A Comet Impacts a Planet

Except for seeing meteors enter our atmosphere, no contemporary astronomer had ever observed an impact on another world until 1994. Comet Shoemaker–Levy 9, S-L 9, was discovered in March 1993 by astronomers Eugene and Carolyn Shoemaker and David Levy. Carolyn’s first impression of the discovery photo was it “looked like a squashed comet.” This description was due to the fact that the comet had been broken apart by the gravitational pull of Jupiter. The largest cometary fragment was 2 kilometers or 1.2 miles across.

A NASA Hubble Space Telescope (HST) image of comet Shoemaker-Levy 9, taken on May 17, 1994, with the Wide Field Planetary Camera 2 (WFPC2) in wide field mode. When the comet was observed, its 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. 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.
Public Domain | Image courtesy of NASA.

After determining the comet’s orbit, it was found that Shoemaker–Levy 9 fragments would impact Jupiter over several days, 22-26 July 1994. The question became if the impacts would be visible to astronomers and orbiting satellites, like the Hubble Space Telescope.

Over the five-day period, twenty-one (21) distinct impacts were observed by satellites like the Hubble Space Telescope, as well as Earth-based telescopes. Fireballs resembling an atomic bomb mushroom cloud were seen at Jupiter’s horizon. Dark spots were seen in the upper atmosphere of Jupiter after impact; these were visible even in small amateur telescopes. Some of these spots were as big as Earth. The black impact features were visible on Jupiter for months; some likened them to a black eye. Due to the S-L 9 series of impacts, astronomers were better able to explain rows or chains of craters found on the Moon and other objects, like Jupiter’s moon Ganymede.

Image of Jupiter exhibiting some of the Shoemaker–Levy 9 fragment impact sites as black spots.
NASA Hubble Space TelescopePublic Domain | Image courtesy of NASA.

Image of Jupiter’s ‘black eye’ G fragment impact site.
NASA Hubble Space TelescopePublic Domain | Image courtesy of NASA.

Image of A chain of craters on Jupiter’s moon Ganymede that would have been caused by a series of comet fragments like Comet Shoemaker-Levy 9.
NASA Galileo SpacecraftPublic Domain | Image courtesy of NASA.