Exploring a New World: Titan as Revealed by Cassini's Radar
Saturn's moon Titan is larger than the planet Mercury and has a dense atmosphere like a planet. Until Cassini and its atmosphere-piercing radar got to Saturn little was known of Titan. Now with ~30% of the surface revealed Titan is seen to have a very young surface, with deserts of dunes, rivers, and hundreds of lakes and a few large seas of liquid methane/ethane.
We can infer that Titan is dynamically active, possibly with erupting volcanoes, blowing sediments, rainfall and rising and falling lake levels. In the debate about what is a planet, Titan would be considered a planet in all ways - except that it orbits another one.
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Wood, Chuck, "Exploring a New World: Titan as Revealed by Cassini's Radar" (2008). Space Studies Colloquium. 14.