Alternative History
Shoemaker-Levy 9 on 1994-05-17

Comet Shoemaker-Levy 9 (SL9, formally designated D/1993 F2) was discovered by astronomers Carolyn and Eugene M. Shoemaker and David Levy. Shoemaker-Levy 9 was located on the night of March 24, 1993, in a photograph taken with the 0.4 metre Schmidt telescope at the Palomar Observatory in California. It was the first comet observed to be orbiting a planet, Jupiter.

In July 1992, the orbit of Shoemaker-Levy 9 passed within Jupiter's Roche limit, and Jupiter's tidal forces acted to pull the comet apart. SL9 was later observed as a series of fragments ranging up to 10+ km in diameter. Some of these fragments collided with Jupiter's southern hemisphere between July 16 and July 22, 1994, at a speed of approximately 60 km per second. The prominent scars from the impacts were more easily visible than the Great Red Spot and persisted for many months. Three fragments, however, escaped Jupiter's gravity. They are designated SL9-A, SL9-B, SL9-C, SL9-D, SL9-E, SL9-F, and SL9-G.

On the night of July 16th, 1994 SL9-G (approximately six km wide) collides with Callisto, because after being shot of Jupiter's range, it was flew away through Jupiter's "fire line," making it hit Callisto. The others are still speeding away, though SL9-E is thrown to Saturn after being effected by Ganymede's gravity.

After passing the Earth, SL9-B, SL9-A, SL9-C , SL9-F and SL9-D pass around the Sun, and speed back to the terrestrial planets. On the way, SL9-F (about eight km wide) slams into Mercury, creating a crater. SL9-D (about 16 km wide) is directed into Venus's orbit, and break into three fragments, SL9-D1, SL9-D2, and SL9-D3. Except for SL9-D2, they crash into Venus's surface and unveil its surface for a few days. SL9-D2 (4.142 km wide) is broken into a ring which is slowly absorbed into Venus's rapidly cooling surface. Venus has cooled significantly, its rotation has sped up, and it has many new craters. Many breakthroughs with Venus are discovered.

Meanwhile, SL9-E (23 Km in diameter) is still speeding directly towards Saturn. The other comets pass Earth, but SL9-A (about five km wide) enters into orbit around Earth, rapidly dropping. Though its diameter has dropped to around 0.6 km, on the 18th of October 1995 SL9-B impacts Antarctica in the Marie Byrd land. SL9-B and SL9-C were moved by Earth's gravity and are heading towards the Red Planet.

SL9-A melts through the ice cap in less than ten seconds and digs a crater eight km wide, the flash heat from the impact melts the surrounding surface ice to a width of 150 km and to a maximum depth of 0.6 km. The impact also causes two sub-ice volcanoes to erupt, these melt more ice. The water created measured approximately 270 cu km. The water washed across the continent and into the surrounding seas, some of the water made its way down to the base of the ice shelves, the water lubricated the glaciers of Antarctica causing them to flow slightly more quickly into the southern ocean.

Due to the location of the impact and the fact that it impacted into two km of ice the dust clouds from the impact do not effect the northern hemisphere, in the southern hemisphere the only noticable difference is a 0.09 degree reduction in temperture for one month and an increase rainfall for one year due to all the vaporized water from the ice falling back to Earth.

At the same time, SL9-B goes into orbit around Mars while SL9-C flies back towards Jupiter. SL9-C's gravity causes Deimos's orbit to ellipse, making it go inside Mars' Roche limit, like Phobos. Eventually, SL9-B crashes into the north pole of Mars, causing the rock and ice to scatter.

SL9-E reaches Saturn. The comet fragment makes it way into a slingshot course to the Inner Planets. However, it passes by Titan which diverts it out of the Solar system. Sl9-C appears to be going to be in a 12 year orbit. After three orbits, it will crash into Jupiter.