Global supercomputer leader Cray Inc. today announced that researchers running simulations on the Cray supercomputer at Sandia National Laboratories have re-created what could have happened 29 million years ago when an asteroid explosion turned Saharan sand into glass. The greenish natural glass, which can still be found scattered across remote stretches of the desert, was used by an artisan in ancient Egypt to carve a scarab that decorates one of the bejeweled breastplates buried in King Tutankhamen's tomb.
"Supercomputers now allow us to approach these problems as if we were conducting actual experiments," said Mark Boslough, the physicist at Sandia whose theory about the origins of Libyan Desert Glass sparked the research. "With this class of computer, we can run multiple simulations at such high resolution and fidelity that we can see phenomena that we wouldn't be able to predict from first principles. That means we can explore alternate possibilities as we go. It's more like doing iterative experimental science than theoretical science."
The Cray supercomputer at Sandia, nicknamed Red Storm, was developed jointly by Cray and Sandia, a part of the Department of Energy's National Nuclear Security Administration. Sandia upgraded Red Storm late last year to three times its original performance level, boosting its performance to more than 100 teraflops, or 100 trillion floating point operations per second. Red Storm is one of only three supercomputers in the world to exceed the 100 teraflops mark, according to the TOP500 results released last month.
"The Libyan Desert Glass study at Sandia is truly exciting research that crosses a number of scientific disciplines -- ranging from impact physics and geology to Egyptology," said Jan Silverman, senior vice president, corporate strategy and business development at Cray. "We are delighted to hear about how our highly scalable Cray XT(TM) supercomputer architecture allows iterative modeling techniques to find the most probable explanation. Using the computational power of our supercomputers we also see similar iterative techniques being used to optimize designs from automobiles to airplanes."
Clues To a Mystery
Until recently Earth scientists believed that natural glass can form by only two high-temperature processes. Volcanic glass, such as obsidian, can be produced when lava cools rapidly. Or, in rare cases, a glass known as tektite can form from the high pressures generated when an asteroid or comet directly impacts the earth. But compositional studies indicate that Libyan Desert Glass does not fit either of these two categories. Adding to the puzzle, scientists generally agree the Libyan glass was somehow formed by a collision with an object from space, but no one has ever been able to confirm an impact crater in the region.
Boslough found one clue to the glass mystery in the 1994 collision between the Comet Shoemaker-Levy 9 and Jupiter. That comet broke up into several pieces before it made contact with Jupiter's atmosphere, where the collisions caused fireballs that shot hundreds of miles above the planet. Boslough conjectured that if such an air burst were to occur above Earth, it might generate enough heat to fuse surface materials into glass.
Another clue was the Tunguska explosion that flattened a thousand square miles of forest across Siberia in 1908. Because there is no crater of sufficient size to have caused this event, it is generally believed that the Tunguska blast was the result of a meteoroid or comet fragment that exploded at an altitude of five to 10 kilometers (three to six miles) above the Earth's surface.
Boslough argues that a similar atmospheric explosion could have created fireballs large enough and hot enough to produce the Libyan Desert Glass. Such glass would have been forged in seconds, much like the glass that formed from super-heated sand at the Trinity site in New Mexico during the first atom bomb test in 1945. If the asteroid blast occurred above the Earth, there would be no evidence of a collision in the composition of the glass and no significant crater in the ground.
Re-creating the Blast
"What I focused on in the simulations was the explosion of the asteroid," said Boslough. "As the object entered the atmosphere it had tremendous kinetic energy. Much of that energy was converted to heat, creating a blast as hot as the surface of the sun over a large area. The fireball remained in contact with the Earth's surface for more than 20 seconds. At the same time, winds behind the blast reached a speed of several hundred meters per second. The glass formed from the rapid melting and quenching of the sandstone and alluvium on the ground."
Boslough and his colleagues at Sandia performed high-resolution hydrocode simulations on Red Storm using the CTH shock-physics code. They postulated a 120-meter diameter stony asteroid hitting the atmosphere at 20 kilometers per second and breaking up, touching off a blast equivalent to a 110 megaton bomb and producing intense heat and high-velocity winds.
According to the simulations, this explosion would have been more than sufficient to melt rocky material on the surface and then cool it quickly, the conditions necessary to form natural glass. The high winds would have accelerated the melting process by blowing away the boundary or "melt" layer that would otherwise insulate the stone from the heat.
Boslough and his group conducted a number of simulations to come up with their results.
"Multiple iterations are really important for gaining new insights," he said. "You can't plan out your whole experimental matrix and lock yourself in. When we vary the parameters, we can see new things. For example, we observed a large ring vortex during the explosion that acts as a 'lubricant' for the downward flow of mass and energy. No one had suggested that was possible before."
For more information about the Libyan Desert Glass study, go to http://www.sandia.gov/news/publications/technology/2006/0804/glass.html
If you blow up the picture you may think it's a bush fire over the hilltop and a nice flame to light your cigar with, but it's actually a bit different. You are looking at an image from the sun through a solar telescope and the flames on the edge are called prominences. Prominences are enormous clouds of hydrogen (which make up the bulk of the sun basically) held together by solar magnetic fields.
