system
Given the following post, respond as if you're commenting on Reddit:
human
What would happen if two gas giants (say Jupiter and Saturn) would collide?

Lets say you place Jupiter at one end of a run way, and on the otehr end you place Saturn. You trigger something to where both planets are in line and will directly hit each other. Since they are the most massive planets, would any gas be able to escape due to gravitation? How would a gas giant collision look like? Would they just mesh up and form one giant gas planet, or would the gas just escape into space?
gpt
On planetary scales, aggregation does not matter. Whether the planet is made of solids, liquids, or gas, makes very little difference. Gravity trumps everything else.

Collisions of such large planetary bodies would release a tremendous amount of heat, partly due to kinetic energy (the speed of one planet bumping into the other), partly from gravity. The merged body would be quite hot initially.

Depending on the collision speed, angle, whether it's frontal collision or just "grazing", etc., the planets may merge more or less into a single ~~bigger~~ heavier planet, or would shatter and spew out pieces of material all over the place. The pieces would tend to either fall back down, or remain in orbit around the merged body and coalesce into one or several moons.

It is not impossible that some fragments would end up ejected at high speeds and keep moving forever away from the collision, although that's probably not very typical.

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EDIT: Do not imagine that planets are either solid, or liquid, or gas. Think of them as giant loose piles of little billiard balls, kept together only by gravity, and that will give you a much better understanding of what happens during a collision.