Comet Shoemaker–Levy 9 A of the nucleus entered Jupiter's southern hemisphere at a speed of about . Instruments on "Galileo" detected a fireball that reached a peak temperature of about , compared to the typical Jovian cloudtop temperature of about , before expanding and cooling rapidly to about after 40 seconds. The plume from the fireball quickly reached a height of over . A few minutes after the impact fireball was detected, "Galileo" measured renewed heating, probably due to ejected material falling back onto the planet. Earth-based observers detected the fireball rising over the limb of the planet shortly after the initial impact.
Comet Shoemaker–Levy 9 thus a serendipitous discovery, but one that quickly overshadowed the results from their main observing program. Comet Shoemaker–Levy 9 was the ninth periodic comet (a comet whose orbital period is 200 years or less) discovered by the Shoemakers and Levy, hence its name. It was their eleventh comet discovery overall including their discovery of two non-periodic comets, which use a different nomenclature. The discovery was announced in IAU Circular 5725 on March 27, 1993. The discovery image gave the first hint that comet Shoemaker–Levy 9 was an unusual comet, as it appeared to show multiple nuclei in an elongated region