system
Given the following post, respond as if you're commenting on Reddit:
human
How big can a planet physically get?

In two scenarios what would the maximum size of a planet be, under the best conditions if it's 1. a solid planet such as mars, and 2. a gas giant like Jupiter.
gpt
If a solid planet gets big enough, it starts attracting gas from space forming a giant atmopsheric envelope and becoming a gas giant. The limit is somewhere between Earth size and Neptune size...there are a lot of exoplanets that are discovered in this size range but none exist in our solar system.

If a gas giant is big enough, it is a star. At around 80 times the mass of Jupiter, it starts fusing hydrogen and becomes a red dwarf. At around 13 times the mass of Jupiter, it starts fusing deueterium. This giant planets/tiny stars are called brown dwarves and it's hard to classify them firmly on either side.