Above is a Hubble Space Telescope (HST) image of comet Shoemaker-Levy 9, taken on May 17th, 1994, with the Wide Field Planetary Camera 2 (WFPC2) in wide field mode. When observed, the comet's train of 21 icy fragments stretched across 1.1 million km (710 thousand miles) of space, or 3 times the distance between Earth and the Moon. This required 6 WFPC exposures spaced along the comet train to include all the nuclei. The image was taken in red light and has been informally nicknamed the "string of pearls." The comet was approximately 660 million km (410 million miles) from Earth when the picture was taken, on a mid-July collision course with the gas-giant planet Jupiter. Image Credit: NASA, ESA, and H. Weaver and E. Smith (STScI)
Comet Shoemaker–Levy 9 (formally designated D/1993 F2) was discovered by American astronomers Carolyn and Eugene M. Shoemaker and David Levy. Shoemaker–Levy 9 was orbiting Jupiter and at that time was located on the night of March 24th, 1993, in a photograph taken with the 40 centimeter (1 ft 4 in) Schmidt telescope at the Palomar Observatory in California. Named as the nineth jointly discovered by the trio, it was the first comet observed to be orbiting a planet, and had probably been captured by the planet around 20 to 30 years earlier.
On July 8th, 1992, Comet Shoemaker–Levy 9 passed within Jupiter's Roche limit, and Jupiter's tidal forces pulled the comet body apart. The comet was later observed as a series of fragments ranging up to 2 km (1.2 mi) in diameter. These fragments collided with Jupiter's southern hemisphere between July 16th and July 22nd, 1994, at a speed of approximately 60 km/s (37 mi/s) or 21600km/hr (13320m/hr). The prominent scars from the impacts were more easily visible than the Great Red Spot and persisted for many months.
To learn more about the history and the legacy of Comet Shoemaker-Levy 9, visit this URL: www2.jpl.nasa.gov/sl9/