The mysterious glass “yellowgreen jewels that have smooth surfaces sculpted by the incessant wind.”
Red Storm simulated the airburst and impact of a 120-meter diameter stony asteroid, shown in this sequence. Meteoric vapor mixes with the atmosphere to form an opaque fireball with a temperature of thousands of degrees. The hot vapor cloud expands to a diameter of 10 km within seconds, still in contact with the surface.
It was in 1932 that British explorers in Model-A Fords first visited this area of western Egypt, where they discovered a mysterious yellow-green glass scattered across the surface. Ever since, Libyan Desert Glass has fascinated scientists, who have dreamed up all sorts of ideas about how it could have formed. It’s too silicarich to be volcanic. In some ways it resembles the tektites generated by the high pressures associated with asteroid impacts. That observation is the starting point of a scientific debate that became the subject of the documentary filmed for National Geographic and BBC.
I was chosen to participate in the role of a dissenter from the preferred explanation that the glass was formed by direct shock-melting by a crater-forming asteroid impact. I had stumbled into the debate by accident in 1996, when I attended a conference on the subject of the 1908 explosion of an asteroid or comet that knocked down nearly a thousand square miles of trees in Siberia. I stayed an extra day to attend a meeting about the desert glass, where I argued that similar — but larger — atmospheric explosions could create fireballs that would be large and hot enough to fuse surface materials to glass, much like the first atomic explosion generated green glass at the Trinity site in 1945.
King Tut connection
Shortly after that workshop, one of the Italian organizers made a discovery that raised public interest in the subject. Vincenzo de Michele visited the Egyptian Museum in Cairo, and noticed that one of King Tutankhamun’s jeweled breastplates contained a carved scarab that looked suspiciously like a piece of the glass. A simple optical measurement confirmed the match in 1998. The connection of a catastrophic explosion with the treasures of ancient Egypt became a sure-fire formula for a documentary.
Last December, when I was first asked by the producer to be interviewed, I was a little skeptical. After all, television is known more for sensationalism than for scientific accuracy, and the King Tut connection had fueled pseudoscientific speculation on the web. One website even presents fanciful “Evidence for Ancient Atomic War,” making the case that Egyptians had detonated nuclear weapons (but ignoring the fact that the glass is 29 million years old). Did I want to be part of this?
Fortunately, I was assured by other scientists that this would be a legitimate documentary that would focus on natural explanations for this enigmatic glass. In February, I found myself in Cairo with Dr. de Michele, getting a firsthand look at King Tut’s glass scarab and preparing for nine days in the desert.
Great Sand Sea
Our jumping-off point was the Bahariya Oasis, a large valley of villages and adobe houses. After the 300-kilometer drive on a two-lane highway through the lifeless desert, the irrigated fields were startlingly green — the last green we would see for some time.
Leaving the road, we embark on a 1,000-km voyage across the Great Sand Sea. Despite the lack of water, that name is apt. Like mariners, we don’t follow a specified route. We are guided by the sun, compasses, dead-reckoning, and (like modern sailors) GPS. If the dunes are the swells of the open ocean, our first day’s trip is an excursion though a field of icebergs. Towering monuments, hoodoos, and mesas of stark white limestone provide a maze through which we meander, opening up to a featureless flat sand plain.
Our Egyptian outfitter, his French partner, and the local drivers and crew make this trip several times every year. They plot their GPS tracks on satellite images downloaded from the web. They never repeat the same route, but offset their trips by enough distance that they explore parts of the desert that have never been crossed before.
February in the Sahara is cool, and the wind blows so hard on the Great Sand Sea that it can be hazy like a marine fog. Our meals here are accompanied with sugar saturated tea brewed Bedouin-style over an open flame of apricot wood carried from the orchards of Bahariya.
To the southwest, the rolling sand builds to great dunes and the sea rises. Vehicles frequently get stuck and have to be rescued by digging and driving them up special aluminum ramps. It takes a special sailor’s eye to distinguish between a safe hard surface and the treacherous soft sand, especially at 100 kilometers/hour. Arabic, French, and English conversations crackle over the radio, and throbbing Egyptian music plays on the driver’s iPod.
He approached the assignment with some healthy skepticism, but now believes the effort bore some scientific fruit. Just before we reach the site of the glass, the dunes become linear — unbroken parallel ranges running north-south for hundreds of kilometers. Here we must carefully pick our crossings, and then we run at high speed southward in the corridors between the dunes, the “freeways” that have been used by nomads for centuries (as evidenced by 100-year-old camel skeletons).
On our third day after leaving the last road, our maps tell us we are within the area where glass has been found. We stop to look. There are pieces of sandstone everywhere, and no plants in sight. It looks strikingly like the surface of Mars, and sand sifts underfoot. The first bits of glass we find are yellow-green jewels that have smooth surfaces sculpted by the incessant wind. We hold them up to the sun to see how the light refracts and scatters. This is probably what the Pharaohs did with their piece, and the Neolithic people before them.
Nine days of geologic exploration and discussion bore fruit. You get to know your colleagues well during long days driving and long nights in camp. Everyone figures out the strengths and weaknesses in one another’s ideas. It would be premature to claim that we solved the mystery, but new friendships and collaborations have emerged, and renewed interest in this scientific mystery has energized debate over this unique glass.
Applying high-performance computing to a scientific mystery
While most natural glasses are volcanic in origin, rare exceptions are tektites, formed by shock melting associated with hypervelocity impacts of comets or asteroids. The Libyan Desert Glass falls into neither of these categories and has baffled scientists since its 1932 discovery.
Sandia physicist Mark Boslough’s study of the 1994 collision of Comet Shoemaker-Levy 9 with Jupiter provided an opportunity to model a hypervelocity atmospheric impact. Along with observation of the actual event, the model provided insights that provided a likely scenario for the formation of the Libyan Desert Glass.
Using Sandia’s Red Storm supercomputer, Boslough and his team ran a three-dimensional simulation, using huge amounts of memory and processing power. The simulation supports the hypothesis that the glass was formed by radiative heating and ablation of sandstone and alluvium near the “ground zero” of a 100- megaton or larger explosion caused by the breakup of a comet or asteroid.
Expedition camp was set up in “corridor B” in the southern part of the Great Sand Sea, within the area of Libyan Desert Glass. The corridors — made up of relatively recent gravels and separated by linear dunes — have long provided travel routes in this remote area.
The shock-physics simulations show a 120-meter-diameter asteroid entering the atmosphere at a speed of 20 kilometers/second and breaking apart just before hitting the ground. The fireball generated by the explosion remains in contact with the Earth’s surface at temperatures exceeding the melting temperature of quartz for more than 20 seconds. The fireball and the air speed behind the blast wave (hundreds of meters per second during the 20 seconds) are consistent with melting and rapid quenching to form the Libyan Desert Glass.
Although the risk to humans for such an impact is remote, it is not negligible, Boslough notes. The precise probability of such an event and its consequences are difficult to calculate, but research on large aerial bursts is forcing risk assessment to recognize and account for these large natural processes. Expedition camp was set up in “corridor B” in the southern part of the Great Sand Sea, within the area of Libyan Desert Glass. The corridors — made up of relatively recent gravels and separated by linear dunes — have long provided travel routes in this remote area.
By Mark Boslough