[meteorite-list] Extraterrestrial Impact Recreated in the Laboratory

[Ron Baalke]

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."