A massive river snaking over the surface of Titan, one of Saturn's moons, looks like the Nile River and means the moon may be geologically active. Titan -- believed to be the body most similar to Earth in the solar system -- is too cold for water, but hydrocarbons such as ethane flow in its lakes and streams. "Usually when we look at another planet, we're cautioned not to bring our Earth experience too much to bear, because we might fool ourselves," said NASA Jet Propulsion Laboratory researcher Thomas Farr. "But here we look at a completely alien world and it looks just like the Earth. It's hard to believe."