Only one moon in our solar system is known to have a substantial atmosphere: Titan, a moon of Saturn.

While other moons have very thin atmospheres, or exospheres, Titan's atmosphere is thick enough to be considered a true atmosphere. It's composed mainly of nitrogen, with methane and other hydrocarbons.

Here's a breakdown:

* Titan: Dense atmosphere, mostly nitrogen.

* Other moons: Thin exospheres, often composed of gases escaping from the surface due to solar radiation or volcanic activity. These are too thin to be considered true atmospheres.