 <unk> on the Galileo spacecraft observed fragments of Comet Shoemaker – Levy 9 between 16 and 22 July 1994 as they collided with Jupiter 's southern hemisphere at a speed of approximately 60 kilometres per second . This was the first direct observation of an extraterrestrial collision of solar system objects . While the impacts took place on the side of Jupiter hidden from Earth , Galileo , then at a distance of 1 @.@ 6 AU from the planet , was able to see the impacts as they occurred . Its instruments detected a fireball that reached a peak temperature of about 24 @,@ 000 K , compared to the typical Jovian <unk> temperature of about 130 K ( − 143 ° C ) , with the plume from the fireball reaching a height of over 3 @,@ 000 km . 
