the submersible dirigible

I generally enjoy much of what The Atlantic publishes, but Gregg Easterbrook’s feature article last month regarding the delights of our solar system, especially near earth objects, was especially delightful. We’ve all heard a great deal about humanity’s untimely demise at the hands of an errant asteroid from the likes of Bruce Willis and Morgan Freeman, but the threat has always seemed too abstract, too existential to really resonate.  Reading about the 1908 Tunguska Event for the first time a few months ago, and more recently enjoying Easterbrook’s Atlantic article, these issues started to come into more focus.  Wikipedia provides this helpful summary of the Tunguska Event:

The explosion was most likely caused by the air burst of a large meteoroid or comet fragment at an altitude of 5-10 kilometres (3-6 miles) above Earth’s surface. Different studies have yielded varying estimates for the object’s size, with general agreement that it was a few tens of metres across.

Although the meteor or comet burst in the air rather than directly hitting the surface, this event is still referred to as an impact. Estimates of the energy of the blast range from 5 megatons to as high as 30 megatons of TNT, with 10-15 megatons the most likely - about 1000 times as powerful as the bomb dropped on Hiroshima, Japan and about one third the power of Tsar Bomba.

Easterbrook’s Atlantic article notes, “had the explosion occurred above London or Paris, the city would no longer exist.”  Delightful!  While the 1908 air burst over Siberia is certainly chilling, another possible (relatively recent) asteroid impact is even more shocking.

Abbott believes that a space object about 300 meters in diameter hit the Gulf of Carpentaria, north of Australia, in 536 A.D. An object that size, striking at up to 50,000 miles per hour, could release as much energy as 1,000 nuclear bombs. Debris, dust, and gases thrown into the atmosphere by the impact would have blocked sunlight, temporarily cooling the planet—and indeed, contemporaneous accounts describe dim skies, cold summers, and poor harvests in 536 and 537. “A most dread portent took place,” the Byzantine historian Procopius wrote of 536; the sun “gave forth its light without brightness.” Frost reportedly covered China in the summertime. Still, the harm was mitigated by the ocean impact. When a space object strikes land, it kicks up more dust and debris, increasing the global-cooling effect; at the same time, the combination of shock waves and extreme heating at the point of impact generates nitric and nitrous acids, producing rain as corrosive as battery acid. If the Gulf of Carpentaria object were to strike Miami today, most of the city would be leveled, and the atmospheric effects could trigger crop failures around the world.

What’s more, the Gulf of Carpentaria object was a skipping stone compared with an object that Abbott thinks whammed into the Indian Ocean near Madagascar some 4,800 years ago, or about 2,800 B.C. Researchers generally assume that a space object a kilometer or more across would cause significant global harm: widespread destruction, severe acid rain, and dust storms that would darken the world’s skies for decades. The object that hit the Indian Ocean was three to five kilometers across, Abbott believes, and caused a tsunami in the Pacific 600 feet high—many times higher than the 2004 tsunami that struck Southeast Asia. Ancient texts such as Genesis and the Epic of Gilgamesh support her conjecture, describing an unspeakable planetary flood in roughly the same time period. If the Indian Ocean object were to hit the sea now, many of the world’s coastal cities could be flattened. If it were to hit land, much of a continent would be leveled; years of winter and mass starvation would ensue.

I’m not entirely sure why I’m obsessed with space-based articles recently.  I hope to share mostly music here, but occasionally I can’t resist drifting off focus if I’ve recently been reading material even more compelling than Machinefabriek’s 13th 3″ cdr release of the year.

Best of all, Easterbrook’s article ends on a high note.  After explaining at length the horrible danger of asteroids, he casually concedes, “But when it comes to killer comets, you’ll just have to lose sleep over the possibility of their approach; there are no proposals for what to do about them… because many comets change course when the sun heats their sides and causes their frozen gases to expand, deflecting or destroying them poses technical problems to which there are no ready solutions.”

Another more dramatic simulation of an asteroid strike is included below the fold.  The simulation below is more cinematic, but really nothing to worry about. As Easterbrook reminds us, those relatively small (and relatively common) objects — like the 30m Tunguska Event asteroid — are our real concern.

Continue reading ‘The Sky Is Falling’