Chaotic rotation of Hyperion?

Saturn's satellite Hyperion has been predicted to be in a chaotic rotation state as a result of its irregular shape and tidal interactions1. However, an analysis of Voyager 2 images by Thomas et al.2 contradicted this prediction. These authors analysed 14 images obtained over 61 days and interpreted them to be consistent with a coherent (non-chaotic) rotation period of 13.1 days. The interpretation of the Voyager data has, however, been criticized by Peale and Wisdom3, who argued that the low sampling frequency does not allow chaotic or non-chaotic rotation to be distinguished. We report here new observations which were obtained with a higher sampling frequency. These data conclusively show that the 13.1-day period found by Thomas et al. was not due to coherent rotation.