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The Shoemaker-Levy 9/Jupiter Impact
Named for its discoverers Eugene Shoemaker, the discoverer of many comets, and David Levy, his colleague and co-worker, the comet was first spotted in 1993.
Perhaps this section should be called "The Shoemaker-Levy 9/ Jupiter impacts," because at least 20 large fragments of the comet, accelerating at 60 kph, hit the planet. The results were spectacular. Plumes rose thousands of kilometers above the cloud level. Fireballs scudded along the cloud layers. Enormous rifts were created on the surface and giant gas bubbles were left in the atmosphere.
The twenty odd fragments all had unique impacts. Some left canyons, others no visible trace of their passing. This was partially due to their size: the largest fragments had two-kilometer diameters.
The first fragment, Fragment A, hit Jupiter with the force of a quarter million megatons of TNT, leaving a plume 1000 km above the atmosphere. The effects were visible from Earth-based telescopes.
Fragment B came in like a lion but left like a lamb. Though the approximate brightness as its predecessor, its impact left a small mark, barely observed.
Fragments C, D, and E were all blockbusters, leaving plumes and fireballs in the spirit of Fragment A.
Fragment F was cast from Fragment B's mold. No discernable impact.
Fragment G was the most phenomenal of all. Its three-kilometer length hit Jupiter with the energy equivalent of 6 quadrillion tons of TNT--600 times the estimated punch of the world's conventional and nuclear arsenal. Fragment G's fireball rose 3,000 km above the atmosphere, nearly triple that of its nearest competitors.
After Fragment G hit, it was difficult to seperate the effects of successive impacts. These later fragments hit near the original impacts, leading to confused results. Of the successors, though, Fragments N, P2, Q2, T, U, and V were nearly undiscernable, while Fragments A, C, D, E, H, Q1, R, S, and W left scars an Earth radius long and Fragments K and L left scars an Earth diameter long.
If even one average-sized fragment from the comet had hit Earth, life as we know it would have been imperiled. If, for example, Fragment G had hit the Earth, it is likely that little above the bacterial level would have survived. The debris knocked off of the Earth might eventually form another moon, or another planet.