Stonehenge's Asteroid Defense Initiative
by D. Trull
As a number of big-budget box office blockbusters have illustrated, it's possible that a giant asteroid or comet could plow into our wonderful little planet someday and obliterate everything that lives on it. One of the many follies of our modern world is that we know this catastrophe can happen, and we've got all kinds of brilliant know-how and powerful resources at our disposal, but we've essentially done nothing to ward off a celestial collision. Instead we devote our technology to creating better weapons, and live nude sex web sites, and movies with really cool special effects.
Now imagine how embarrassing it would be to learn that a primitive civilization in ancient times was more proactive about the risk of massive rocks clobbering the Earth than we are. Boy, wouldn't we look silly then? But that's the startling revelation of an impact hazard expert, who claims to have discovered a 5,000-year-old early warning system designed to forecast the approach of dangerous falling objects from outer space. You may already be familiar with this visionary marvel of prehistoric engineering, which is commonly known by the name Stonehenge.
Yes, it sounds crazy, but this wasn't thought up by some guy who smoked a doobie and rented Deep Impact and Spinal Tap. British astronomer Duncan Steel is one of the world's leading authorities on the threat that near-Earth objects (NEOs) pose to our existence. A resident of Australia, Steel serves as the director of Spaceguard Australia and spent seven years at the helm of the only research program devoted to cataloging and tracking NEOs in the southern hemisphere. (The program was terminated.) Steel is an expert on the Tunguska incident, the crash of a suspected meteor that flattened a remote area in the Siberian wilderness in 1908. He is credited with helping to increase awareness of the impact hazard over the past decade, and wrote a general-audience book on the topic, entitled Rogue Asteroids and Doomsday Comets: The Search for the Million Megaton Menace That Threatens Life on Earth.
This book includes a chapter outlining Steel's speculations on the purpose behind the ancient monuments of Stonehenge. It has long been believed that the megaliths were constructed in alignment with some sort of observed celestial phenomena, such as solstices and equinoxes, but could it actually be doomsday asteroids and meteors that Stonehenge's builders were concerned with documenting?
The primary basis for Steel's astounding hypothesis is the Earth's passage through the Taurid complex, a belt of asteroids and space debris left behind by a giant comet that passed through the solar system 20,000 years ago. The Earth regularly passes near the Taurids, experiencing meteor showers like the celebrated ones that occurred in 1998. But at some times in the past, the Taurids might have provided more than just fireworks, and could have thrown some hugely destructive rocks down at us. By Steel's calculations, the period of greatest danger would have been between 5,000 and 5,500 years ago. That happens to be the same time frame when construction began on Stonehenge. According to Steel, that's no coincidence.
Steel contends that during the time that Taurid asteroids were most likely to pelt the Earth into oblivion, Stonehenge's Heel Stone would have aligned perfectly with the position of Comet Encke, which travels along with the Taurid complex and is one of its most visible indicators. Steel thinks it's just random chance that the Heel Stone also lines up with the sun's position on the summer solstice. He says that the impact warning intent of the monuments' original builders was lost to history, and the Druids and pagans and others who later added to its construction had no idea what the true meaning of Stonehenge was.
Okay, let's assume that Steel is right, and these ancient sages were trying to predict when a mega-asteroid was about to smash into the Earth. What the heck were they gonna do if they ever found one? Try and deflect it away with boulders and a catapult? Throw sticks at it? Or maybe just party like it's 2999 B.C.? Actually, Steel suggests that they had prepared impact shelters in the event of a collision. The Long Barrows, a nearby earthen mound of communal tombs, might have been intended for use as emergency shelters, he believes. The amount of protection a dirt hole is going to offer amidst a full-on planetary upheaval is questionable at best, but I guess it's better than nothing.
So is there any validity to Steel's Stonehenge theory, or has the guy just got rocks in his head? If you think his ideas about ancient asteroid alerts sound silly, you're not alone. The consensus in the field appears to be that Steel is unassailably a top expert on the subject of the NEO impact hazard, but his revisionist history could use some revising. A book reviewer in Sky & Telescope said that Steel's views on Stonehenge in Rogue Asteroids are "fiction, not even science fiction." Another writer on a NASA web site criticized him for not adequately distinguishing his personal speculations from hard science in his writings, confusing things for the non-scientists whom the book was intended for. Clark R. Chapman, writing in the journal Meteoritics & Planet, really let Steel have it with both barrels:
"Eschewing the objective rigor of archaeoastronomy, Steel pictures these ancient monuments as we might perceive elephants and other fantastic shapes among the clouds in the sky. He relies on nothing more substantial than visual metaphor and timing 'coincidences' of plus-or-minus 500 years. Stonehenge seems to be Steel's personal Rorschach test, in which he sees his personal passion -- meteor storms -- writ large."Harsh words, but that might be a reasonable assessment of what makes Duncan Steel tick. Here it should be noted that there's more to his weird speculations than just the Stonehenge stuff. He also theorizes that the pyramids of Egypt were built in response to meteor showers, and he promotes the "neo-catastrophist" musings of Victor Clube, who believes that the course of Western civilization -- including the Dark Ages and the Protestant Reformation -- has been profoundly shaped by the appearance of comets and meteors in the sky. Wild conjectures like this are reminiscent of the starving shipwreck victims you see in cartoons, who hallucinate that any living thing in sight is a giant hot dog or turkey drumstick. When you're really obsessed with something, you can find it anywhere you want to see it.
Chapman noted in his criticism that the notion of a catastrophic impact from outer space has had to work hard to overcome the "Chicken Little giggle factor" and gain widespread acceptance as a very real threat. You'd think the last thing Steel would want is to undermine that credibility with wacky claims about ancient times, and maybe jeopardize our chances of being prepared on the horrible day when the sky really is falling.
Sources: Electronic Telegraph; Southwest Research Institute web site; The Society for Interdisciplinary Studies web site; NASA's Asteroid and Comet Impact Hazard web site.
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