A mosaic of HST images (top) portrays almost the full extent of Comet Shoemaker-Levy 9 as it appeared in late January 1994. The train of fragments gradually lengthened, each separate piece following its individual orbit around Jupiter. Here it is almost 640,000 kilometers (400,000 miles) long. Each fragment is like a small comet with a nucleus, surrounded by a hazy coma, and its own tail.
Most of the fragments lie in a straight line, but several are clearly off the main train. These were probably formed when larger fragments from the original disintegration broke up again into smaller pieces, perhaps because they were spinning too fast to hold together, or because a pocket of gas erupted.
The three lower images show how one group of fragments broke up further and altered over a period of eight months. Formally named fragments P and Q, astronomers nicknamed them 'the gang of four' when it became clear that both were double.
In the image taken on July 1, 1993, before the optics of HST were corrected by the Servicing Mission (left), the double nature of the two bright nuclei is just detectable. With the new camera in operation, the image taken on January 24, 1994 (center) is sharper, and the two pairs of nuclei have also moved apart. By March 30, 1994 (right), the left-hand fragment of the lower pair has faded to a loose puff of dust. Meanwhile, the right-hand one has split into two, though only one of these survived to impact Jupiter in July 1994.
Camera: Top: WFPC2, mosaic of two images
from WF components and one image from PC component. Lower left.. WF/PC-1.
Lower center and right.. WFPC2.
Technical Information: Images shown in
false color to distinguish different intensities of light.
Credit: H. A. Weaver and T. E. Smith (STSCI),
and NASA
