As scientists have predicted but have had a hard time proving, the surface of Titan, Saturn’s largest moon, appears to be dotted with lakes of liquid methane. The lakes are more intriguing evidence of the active phenomena at play on the only moon in the solar system with a dense atmosphere. The discovery, reported on Wednesday by an international team of researchers, was made by a radar survey of Titan’s high northern latitudes by the Cassini spacecraft, which has been orbiting Saturn and its retinue of satellites since July 2004.