Titan, the largest moon of Saturn, is a deep freeze, with surface temperatures close to 300 degrees below zero Fahrenheit. But it would be even colder without one of the components of its atmosphere: methane. The gas traps heat from the Sun, making Titan dozens of degrees warmer.

Although it makes up only a small fraction of the dense atmosphere, methane plays a critical role in shaping Titan’s surface because it acts as water does here on Earth: It forms clouds, falls as rain, carves channels, and fills lakes.

Planetary scientists aren’t sure where the methane is coming from, though. Methane floats to the top of the atmosphere, where it’s destroyed by sunlight. The total supply in the atmosphere today wouldn’t last more than 10 million years. So more methane must somehow be entering the atmosphere.

Scientists have looked at several possibilities. One is that there may be deposits of methane-rich ice far below the surface. Some of the ice occasionally makes its way to the surface, adding fresh methane to the atmosphere. Scientists are combining observations from spacecraft and ground-based telescopes to try to pinpoint the source of this critical ingredient in Titan’s atmosphere; more about that tomorrow.

Bright golden Saturn stands high above the Moon as night falls this evening, with the star Spica close to Saturn’s lower right. Through a telescope, Titan looks like a tiny star quite close to the giant planet.

Script by Damond Benningfield, Copyright 2012