imaginable variables, the long term
behavior of the overall system is nevertheless unpredictable.
Even the tiniest change in one variable can completely alter the
outcome.

Given that our current state-of-the-art atmospheric models are still
incapable of reproducing past global temperatures with any accuracy,
I don't see how there's any hope of being able to quantify the earth's
long term (months or longer) response to a large impact. --Rob
Received on Sat 28 Feb 2004 08:30:46 PM PST