Early on the morning of 1 February 1994, President Clinton, Vice-President Gore, the Joint Chiefs of Staff and the members of the National Security Council were awakened from their sleep by Pentagon officials.footnote A military surveillance satellite had detected the brilliant flash of a nuclear explosion over the western Pacific. There was intense concern that the strategic warheads aboard a Russian or Chinese missile submarine accidentally might have detonated. Military aircraft, however, failed to detect any unusual radiation in the indicated ocean sector, and defence intelligence experts soon concluded that the satellite had actually witnessed the explosion of an asteroid fragment, later estimated to have been the equivalent of a 200-kiloton nuclear blast. The President went back to bed.footnote1

Five months later, beginning on 16 July, hundreds of millions watched in awe as the Hubble space telescope transmitted images of Comet Shoemaker-Levy 9’s fiery death in the dense atmosphere of Jupiter. For nearly a week, the plummeting trail of cometary fragments produced a succession of huge fireballs—equivalent to many million megatons of explosive energy—that left dark, temporary scars on the giant planet. Then, on 9 December 1994, an object comparable to one of Shoemaker-Levy 9’s fragments—the asteroid 1994xmi—approached within 105,000 kilometres of the Earth, a record close call in the brief annals of monitoring so-called Near-Earth Objects (neos).footnote2

These events made 1994 something of a watershed in public awareness of the Earth’s vulnerability to comet and asteroid bombardment.footnote3 Indeed, the spectators at Shoemaker-Levy 9’s immolation were the first generation of humans to observe a major planetary impact since medieval monks recorded the collision of an asteroid with the moon, forming the crater Giordano Bruno, in 1178.footnote4 Congress was sufficiently impressed to fast-track a major study of neo-detection technology and a probe to the asteroid Eros—launched on 16 February.footnote5 Meanwhile, the friends of Star Wars, including H-bomb father Edward Teller, lobbied for an orbital anti-asteroid defence of super-lasers and thermonuclear weapons. (Both of which, as Carl Sagan and others immediately pointed out, could be turned against Saddam Husseins on Earth as easily as neos.)footnote6

Beyond the predictable media hyperbole about exterminators from outer space—so reminiscent of ‘comet hysteria’ throughout human history—the events of 1994 were also an incomparable ‘teach-in’ on the Earth’s citizenship in the solar system. February’s giant fireball over the Pacific, July’s fusillade against Jupiter, and December’s breathtaking near-miss—were all cram sessions in the new Earth science being shaped by comparative planetology and the neo-catastrophist reinterpretation of the stratigraphic record. It is a lesson, of course, that many geologists, as well as geographers and historians, have great difficulty accepting. Even more than plate-tectonics, an ‘open system’ view of the Earth that recognizes the continuum between terrestrial and extra-terrestrial dynamics threatens the Victorian foundations of classical geology. To cite only one example, a single impact event can compress into minutes, even seconds, the equivalent of a million years or more of ‘uniformitarian’ process.

But this is not a mere family feud. The ‘golden age’ of Cold War space exploration, now drawn to a close, has seeded the fields of philosophy with discoveries every bit as strange and revelatory as those of Magellan and Galileo—the names, appropriately enough, of our most recent planetary galleons. I must confess that as an ageing socialist, who spent the glory years of the Apollo program protesting the genocidal bombing of Indochina, it has taken me half a lifetime to warm to a scientific culture incubated within Cold War militarism and technological triumphalism. Yet it is also the contemporary home of luminous and, dare I say, revolutionary attempts to rethink the Earth and evolution within the new context of other planetary histories.