[meteorite-list] Extraterrestrial Impact Recreated in the Laboratory

From: Charles Viau <cviau_at_meteoritecentral.com>
Date: Wed Jun 30 13:04:03 2004
Message-ID: <20040630041038.2DC8A26604_at_ns4.beld.net>

Agree with Craig.. The simpler tests using a drop of milk in a puddle
produced much better information. You could see the concentric rings being
created (complex ring structure crater) as the central mass sank, upwelled,
and sank again. By using the fluid dynamics math on the liquid, and
extrapolating to the fluid effects that sand and rock would have, you could
understand how the concentric rings were frozen in time, when the energy
level dropped low enough so that the material stopped behaving like a fluid,
thus producing the multiple rings in the crater, and a domed central uplift
in the exact center.. I do not see this behavior modeled well enough in this
new test, to call in unique.

 

CharlyV

 

  _____

From: meteorite-list-bounces_at_meteoritecentral.com
[mailto:meteorite-list-bounces_at_meteoritecentral.com] On Behalf Of
MexicoDoug_at_aol.com
Sent: Tuesday, June 29, 2004 6:38 PM
To: meteorite-list_at_meteoritecentral.com
Cc: lohse_at_tnw.utwente.nl
Subject: [meteorite-list] Extraterrestrial Impact Recreated in the
Laboratory

 

>>??????

>>I've seen video of this type of test being performeded numerous times on
>>various TV programs on places like The Discovery Channel, etc.

>>So unless I missed something here, what was so special about this test?
>>Craig

Hola Craig, I think the "special" aspects you could be missing is that, the
"test" is far more rigorous than a video on The Discovery Channel! It seems
that the Dutch group is quite experienced with integrating mathematical
"singularity" events into coherent explanations, which bridge observations
to theory. Like asking "how does a bubble really pop and can we predict the
volume or pitches of the sound wave produced?". While most of us are happy
modeling that with some chewing gum or bubble bath, it sounds like these
curious physicists probably can get into the almost philosophical question
of how the weakness develops, at what limit it opens up, and where, and how
that affects the trajectories of the material that goes flying.

Keeping in mind that the holy grail of this sort of work ought to be
scalability:

In the impactor case of this study, they chose to model the surface of the
experiment impact site based on aerated (carefully fluffed) uniform sized
particles ("sand").
  The reason for this, it seems, was to create a "solid" to be impacted
which maximized the relative amount of energy the incoming iron impactor
had. In other words, rather than create a super accelerated Hulk smashing
projectile hitting compacted (higher stored potential energy) earth, in
which events are apparently experimentally much more difficult and less
reliable to set up on reasonable timescales and energies, it was easier to
create a situation where the impact site had a lot less energy. They
determined that the granulated impacted materials act somewhat like water
and could be mathematically explained by common engineering fluid flow
(Euler) equations, which reduced into a special case called a Rayleigh-type
equation.

This was an intriguing result, in the authors' opinions, as it is
theoretically scalable. And scalability is what all of these videos wish
they could do. But the fact remains - no one has ever been able to record a
major impact event, so a new scalable model has the potential to give us
much insight. The authors claimed, further, that a liquid (predictable)
model is general not accepted, and these impact events are too easily
written off as not reproducible - to random -

So being a nice combination of experimental-theoretical physicists, they
more rigorously developed the major ideas on the blackboard. It looks like
their major result was that the iron tunnels into the site, and after
mathematically modeling the tunnel created which collapses, and then solving
for that point of first contact in the collapse, they derived equations from
this simple experimental design which agreed with the observations of the
creation of a "splash" and more importantly two "jets": one forward into the
tunnel, and the other exactly reverse, which implications were not covered
well in the post (see next paragraph).

They then further derived what sort of patterns should be created ... and
scaled them up as permitted by their clever model. Their major result here
was that the peripheral splash didn't cause most of the material thrown out
as (tektites if you believe, or ejecta from earth to become earth
meteorites). That honor was shown to be from the reverse jet created upon
the not turbulent closing of the tunnel. There was a further observation
not mentioned in the initial abstract posted here, that I think is very
significant. That is that for a liquid like water, no matter what the entry
angle, the resulting jet goes vertical. But in this case, unlike water, it
went exactly backward along the entry trajectory.

Furthermore, they were able to characterize what layers (call them
sediments) ended up where. So the suggestion is that using this type of
model to look for different impactites as these predictions go could be a
good tool to understand what happened in the big time events.

I am sure I got some of it backwards, so I am copying this post to Dr.
Detlef Lohse, the first author of the work, who I hope can offer further
comment on the work for the meteorite collecting community. I think it is
an excellent approach, though my main question would be on the reasonability
of the assumption of using aerated sand. Could the compressibility of the
chosen substrate could create fluid-like behavior in something initially
that was much less compressible, based on the modeling?


Saludos
Doug Dawn
N. 25.4? W. 100.2?
Mexico


In a message dated 6/29/2004 12:50:03 PM Eastern Daylight Time, Ron Baalke
<baalke at <http://six.pairlist.net/mailman/listinfo/meteorite-list>
zagami.jpl.nasa.gov> writes:

>
>
>http://physicsweb.org/article/news/8/6/12
>
>Extraterrestrial impact created in the lab
>Belle Dume
>Physics Web
>22 June 2004
>
>Scientists in the Netherlands have successfully recreated a
>small-scale meteoritic impact in the laboratory for the first
>time. The novel yet simple experiment, devised by Detlef Lohse
>and colleagues at the University of Twente, involves dropping a
>small steel ball onto the surface of a sand bed. The results
>could shed more light on the processes occurring during
>large-scale impacts on Earth and other planets in the solar
>system.
>
>Lohse and colleagues first prepared a sand bed, around 25 cm
>thick, from fine sand grains measuring on average 50 microns
>across. The sand was "decompactified" by blowing air through it
>and then allowed to settle in an extremely loose-packed structure,
>so that it essentially behaved like a fluid. Next, the scientists
>dropped a steel ball, with a diameter of 2.5 cm, onto the sand
>from various heights and angles while taking images with a
>high-speed digital camera.
>
>The Twente team observed a series of well-defined steps: on impact,
>sand is blown away in all directions to form a crown-shaped splash.
>The ball then penetrates the sand and creates a void, which then
>collapses under the influence of the hydrostatic-like pressure of
>the sand. This pressure subsequently ejects sand grains into the
>air to form jets (see figure). Using numerical simulations the
>scientists developed a theory to explain how the void collapsed.
>
>"We have shown that the impact of an object on loosely packed
>granular material can be well described by a simple, fluid
>dynamical continuum model. So in our system sand behaves like
>water!" team member Devaraj van der Meer told PhysicsWeb. "This
>is very surprising since it has often been argued that, in general,
>no continuum description of granular materials is possible," he
>added.
>
>"There is a striking similarity with the large-scale impact of
>meteors and other celestial objects on the surface of the Earth --
>for example the Chixulub impact crater in Yucatan, Mexico, thought
>to be responsible for the extinction of the dinosaurs -- and our
>experiment," said van der Meer. "Our scaled-down granular
>experiments under laboratory conditions possibly capture the
>essential features of these crucial events in the history of our
>planet."
>

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