system
Given the following post, respond as if you're commenting on Reddit:
human
What's the thickest atmosphere that Earth could conceivably support? Would each kilogram of atmosphere have enough gravity to hold another kilogram of atmosphere or is there some upper bound?
gpt
There is an upper bound - stellar ignition when the pressure is high enough to start fusion and instead of a planet you have a star.

This close to our parent star, though... the solar wind stops us from accumulating any more atmosphere and what we do have is due to the shielding effect of our magnetic field.