The only moon in our solar system with a substantial atmosphere is Titan, which orbits Saturn.

Here's why:

* Titan's atmosphere is denser than Earth's. It's composed mainly of nitrogen, with methane and other hydrocarbons.

* It has weather patterns and lakes of liquid methane. The atmosphere supports clouds, rain, and even rivers and seas of liquid methane.

While other moons have very thin atmospheres (like Mars' moons Phobos and Deimos), Titan's is the only one that qualifies as substantial.