Tunguska Centennial

Today is the 100th anniversary of the Tunguska Event, a massive explosion in the Siberian wilderness whose cause remained a mystery for most of the twentieth century. The explosion flattened eighty million trees over an 800-square-mile area, but left no discernible impact crater. The remoteness of the site impeded research into the origins of the explosion, and Soviet scientific findings diffused only gradually into the West. Consequently, astrophysicists, earth scientists, science fiction writers, and random crackpots developed a variety of hypotheses about the explosion - that it was caused by a comet, a chunk of interstellar antimatter, a quantum black hole (a popular hypothesis among sci fi writers), or a malfunctioning alien spacecraft. In the 1950s and '60s, however, Soviet researchers discovered microscopic glass nodules in soil samples from the site; the nodules contained high levels of nickel and iridium, both telltale markers of an asteroid. It seems likely, therefore, that the explosion was produced by a meteor - a small (20-30 meters) asteroid or a fragment of one - exploding in the air above the Tunguska River basin.

I don't usually direct readers to Wikipedia, but the entry on the Tunguska event appears judicious; it includes several firsthand accounts of the explosion from observers, a careful weighing of causal hypotheses, and the observation that these sorts of midair meteor explosions are actually rather common - but they generally occur over the ocean, where (until the advent of earth-observation satellites) there haven't been many witnesses.

While we're on the subject of asteroids intercepting the earth, we may note that Greg Easterbrook isn't the only person worried about the consequences of a large meteor impact in the near future. The U.S. House of Representatives just passed a bill (HR 6063) which, among other provisions, directs NASA to plan an unmanned monitoring expedition to the Apophis asteroid (which will pass uncomfortably near the Earth in 2029) and the White House Office of Science and Technology Policy to develop an asteroid-deflection strategy. The bill didn't estimate the cost of the program, but I can't imagine it will cost more than, say, a week or two of the Iraq War. No mention of any role for Bruce Willis, either, but he's still got 21 years to wait for the phone to ring.

The Premier's Little Green Book

Some pleasant, if peculiar news from the latest issue of Time Magazine (June 30, 2008): last November the prime minister of the People's Republic of China, Wen Jinbao, identified the Meditations of Marcus Aurelius as one of his favorite books, claiming "to have read [it] nearly 100 times." Since then, the Meditations have become a bestseller in China, rising to fifth place in the China Book International bestseller list. This was welcome news, since I've long found Aurelius's work to be a source of reassurance, ever since I bought my first copy of it (the green-covered Loeb Classical Library edition) during my first week in college. It's nice to know that millions more people are discovering it for the first time. Yet I can also see why the book would resonate with the leadership of an authoritarian state which is trying, not always successfully, to promote social harmony in the midst of the largest economic revolution in history. Marcus Aurelius tells his readers that human relationships are naturally harmonious and beneficial, and human misconduct both involuntary and transitory. "With what art thou discontented? The wickedness of men? Take this conclusion to heart, that rational creatures have been made for one another, that forbearance is part of justice, that wrongdoing is involuntary, and think how many ere now, after passing their lives in implacable enmity, suspicion, hatred...have been laid out and burnt to ashes - think of this, I say, and stay thy fretting." (IV.3, trans. by C.R. Haines)

Cultural Exchange

Here's a brief anecdote from the first voyage of John Davis, the 16th-century English explorer to whom I referred in my post of May 31st: when Davis first landed on the coast of Greenland in late July 1585, he encountered a large party of Inuit, who approached Davis's ship in ten canoes. Rather than attacking or kidnapping the Greenlanders (that would occur on his second voyage), Davis instead urged his crewmen to use their "best policy to gain their friendship." That policy included music: as the canoemen approached, Davis and his officers "caused our musicians to play, ourselves dancing and making many signs of friendship." For the rest of the day, the two groups of strangers pantomimed one another's gestures, shook hands, and exchanged gifts of clothing. The next day (30 July 1585), one of the Inuit returned Davis's initial favor: he climbed a rock, displayed "a thing like a timbrel, which he did beat upon with a stick, making a noise like a small drum," and danced. (Albert Markham, ed., Voyages and Works of John Davis, Navigator [London, 1880], 7-8.) Regrettably, we have no record of any subsequent attempts to create an Elizabethan/Eskimo fusion musical style.

Your Monthly Apocalypse

Many of us think of large meteor strikes, like the one which formed Quebec's Manicouagan Reservoir (pictured left, as seen from low earth orbit), as events that occur in geological time - that is, many tens of thousands of years, if not many millions of years ago. The possibility of such an event occurring in our lifetimes, outside of a movie theater at least, seems remote. In a new article in The Atlantic, however, Greg Easterbrook suggests that the danger of a large (1+ kilometers) asteroid hitting the earth in the near future is actually fairly high. He observes that in the last 25 years astronomers have found several thousand more near-earth asteroids than they expected, and that several geologists, notably Dallas Abbott of Columbia, have found evidence of many more terrestrial meteor strikes than they expected - mainly by looking for craters in the ocean floor and elevated iridium levels in the soil. (Iridium is an element commonly found in asteroids but relatively scarce on earth.) Some of these strikes are quite recent: a 300-meter asteroid apparently impacted in the Gulf of Carpentaria off northern Australia in 536 AD, leading to cold temperatures and crop failures for the next couple of years. Another asteroid hit the western Indian Ocean around 2800 BC, producing tsunamis and severe flooding and perhaps contributing to the Mesopotamian and Biblical flood myths. And several researchers from the Lawrence Berkeley National Laboratory believe, based on elevated soot and iridium levels in the soil, that 1 or 2 large meteors exploded in the air over North America about 12,900 years ago, causing climatic stress that may have contributed to the decline of the Clovis Paleo-Indian culture and the extinction of the wooly mammoth, along with most other large mammals in North America. These are all quite recent findings, and there are sure to be more.

Easterbrook believes that the odds of another large asteroid strike in the next century are probably 1 in 10, and that the results will be predictably catastrophic. An ocean impact will produce tsunamis and destroy coastal cities; a land impact will generate huge dust clouds and intense acid rain; both will lead to hard winters and possibly a mini-ice-age. He also believes that it is well within the capability of human beings to prevent such a disaster from happening: assuming astronomers can detect an incoming asteroid (a big assumption, but feasible), the United States or another spacefaring country could simply launch a "gravitational tractor," a large probe which would match the asteroid's velocity and use its own tiny natural gravitational force to deflect the asteroid from its earth-intercepting trajectory. The probe would not have to be manned, but I suppose it could be - it would be nice to give Bruce Willis something to do in his dotage. At any rate, NASA is reluctant to devote any of its scarce resources to asteroid defense, which is considers too science-fictional, and prefers to concentrate instead on practical and down-to-earth projects, like a Moonbase.