Shoemaker-Levy 9: Fragment W (12 Images)
Date: 22 Jul 1994
These 12 images of Jupiter and the luminous night-side impact of fragment W of Comet Shoemaker-Levy 9 were taken by the Galileo spacecraft on July 22, 1994. Reading from left to right in each row from the top, they present a 30-second history of the initial phase of the impact event.
The images were taken starting at 8:06:10 Universal Time, at intervals of 2.3 seconds. Times are those at which an Earth-based observer would have seen the same event. Because of the way the images were taken, the 5th and 6th images are 7 seconds apart. These time-lapse images have been selected from 152 that were returned to Earth of the more than 1800 that were taken to ensure catching the event. They have been processed to remove radiation noise and to enhance contrast.
In the first two images, no event is seen. Then, in the 3rd image at 8:06:14 UT, a spot appears on Jupiter's dark side, just off the terminator, at about 43 degrees S latitude. The event reaches peak brightness (about that of a 1st-magnitude star) in the 4th image and then fades over the next 7 images.
We interpret the initial flash as the bolide phase of the impact, like the flash seen when meteors hit Earth's atmosphere. This flash lasted only a few seconds and evolved into a fireball explosion, which was rather weak in the case of W. The luminosity of the explosion phase is seen weakly in images 6 through 11 of this series. By the 12th image, at 8:06:40, the fireball is no longer visible. (Of course, Hubble captured excellent pictures of the rising W plume, and Earth-based astronomers using heat-sensitive infrared detectors, observed the later phases of the explosion that were no longer radiating in visible light.)