In July 1994 the Hubble Space Telescope, orbiting 600 kilometres above Earth, and hundreds of thousands of telescopes around the world were aimed at Jupiter to watch the celestial drama of the century. Never in history had anyone witnessed the cataclysmic collision of two worlds, a comet crashing into a planet.
A few days before the crash, the observers noticed a trail of 21 comet pieces stretching for a length of more than 5 million kilometres, more than twelve times the distance between the Earth and the Moon. On 16 July 1994, the first piece with a width of 1 kilometre - the puniest in the line-up - slammed into Jupiter. Over the next six days twenty more pieces hit the giant planet.
When plunged into Jupiter's visible clouds each piece of S-L 9 was travelling with a speed of 200,000 kilometres per hour. As the piece entered the denser atmosphere it flattened like a pancake and then disintegrated, dumping energy equivalent to a blast of more than a million megatons (explosive energy is measured in kilotons or megatons; 1 kiloton equals 1,000 tonnes and 1 megaton 1 million tonnes of high explosive TNT). Taken all together, the 21 fragments released about 40 million megatons of explosive energy. Compare this energy with the Hiroshima atomic bomb: the mere 15-kiloton blast killed 140,000 people, injured hundreds of thousands and destroyed 70,000 buildings. The largest hydrogen bomb ever tested was a 58-megaton Russian bomb in 1961. A 40-million-megaton blast defies comprehension.
The explosion expelled the atmosphere into bright plumes of gas and debris, which at their peak towered 2,200 kilometres above the clouds. After a few minutes the plume plunged back into the atmosphere. The collapsing plume and the underlying atmosphere became hot and started releasing great fireballs of infrared rays. The point of impact turned into a dark scar, dubbed 'black eye' by astronomers, thousands of kilometres across.
This scary scenario was repeated twenty times, every seven hours, on average. The 'string of pearls' had been reduced to a chain of smouldering scars girdling the planet. Some fragments created bigger bangs than others. The largest of the fragments, a solid body 3 kilometres across, left a 'black eye' of debris as large as the Earth. Some of the black eyes took months to fade from Jupiter's face.
The diameter of Jupiter is eleven times greater than that of Earth; a piece of S-L 9 was only about a kilometre wide. Had it struck Earth it would have gouged a crater 60 kilometres across. Comparing S-L 9 with Jupiter is like comparing a fly with a dinosaur. If such a puny crash could cause so much damage, what would happen if a large comet hit Earth?
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