Do you remember the Shoemaker-Levi fuss a little while ago? Well, it may not seem so, but it is a full five years to the very day since the first fragment of the comet, affectionately known as S-L 9, collided with the planet Jupiter. A spectacular extravaganza for astronomers, amateur and professional alike, continued during the following week.
Comet Shoemaker-Levi took its name from the two American astronomers, Carolyn Shoemaker and David Levy, who discovered it just a year before it crashed. But even then, it was obvious that the comet was in serious trouble. Some years previously it had already approached too close to Jupiter, and the gravitational forces of the giant planet had ripped the comet apart. On its final approach it consisted of 22 individual fragments, strung out like beads on a necklace and all whizzing along in separate, slightly divergent paths, on collision course with Jupiter. They were named after the letters of the alphabet, the first to land being A, the second B, and so on up to T, U, V.
The fragments varied greatly in their size and impact. But even the smaller ones unleashed explosive energy equivalent to millions of megatons of TNT as they crashed into Jupiter's atmosphere at over 150,000 miles per hour in the days following July 16th, 1994.
The most spectacular activity was on a part of the planet just hidden from the Earth, but the rapidly rotating Jupiter quickly swung the affected sites into clear view, and even amateur astronomers with telescopes less powerful than those of their professional colleagues were able to detect clearly that something very strange was going on. And scientists were fortunate in due course to receive images of the actual impacts from a camera on the other side of Jupiter; the American space probe Galileo had been launched towards Jupiter in 1989, long before S-L 9 was ever heard of, and during that fateful week, coincidentally, it was near its destination, ideally placed to record precisely what was going on.
The cataclysmic events of that week in 1994 were the experience of a lifetime for those who were privileged to watch them. Spectroscopic analysis of the huge fireballs also provided much valuable information about the structure of the Jovian atmosphere. But they also had an impact here on Earth. Disturbed by these awesome happenings, the US Congress began to wonder if there was any possibility of something similar occurring here, and formally asked NASA "to catalogue and track any major comets or asteroids that may cross the path of Earth" - a task that is still very much in hand.