Moon and Saturn
Titan, the largest moon of the planet Saturn, is one of a kind: It's the only moon in the solar system that has an atmosphere that's thicker than Earth's. And the atmosphere's main component is nitrogen -- the same gas that makes up most of our air.
But another compound in Titan's air is responsible for helping keep the air in place. Methane makes up just five percent of Titan's atmosphere, but it's a powerful greenhouse gas, so it warms the atmosphere by quite a bit. In fact, without this warming effect, Titan's air would get so cold that the nitrogen would condense and fall onto the surface, leaving the moon with almost no air at all.
Methane does other important things on Titan. It forms a cold rain, just like water raining on Earth. As the liquid methane hits the surface, it carves rivers, and it pools to form lakes. Over time, some of it evaporates back into the atmosphere, where it can once again form rain.
Methane is also responsible for Titan's orange color. Sunlight strikes some of the methane in the air and converts it to heavier molecules, which blanket the moon in an orange haze.
So while methane makes up only a fraction of Titan's atmosphere, it plays a major role in the satellite's daily life.
Saturn is in good view tonight. It looks like a bright star to the upper left of the Moon as they rise in mid-evening. Titan is visible through small telescopes. It looks like a tiny star quite near Saturn.
Script by Ken Croswell, Copyright 2008
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