system
Given the following post, respond as if you're commenting on Reddit:
human
Why do asteroid impacts leave 'scars' on gas giants?
gpt
You would be correct, if the gasses that Jupiter and other large planets were made of were simple and fairly well mixed. The asteroid would just plummet through them, leaving some smoke behind that would quickly dissipate, and that would be that.

However, the gas giants have striations not just along their latitude (the horizontal bands) but also in altitude (depth). So just like taking a step into a settled pond, a whoosh of stirred up different-colored stuff expands outwards from the impact.

Then, when the asteroid gets sufficiently hot and pressurized from the ramming effect of all that atmosphere (and long before it gets to the potential metallic hydrogen deep within), it explodes in a massive fireball. So now we're dropping grenades into the muddy pond analoge. It mostly expands upwards, away from the denser core of the planet, and all the way out into space. The hole that is left is rather like pulling your foot back up out of the muddy pond suddenly: a huge in and up rush of material that leaves the surface truly altered compared to neighboring regions. 

Then you have to wait for natural diffusion and winds to smear the scar out to remove it. These initial marks have nothing hard to contain them, so they can expand to the size of Earthly countries during the initial shock. It takes many days or even weeks for them to be mixed back to uniformity and/or drift back down in the case of heavier elements.