This was published in Nature by Duncan Steel to commemorate the
The fact not mentioned too loudly is that the vast majority of meteorites are stony and clearly capable of the same behavior. The incoming trajectory is likely comparable to a comet like orbital coming from the sun and arriving at speed.
What is important today is that we now know that a rapidly arriving large stony mass will be pulverized as it passes through the atmosphere leading to a massive explosion and heat release. Even without a visible touchdown we have seismic activity.
The big event associated with the Pleistocene nonconformity was vastly larger but that does not mean that the events of
The existence of apparent impact craters in the
I have already pointed out that the location of the disturbance was well situated to release the crust allowing it to settle into today’s configuration. This all requires vastly less kinetic energy than I had previously anticipated and described. Why use a hammer when it appears a tap will do? It was still the mother of all meteoric events during human history.
I had not anticipated a properly timed meteor strike with a flight path rather well aimed to achieve maximum effect. That was calling for a remarkable coincidence without any evidence.
Those readers who have not read my article on the Pleistocene Nonconformity are advised to do so since we tackle the key issue of crustal stickiness there.
It is clear that the risk of meteor striking the earth and causing massive damage is currently underestimated. Piecing together the
This also underlines the need for a global meteorite defense net and the existence of kinetic high orbit missiles able to intercept and disturb a meteor’s path. It need not be overbuilt in order to do its job. It just needs to be available for a one off need every century or so. Our hardware is likely up to the scanning job even now.
The statistical risk is very low but is not zero. The risk that such an event could destroy centers of humanity is also very low but not zero. Integrating a simple defense measure with our ongoing research efforts is a simple method of reducing even those odds. And as we progress in space exploration and exploitation the odds become even longer.
Today our culture is global, thus making a
Duncan Steel // Published online 25 June 2008 | Nature 453, 1157-1159 (2008)
"Sooner or later, it was bound to happen. On June 30, 1908,
So begins Rendezvous with Rama , a 1972 novel by Arthur C. Clarke in which mankind learns the hard way about the dangers posed by incoming asteroids. The 2077 impact in northern
The approximate site of the blast's epicentre is now marked by a totem pole that researchers have dedicated to Agdy, the god of thunder in local mythology. Getting there is quite a trek, but the fascination of the site still draws an intermittent stream of scientists to the remote wilderness about 1000 kilometres north of
That does not mean there was no significant contemporary evidence to bring to bear. Siberia was and is an empty place - but a blast which, had it happened over Chicago, would have been heard from Georgia to the Dakotas, still drew a lot of attention. In the days following the blast, A.V. Voznesenskij, the director of the
In the days after the blast, much of Europe experienced eerie 'bright nights': readers wrote to The Times in
There was, however, one good reason to doubt that a small asteroid was involved: the belief of the time that this would deliver a valuable hunk of iron to the surface. The Russian meteorite hunter Leonid Kulik, who led the first expedition to the epicentre in the 1920s, obtained funding from the Soviet government on the basis that he would find a valuable ore body there. But when he reached his goal in 1927 he found no metal. Nor did he find the crater that an impact was expected to leave. (There are now claims that nearby
Other explanations were even more far fetched than candyfloss comets. Soviet science-fiction author Alexander Kazantsev realized, as Shapley had, that the best explanation involved an explosion at altitude, and suggested in 1946 that a nuclear-powered alien spaceship exploding just before landing might have been the culprit, an idea taken up eagerly and earnestly in the following decades.
A more scientifically promising possibility was naturally occurring antimatter, a suggestion made independently by various people at various times. In 1940, Vladimir Rojansky of
More than a decade later, Philip Wyatt, a graduate student at
This notion was expanded on by three eminent American scientists (including 1960 Nobel Prize winner Willard Libby and
Even more extreme, in 1973 two University of
Another approach has been to suggest that, despite the straightforward implications of eyewitness accounts of a bright object zipping across the sky, the source of the blast was in fact beneath the surface. A recent example is a claim that it was due to a 10-million-tonne belch of methane that subsequently exploded high in the sky. Others see a geophysical source involving peculiar tectonic behaviour.
The fact that such ideas were entertained (and still are, in some circles) speaks both of a certain fascination with the fanciful and the abiding need to explain that confusing lack of a crater. The fact that, by the 1960s, various craters around the world had been accepted as meteorite strikes meant that the anomalous lack seemed all the more confusing. In 1993 that confusion was allayed, at least for most people, by Chris Chyba, Kevin Zahnle and Paul Thomas. With the help of computer simulations derived from nuclear weapons' tests they showed that a solid, stony object about 50 metres across - the most likely sort of thing in that size range to hit the Earth - would not be expected to reach the ground. There was no need to invoke weirdly low cometary densities - at the relevant speeds the shock wave generated within a solid body as it slams into the atmosphere would rip up an everyday rock just fine. Formations such as Meteor Crater in
A similar explanation was arrived at by Jack Hills, working at Los Alamos National Laboratory in New Mexico with Patrick Goda, and both teams had been to some extent pre-empted by a Soviet team led by V.P. Korobeinikov, the work of which had not been widely appreciated in the West. These various models led to an estimate that the blast was equivalent to about 15 megatonnes of high explosive - bigger than all but the very largest thermonuclear weapons. However, work by Boslough indicates that the energy required to fit the observed phenomena could be rather less, around 3 to 5 megatonnes.
That analysis assumes that the impactor was a stony asteroid - but a comet is still a possibility. In 1978, L'ubor Kresák suggested the
The question of what the object was is not purely academic. If
In Rendezvous with Rama, Clarke's solution to the threat of impacts was an asteroid search programme aimed at ensuring that such a catastrophe could never occur again: he called it Project Spaceguard. This became the name of a real-life programme, and that search continues. But 50-metre objects are too small to spot far in advance of their impact. So although another
Duncan Steel is an astronomer and writer after whom Arthur C. Clarke once named a robot.
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