Gem hounds take note: Titan may hold some of the biggest and most unusual polished stones in the solar system. Radar data from the Cassini spacecraft show vast fields of smooth, rounded ice rocks--some more than 2 meters in diameter and nearly as transparent as rhinestones--on Xanadu, an Australia-sized plain south of the equator on Saturn's largest moon. Researchers have known about the stones ever since the European Huygens probe photographed Titan's landscape in January 2005 (above, left). But they didn't realize how many of them there were or that they were of such high quality. In a study published  in the June issue of Icarus, the team reports that the stones are similar to those found in streambeds on Earth (above, right), but instead of being formed by water, the Titan stones likely bounced along streambeds of liquid methane and ethane for billions of years, which polished them to a remarkable smoothness.
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