Which Planets Have an Atmosphere? Effect of Mass

If two planets are the same in every other way, the one with a stronger gravitational pull is more likely to have an atmosphere. The stronger a planet’s gravity is, the higher its escape velocity: the faster the gas molecules have to be moving to escape the planet’s gravity and fly out into space. This is one reason Earth has an atmosphere while the Moon does not: Earth and the Moon are located the same distance from the Sun and receive the same amount of energy, but the Moon is too small to hold onto an atmosphere.