[meteorite-list] Extraterrestrial Impact Recreated in the Laboratory

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Jun 29 12:50:23 2004
Message-ID: <200406291650.JAA19655_at_zagami.jpl.nasa.gov>

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."
Received on Tue 29 Jun 2004 12:50:03 PM PDT