This is a composite photo, assembled from separate images of Jupiter and comet Shoemaker-Levy 9, as imaged by the NASA/ESA Hubble Space Telescope in 1994.
Comet Shoemaker-Levy 9 was discovered by astronomers Carolyn and Eugene M. Shoemaker and David Levy on March 24, 1993. It was the first comet observed to be orbiting a planet -- in this case, Jupiter -- rather than the sun. The effect of Jupiter's tidal forces had already torn the celestial body apart and, eventually, the fragments collided with Jupiter between July 16 and 22, 1994.
The image of the comet, showing 21 fragments, was taken on May 17, 1994. The image of Jupiter was taken on May 18, 1994. The dark spot on the planet is the shadow of the inner moon lo. The apparent angular size of Jupiter relative to the comet, and its angular separation from the comet when the images were taken, have been modified for illustration purposes.