Saturn is the second largest planet in the solar system, a host of 62 satellites and prominent rings. The saturnian system exhibits a variety of distinctive physical and dynamical properties, alluding to a complex history of evolution. The satellites vary remarkably in size, mass, and thus internal structure. While most reside in near-circular orbits, their present-day configuration embodies numerous intricate mutual interactions as well as those with the rings and primary. Many satellites are known to have been tidally locked into near-synchronous rotation with their long axes always directed towards Saturn. Variability arises, however, in the form of librations with respect to the mean rotation state as a result of torques and perturbations raised by other objects. The observation of the rotational variability sheds light on a body's interior mass distribution. In particular, together with the gravitational field model, it yields direct and sufficient constraint on the body's moments of inertia.

We analyze the optical observations acquired by the Imaging Sub-system onboard the Cassini spacecraft during its 20 year exploration of the saturnian system. Thanks to the availability of high resolution data and their extensive temporal coverage, we aim to improve the determination of the satellites' shapes and rotation states adapting an in-house developed tool for inertial frame bundle block adjustment, which has been applied to the martian moon, Phobos, and asteroid, 4 Vesta (Burmeister 2017). We study the implications of the updated rotational models on the interior structures and conditions of the satellites in the broad context of plausible formation and evolution scenarios of the saturnian system.

The work is supported by DFG under project “The Satellites of Saturn after the Cassini Mission: Updated Geodetic Parameters and Interpretations for Interior Structures and Dynamics”, number 422047434.

Contact:  Dr. Xuanyu Hu