Ah, no. The Earth's gravitational field provides exactly that. It pulls gas molecules to the planet. Yes, some escape but the majority are kept tight to Earth.

Consider the Sun. it is a big ball of gas. Why then doesn't it all evaporate and the Sun become smaller and go out? Because the gravitational field creates, effectively, an invisible 'force' container.

Ah, no. The Earth's gravitational field provides exactly that. It pulls gas molecules to the planet. Yes, some escape but the majority are kept tight to Earth.

Consider the Sun. it is a big ball of gas. Why then doesn't it all evaporate and the Sun become smaller and go out? Because the gravitational field creates, effectively an invisible 'force' container.