Bryan W. Stiles Randolph L. Kirk Michael D. Allison Paolo Persi del Marmo Luciano Iess Jonathan I. Lunine Steven J. Ostro Scott Hensley Ralph D. Lorenz 2008 <p><span>Cassini radar observations of Saturn's moon Titan over several years show that its rotational period is changing and is different from its orbital period. The present-day rotation period difference from synchronous spin leads to a shift of ∼0.36° per year in apparent longitude and is consistent with seasonal exchange of angular momentum between the surface and Titan's dense superrotating atmosphere, but only if Titan's crust is decoupled from the core by an internal water ocean like that on Europa.</span></p> application/pdf 10.1126/science.1151639 en American Association for the Advancement of Science (AAAS) Titan's rotation reveals an internal ocean and changing zonal winds article