[meteorite-list] Scientists Use Lasers to Simulate Shock Effects of Meteorite Impact on Silica

[Ron Baalke]

https://www6.slac.stanford.edu/news/2015-09-14-scientists-use-lasers-simulate-shock-effects-meteorite-impact-silica.aspx

Scientists Use Lasers to Simulate Shock Effects of Meteorite Impact on Silica

SLAC Study Reveals its Unexpectedly Fast Transformation into a Compressed Form

Stanford University
September 14, 2015

Scientists used high-power laser beams at the Department of Energy’s SLAC 
National Accelerator Laboratory to simulate the shock effects of a meteorite 
impact in silica, one of the most abundant materials in the Earth's crust. 
They observed, for the first time, its shockingly fast transformation 
into the mineral stishovite - a rare, extremely hard and dense form of 
silica.

You can scoop up bits of stishovite at the scene of meteorite impacts, 
such as a 50,000-year-old meteor crater in Arizona that measures about 
3/4-mile across and about 570 feet deep. A similar form also exists naturally 
at the extreme pressures of the Earth's mantle, hundreds of miles below 
ground.

The Speed of Stishovite

In the experiment at SLAC, researchers used lasers to create a shock wave 
in samples of silica glass. The heat and compression of this shock wave 
caused tiny crystals, or "grains," of stishovite to grow within just a 
few nanoseconds, or billionths of a second. This speed defies predictions 
that the changes take tens or even hundreds of times longer.

"The beauty here is that the quality of the data enabled us to make a 
measurement that gives us entirely new insight into the mechanism for 
this transformation," said Arianna Gleason, who led the experiment at 
SLAC's Linac Coherent Light Source (LCLS) X-ray laser, a DOE Office of 
Science User Facility. The work was published in the Sept. 4 issue of 
Nature Communications.

"Figuring out how atoms rearrange themselves in this material is important, 
and to our great surprise, what we expected to be a slower process is 
really rapid," said Gleason, who was a postdoctoral researcher at SLAC 
and Stanford University at the time of the 2012 experiment and is now 
a postdoctoral fellow at Los Alamos National Laboratory. 'That was not 
known before. LCLS gave us access to this ultrashort timescale combined 
with the capability to generate a shockwave, which is unique."

New Insight in Planetary, Materials Science

The improved understanding gives researchers new insight about the basic 
properties of silica and other materials, and could ultimately lead to 
improved models of planetary formation and composition and new approaches 
for designing future materials with improved functionality, such as strength.

In the LCLS experiment, researchers aimed two optical laser pulses at 
the same point on the silica samples. They used brilliant, ultrashort 
X-ray pulses produced by LCLS to explore the resulting shock effects on 
a timescale of femtoseconds and from an atom's-eye view. They varied the 
arrival time of the X-ray pulses to pinpoint the speed of the material's 
transformation.

Researchers have since conducted follow-up experiments that explore other 
shock properties in this and other materials, including metals and semiconductors 
heavily used in industry.

"We're really just scratching the surface of being able to visualize transformations 
during shock compression in real time via snapshots with LCLS, and in 
understanding the states of materials in the interior of  our own planet 
and other planets,' said Gleason.

Other scientists participating in the study were from Los Alamos National 
Laboratory, LCLS, the Stanford Institute for Materials and Energy Sciences 
(SIMES) at SLAC, Stanford, Washington State University, Lawrence Livermore 
National Laboratory, the Carnegie Institution of Washington and the Center 
for High Pressure Science and Technology Advanced Research in Shanghai. 
The work was supported by the DOE Office of Science, National Science 
Foundation, Mineralogical Society of America and the Laboratory Directed 
Research and Development program at Los Alamos Laboratory.

Citation: A.E. Gleason, et al., Nature Communications, 4 September 2015 
(10.1038/ncomms9191)

For questions or comments, contact the SLAC Office of Communications at 
communications at slac.stanford.edu.

SLAC is a multi-program laboratory exploring frontier questions in photon 
science, astrophysics, particle physics and accelerator research. Located 
in Menlo Park, Calif., SLAC is operated by Stanford University for the 
U.S. Department of Energy's Office of Science.

SLAC National Accelerator Laboratory is supported by the Office of Science 
of the U.S. Department of Energy. The Office of Science is the single 
largest supporter of basic research in the physical sciences in the United 
States, and is working to address some of the most pressing challenges 
of our time. For more information, please visit science.energy.gov.