RedEaredSlider writes "NASA's Cassini probe, in orbit around Saturn, may have discovered evidence for a liquid water ocean under the surface of Titan, Saturn's largest moon. The data comes from radar observations of the surface that measure Titan's rotation and tell how it is oriented relative to the plane of its orbit — its axial tilt. According to a paper to be published in an upcoming issue of Astronomy and Astrophysics (preprint PDF at arXiv.org), the new data showed that many of the planet's surface features were in the wrong place, sometimes off by as much as 30 kilometers (19 miles). Titan always presents the same face toward Saturn, just like the Moon does to Earth. But in those situations, one expects that the moon will be in the 'Cassini state,' which means that the axial tilt will have a certain value. In Titan's case, the axial tilt was measured at 0.3 degrees. That seemed too high if one assumed Titan was a solid body."