You're likely thinking of Titan, one of Saturn's moons. It's the only moon in our solar system known to have a dense atmosphere.

Here's what you need to know about Titan's atmosphere:

* It's thicker than Earth's: Titan's atmosphere is about 1.5 times denser than Earth's.

* It's mostly nitrogen: Just like Earth, Titan's atmosphere is primarily made of nitrogen (about 95%).

* It has methane and other gases: Titan also has methane, ethane, and other hydrocarbons in its atmosphere, contributing to its hazy orange color.

* It's cold and has low pressure: Titan's surface temperature is a frigid -179°C (-290°F), and the atmospheric pressure at the surface is about 1.5 times that of Earth's.

* It has clouds and rain: Titan experiences rain, but not of water. Instead, it rains liquid methane, which forms lakes and rivers on its surface.

So, while Titan isn't a planet, it's a fascinating moon with a rich and complex atmosphere.