The mass and size of the Moon and Triton (the satellite of Neptune) are approximately the same. Why can’t there

The mass and size of the Moon and Triton (the satellite of Neptune) are approximately the same. Why can’t there be an atmosphere on the Moon, but Triton does?

The mass and size of Triton and the Moon do not differ much, so the gravitational action of these objects is also the same. The atmosphere of a space object (planet, satellite, asteroid) is held by the force of gravity. But the Moon is closer to the Sun, therefore, the thermal velocities of the gas molecules that form the atmosphere are much greater at the distance of the Moon than at the distance of Triton. And these speeds are comparable to the cosmic speeds of the Moon. Therefore, even if the atmosphere of the moon is formed, the molecules will very soon fly away from their “mistress”.