caa a22 4500 445863382 CHVBK 20180317145450.0 cr unu---uuuuu 170323e20110501xx s 000 0 eng 10.1007/s10569-011-9337-3 doi (NATIONALLICENCE)springer-10.1007/s10569-011-9337-3 Rotational modeling of Hyperion [Elektronische Daten] [Rebecca Harbison, Peter Thomas, Philip Nicholson] Saturn's moon, Hyperion, is subject to strongly-varying solid body torques from its primary and lacks a stable spin state resonant with its orbital frequency. In fact, its rotation is chaotic, with a Lyapunov timescale on the order of 100days. In 2005, Cassini made three close passes of Hyperion at intervals of 40 and 67days, when the moon was imaged extensively and the spin state could be measured. Curiously, the spin axis was observed at the same location within the body, within errors, during all three fly-bys—~ 30° from the long axis of the moon and rotating between 4.2 and 4.5 times faster than the synchronous rate. Our dynamical modeling predicts that the rotation axis should be precessing within the body, with a period of ~ 16days. If the spin axis retains its orientation during all three fly-bys, then this puts a strong constraint on the in-body precessional period, and thus the moments of inertia. However, the location of the principal axes in our model are derived from the shape model of Hyperion, assuming a uniform composition. This may not be a valid assumption, as Hyperion has significant void space, as shown by its density of 544± 50 kg m−3 (Thomas etal. in Nature 448:50, 2007). This paper will examine both a rotation model with principal axes fixed by the shape model, and one with offsets from the shape model. We favor the latter interpretation, which produces a best-fit with principal axes offset of ~ 30° from the shape model, placing the A axis at the spin axis in 2005, but returns a lower reduced χ 2 than the best-fit fixed-axes model. Springer Science+Business Media B.V., 2011 Chaotic motions nationallicence Extended body dynamics nationallicence Natural satellites nationallicence Satellite rotation nationallicence Hyperion principal axes nationallicence Harbison Rebecca Department of Astronomy, Cornell University, 610 Space Sciences Building, 14853, Ithaca, NY, USA aut Thomas Peter Department of Astronomy, Cornell University, 610 Space Sciences Building, 14853, Ithaca, NY, USA aut Nicholson Philip Department of Astronomy, Cornell University, 610 Space Sciences Building, 14853, Ithaca, NY, USA aut Celestial Mechanics and Dynamical Astronomy Springer Netherlands 110/1(2011-05-01), 1-16 0923-2958 110:1<1 2011 110 10569 https://doi.org/10.1007/s10569-011-9337-3 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s10569-011-9337-3 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Harbison Rebecca Department of Astronomy, Cornell University, 610 Space Sciences Building, 14853, Ithaca, NY, USA aut NATIONALLICENCE 700 1- Thomas Peter Department of Astronomy, Cornell University, 610 Space Sciences Building, 14853, Ithaca, NY, USA aut NATIONALLICENCE 700 1- Nicholson Philip Department of Astronomy, Cornell University, 610 Space Sciences Building, 14853, Ithaca, NY, USA aut NATIONALLICENCE 773 0- Celestial Mechanics and Dynamical Astronomy Springer Netherlands 110/1(2011-05-01), 1-16 0923-2958 110:1<1 2011 110 10569 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer