By Neal Singer
The stunning amount of forest devastation at Tunguska a century ago in Siberia may have been caused by an asteroid only a fraction as large as those postulated in previously published estimates, Sandia supercomputer simulations suggest.
“The asteroid that caused the extensive damage was much smaller than we had thought,” says principal investigator Mark Boslough (1433) of the impact that occurred June 30, 1908. “That such a small object can do this kind of destruction suggests that smaller asteroids are something we should consider. Their smaller size indicates such collisions are not as improbable as we had previously believed.”
Because smaller asteroids approach Earth statistically more frequently than larger ones, he says, “We should make more efforts at detecting the smaller ones than we have till now.”
The new simulation — which more closely matches the widely known facts of destruction than earlier models — shows that the center of mass of an asteroid exploding above the ground is transported downward at speeds faster than sound. It takes the form of a high-temperature jet of expanding gas called a fireball.
This causes stronger blast waves and thermal radiation pulses at the surface than would be predicted by an explosion from a point-source at the height where the burst was initiated.
“Our understanding was oversimplified,” says Mark. “We no longer have to make the same relatively primitive assumptions because present-day supercomputers allow us to do things with high resolution in
3-D. Everything gets clearer as you look at things with more refined tools.”
The new interpretation also accounts for the fact that winds were amplified above ridgelines where trees tended to be blown down, and that the forest at the time of the explosion, according to foresters, was not healthy. Thus previous scientific estimates had overstated the devastation caused by the asteroid, since topographic and ecologic factors contributing to the result had not been taken into account.
Revising deflection strategies
“There’s actually less devastation than previously thought,” says Mark, “but it was caused by a far smaller asteroid. Unfortunately, it’s not a complete wash in terms of the potential hazard, because there are more smaller asteroids than larger ones.”
Mark and colleagues achieved fame more than a decade ago by accurately predicting that that the fireball caused by the intersection of the comet Shoemaker-Levy 9 with Jupiter would be observable from Earth.
Simulations show that the material of an incoming asteroid is compressed by the increasing resistance of Earth’s atmosphere. As it penetrates deeper, the increasingly dense wall of air causes it to explode as an airburst that precipitates the downward flow of heated gas.
Because of the additional energy transported toward the surface by the fireball, what scientists had thought to be an explosion between 10 and 20 megatons was more likely only three to five megatons. The physical size of the Tunguska asteroid, says Mark, would depend on its speed and whether it is porous or nonporous, icy or waterless, and other material characteristics.
“Any strategy for defense or deflection should take into consideration this revised understanding of the mechanism of explosion,” says Mark.
The work was presented at the American Geophysical Union meeting in San Francisco on Dec. 11. A paper on the phenomenon, coauthored by Dave Crawford (1541) and titled “Low–altitude airbursts and the impact threat” has been accepted for publication in the International Journal of Impact Engineering.
The research was paid for by Sandia’s Laboratory Directed Research and Development office. -- Neal Singer
Some 20,000 soldiers a year may soon be trained in interpersonal skill building and cross-cultural awareness using a videogame recently developed by researchers from Sandia and BBN Technologies.
Funded through the Defense Advanced Research Projects Agency (DARPA), the nine-month project resulted in the creation of an adaptive thinking training methodology that prepares warfighters for difficult situations in places such as Afghanistan and Iraq, says project lead and scientist Elaine Raybourn (6341).
“We are talking about training for nonkinetic engagement — interpersonal communication, negotiation skills, and interpersonal rapport,” she says. “The goal is to make soldiers better thinkers and communicators under stress.”
Elaine and her team recently delivered DARPA’s “DARWARS Ambush NK!” to the Program Executive Office for Simulation, Training, and Instrumentation (PEO-STRI), which will distribute the enhanced system to the Army and eventually the other armed forces.
The training tool is conceptually similar to an earlier multiplayer simulation game she developed several years ago. That same game is currently used by members of the US Army Special Forces to hone their skills in adaptive thinking, negotiation, conflict resolution, and leadership in cross-cultural settings. The Special Forces’ game is being used to train soldiers on a regular basis at Ft. Bragg in North Carolina. (See “Game wins award” at right.)
Like the first game, the new one developed for DARPA will allow as many as 64 people to play on networked computers. Instructors can easily modify or create scenarios, monitor training, and jump in and change the direction of the game at any time.
Participants serve as either role-players or evaluators. Their tasks and experiences vary according to their role.
Elaine says DARPA came to her seeking help in building the new game after it became aware of the one she developed for the US Army Special Forces. DARPA already had a training game in the works designed by BBN Technologies. That game had a strong kinetic focus on physical aspects that could go wrong, such as improvised explosive devices going off or a convoy being ambushed.
“DARPA also wanted a nonkinetic adaptive thinking piece for the soldiers, to learn how to negotiate with tribal leaders, for example,” Elaine says. “When things go wrong, troops have to learn to shift how they think in environments that are potentially dangerous.”
A major enhancement made by Elaine to the existing DARPA system was the addition of a peer/expert evaluation element, she says.
“I found Elaine’s idea of using a set of soldiers as observers and assessors particularly innovative and hope the Army can adopt it with its digital training tools,” says Ralph Chatham, former DARPA program manager who selected Elaine to work on the project. “The Army is the only big organization in the world that has institutionalized introspection in their after-action review process [AAR]. Sergeants can talk back to lieutenants in an AAR, and both are pleased with the process. That part of the ATL [Adaptive Thinking and Leadership] simulation game Elaine and the team produced fits the Army perfectly.”
Elaine estimates that the number of people who could be trained with the DARPA-sponsored game could be “huge.” PEO-STRI is putting the nonkinetic modules on its website where it will be available free to all US military services and government.
The nonkinetic modules are comprised of a socio-cultural overlay for a geographical area that is linked to key events and roles of host nation civilians.
Team members who contributed to designing the roles include subject-matter experts from the Fort Lewis Battle Command Training Center in Fort Lewis, Wash.; Pravin Rajan, a US Marine (formerly 6724); and Alan Rolli, former US Army (6341). Elaine says that creating a serious game is “truly a collaborative effort that often involves pulling together a distributed, virtual team of industry, military, and government partners, just to name a few.” Game design teams often represent diverse cultural orientations and face the same challenges encountered by trainees.“We hope this training will help soldiers better understand the cultural environments they are exposed to and better handle difficult situations,” Elaine says. -- Chris Burroughs
The belief among some archeologists that Europeans introduced alcohol to the Indians of the American Southwest may be faulty.
Ancient and modern potsherds collected by New Mexico state archeologist Glenna Dean, in conjunction with analyses by Sandia researcher Ted Borek (1822), open the possibility that food or beverages made from fermenting corn were consumed by native inhabitants centuries before the Spanish arrived.
Dean, who conducted her research through her small business Archeobotanical Services, says, “There’s been an artificial construct among archeologists working in New Mexico that no one had alcohol here until the Spanish brought grapes and wine. That’s so counterintuitive. It doesn’t make sense to me as a social scientist that New Mexico would have been an island in pre-Columbian times. By this reasoning, ancestral Puebloans would have been the only ones in the Southwest not to know about fermentation.”
Not only does historical evidence for fermented beverages exist for surrounding native groups, but people around the world have found ways to alter their consciousness, she says: “Wild yeast blows everywhere.” In the Middle Ages in Europe, “Everyone drank ale because the fermentation purified water.” Egyptian tombs contained loaves of bread “that we used to assume were to eat, but they’re actually dry beer: put bread in water, you get beer.”
Closer to home, the Tarahumara Indians in northern Mexico to this day drink a weak beer called tiswin, made by fermenting corn kernels.
Could ancestral Puebloan farmers — whose ancient mud and rock homes have been found in New Mexico, Arizona, Utah, and Colorado — have done the same?
To check her hypothesis, Dean presented Ted with three types of samples: pots in which she herself brewed tiswin, brewing pots used by Tarahumara Indians, and potsherds from 800-year-old settlements in central New Mexico. The question: Would analysis support the idea that ancient farmers enhanced their nutrition — and perhaps enjoyment of foods — by manipulating wild yeast and corn mixtures centuries before Columbus arrived?
Ted, working under a Sandia program that permits limited use of Sandia tools to aid local small businesses, used gas chromatography and mass spectrometry (rather than destructive solvents) to analyze vapors produced by mild heating of the pot samples.
From Dean’s pots, Ted developed a profile of gases emitted from a known tiswin source. Then he examined Tarahumaran pots to see whether the gaseous profiles corresponded. Finally he examined potsherds that had been buried for centuries to see if the obviously weakened fumes would match, in kind if not in volume, his previous two samples.
Comparing peaks across the three data sets showed the presence of similar organic species, Ted says, though more work must be done before positive conclusions can be drawn.
“We see similarities. We have not found that ‘smoking gun’ that definitely provides evidence of intentional fermentation. It’s always possible that corn fermented in a pot without the intent of the owner,” he says, “and that it wasn’t meant to be drunk.”
Analysis is now underway to highlight patterns of organic species that might provide a more definite, intentional result.
“There appear to be consistencies across the modern home brew and Tarahumara pots,” Borek says. “We are currently examining all data to look for markers that would indicate intentional fermentation occurred on archeological articles.”
The work opens new, unexpected doors, he says, for understanding the human past by means of gas chromatography and mass spectrometry.
Curt Mowry (1822) is examining data and comparing all sets across the provided references, Tarahumara, and ancient samples.
The equipment used in this study is commercially available hardware, modified by Sandia to investigate traces of organic materials in the ambient air of the Washington, D.C., Metro system and on weapon components and materials.
The results were presented by Ted in a talk at the Materials Research Society fall meeting in Boston last week. -- Neal Singer