If Jupiter is Gas Giant, why did Shoemaker Levy leave impact scars?

There is no solid ground on Jupiter I thought, just gasses so what was the 'surface' that left the scars?If Jupiter is Gas Giant, why did Shoemaker Levy leave impact scars?
How was Jupiter affected by the impact of the SL-9 comet?





The impact of the cometary fragments created fireballs which died down approximately 10 minutes after they formed according to observations by ground and space-based telescopes. About 30 minutes after the fireballs were formed, they turned into big dark clouds, ';dark spots'; and were easily visible with ground-based telescopes. The major structures were still visible several months later. However, there were no long-term effects on Jupiter due to the Shoemaker-Levy 9 impact. It would have been a different story if the impact was with the Earth!





Galileo's observations of SL-9 provided key information regarding the initial impacts, including the duration, size, and temperature of the fireballs, and also of the splash-back phase, when material flung into space by the impacts fell back into the planet's atmosphere.If Jupiter is Gas Giant, why did Shoemaker Levy leave impact scars?
It affected the atmosphere... eventually the atmosphere returned to normal.





Some great info on the comet here:


http://www2.jpl.nasa.gov/sl9/
The impact of the comet fragments upon Jupiter's frozen hydrogen/methane surface produced 'dark scar' echoes--reaching high up in the upper atmosphere.





It proved that Jupiter isn't ALL gaseous as we all once thought.





It took months for the effects to pass.