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The biggest moons of the biggest planets are some of the solar system's most remarkable worlds. One of the moons of Jupiter, for example, is covered with giant volcanoes, and geysers on the biggest moon of Neptune squirt dark ice particles and gas high into its thin atmosphere.
The most remarkable of all, though, has to be Titan, the largest moon of Saturn. And what makes it remarkable is not that it looks exotic, but that it looks familiar. Riverbeds flow across its surface, emptying into large lakes. Clouds waft through the sky, perhaps occasionally dumping rain. And giant fields of dunes undulate across its mid-section. In other words, it looks a lot like Earth.
And in some ways it may resemble the Earth of billions of years ago. It has a thick atmosphere that's rich in organic compounds -- the building blocks for life; more about that tomorrow.
There's one big difference between Earth and Titan, though: temperatures. Titan is so cold that water is frozen as hard as granite. So the liquid that forms the clouds, carves the rivers, and fills the lakes is probably ethane or methane. Even so, in many ways Titan is the most Earth-like world in the solar system -- a familiar landscape that makes it a remarkable world.
Saturn is in good view in the morning sky right now. It looks like a bright golden star. Tomorrow, it stands to the upper left of the Moon as they climb into view around 1 a.m. The star Spica rounds out the view, to the lower left of the Moon.
Script by Damond Benningfield, Copyright 2010