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Moon and Companions
[SFX: Huygens entry]
That’s the sound of the atmosphere of Titan, the largest moon of Saturn, whizzing past the Huygens probe as it parachuted toward the surface in 2005. The probe and its mothership, Cassini, found that like Earth, Titan’s atmosphere consists of a series of layers. But because Titan’s gravity is weaker than Earth’s, its atmosphere extends much farther into space.
Titan is the only moon in the solar system with an appreciable atmosphere. The air is denser than Earth’s, and much colder. It consists mainly of nitrogen — the main ingredient in the air here on Earth — with a small amount of methane and other compounds.
The outermost parts of the atmosphere are mere wisps of gas. Below those wisps there’s an orange haze that’s rich in organic compounds — the equivalent of smog. And below that, there are layers of clear air sandwiched around a layer that supports clouds. These clouds appear to rain methane onto Titan’s surface, where it carves channels and fills lakes.
One of the puzzles about Titan’s atmosphere is where the methane comes from. It’s a lightweight gas that floats to the top of the atmosphere, where it’s destroyed by sunlight. That means something is pumping more methane into the atmosphere; we’ll have more about that tomorrow.
In the meantime, look for Saturn to the lower left of the Moon this evening. It looks like a bright golden star, with the true star Spica nearby, a bit closer to the Moon.
Script by Damond Benningfield, Copyright 2012
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