Jupiter has been in the news a lot lately, with the Juno spacecraft continuing to send back stunning new images of the largest planet in the Solar System, including close-ups of the Great Red Spot. But something else happened at this time 23 years ago which captured astronomers’ and the public’s attention – a huge explosion in Jupiter’s atmosphere as a comet broke apart and the fragments collided with the planet, plummeting into the deep, thick atmosphere. The impacts and resulting “scars” were observed by telescopes around the world.
The collision created a spectacular show, easily observed by both large observatories and smaller telescopes alike. Comet Shoemaker-Levy 9 had first been captured by Jupiter’s gravity about 20-30 years earlier, and in July 1994 finally came too close to the planet and was broken apart into multiple fragments which then collided with the planet one after another. The first impact was on July 16, 1994; the resulting explosions were equivalent to 6,000,000 megatons of TNT, producing a fireball larger than Earth, with a temperature of about 24,000 K. A total of 21 impacts were seen over the next six days. The largest impact, from fragment G, created a huge dark spot over 12,000 kilometres (7,456 miles) across, and released an enormous amount of energy – equivalent to 6,000,000 megatons of TNT (600 times the total nuclear arsenal of the world at the time). After the largest impacts, powerful shock waves were observed in the atmosphere moving at speeds of 450 metres/second (1,476 feet/second).
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