On this date in 1994 the first fragment of Comet Shoemaker-Levy 9 crashed into the giant planet Jupiter followed by many more over the next five days. This was the first time that a collision between a comet and a planet has been observed. There were at least 21 fragments with sizes up to two kilometres in width.
Hubble Space Telescope image of impact sites on Jupiter. Courtesy Hubble Space Telescope Comet Team and NASA