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 Despite published predictions, astronomers had not expected to see the fireballs from the impacts and did not have any idea in advance how visible the other atmospheric effects of the impacts would be from Earth. Observers soon saw a huge dark spot after the first impact. The spot was visible even in very small telescopes, and was about (one Earth radius) across. This and subsequent dark spots were thought to have been caused by debris from the impacts, and were markedly asymmetric, forming crescent shapes in front of the direction of impact. Over the next six days, 21 distinct impacts