What keeps energetic gas molecules from escaping into space?

Question

Quizplus · Accepted Answer

Gravity is the force that holds the gas molecules in the atmosphere, preventing them from escaping into space. The gravitational force of Earth is strong enough to keep the gas molecules close to the surface, while weaker forces like interatomic and nuclear forces cannot compete with it. Solar radiation and the magnetic field may affect the behavior of the gas molecules in the atmosphere, but they do not act as a significant barrier against their escape into space.

What Keeps Energetic Gas Molecules from Escaping into Space