TY - JOUR
T1 - Interpreting the librations of a synchronous satellite – How their phase assesses Mimas’ global ocean
AU - Noyelles, Benoît
N1 - Funding Information:
This study took benefit from the financial support of the contract Prodex CR90253 from the Belgian Science Policy Office (BELSPO), and is part of the activities of the ISSI Team Constraining the dynamical timescale and internal processes of the Saturn System from astrometry. I am indebted to Rose–Marie Baland, Marie Yseboodt, and two anonymous reviewers, for their careful readings and valuable suggestions.
Publisher Copyright:
© 2016
PY - 2017/1/15
Y1 - 2017/1/15
N2 - Most of the main planetary satellites of our Solar System are expected to be in synchronous rotation, the departures from the strict synchronicity being a signature of the interior. Librations have been measured for the Moon, Phobos, and some satellites of Saturn. I here revisit the theory of the longitudinal librations in considering that part of the interior is not hydrostatic, i.e. has not been shaped by the rotational and tidal deformations, but is fossil. This consideration affects the rotational behavior. For that, I derive the tensor of inertia of the satellite in splitting these two parts, before proposing an analytical solution that I validate with numerical simulations. I apply this new theory on Mimas and Epimetheus, for which librations have been measured from Cassini data. I show that the large measured libration amplitude of these bodies can be explained by an excess of triaxiality that would not result from the hydrostatic theory. This theory cannot explain the phase shift which has been measured in the diurnal librations of Mimas. This speaks against a solid structure for Mimas, i.e. Mimas could have a global internal ocean.
AB - Most of the main planetary satellites of our Solar System are expected to be in synchronous rotation, the departures from the strict synchronicity being a signature of the interior. Librations have been measured for the Moon, Phobos, and some satellites of Saturn. I here revisit the theory of the longitudinal librations in considering that part of the interior is not hydrostatic, i.e. has not been shaped by the rotational and tidal deformations, but is fossil. This consideration affects the rotational behavior. For that, I derive the tensor of inertia of the satellite in splitting these two parts, before proposing an analytical solution that I validate with numerical simulations. I apply this new theory on Mimas and Epimetheus, for which librations have been measured from Cassini data. I show that the large measured libration amplitude of these bodies can be explained by an excess of triaxiality that would not result from the hydrostatic theory. This theory cannot explain the phase shift which has been measured in the diurnal librations of Mimas. This speaks against a solid structure for Mimas, i.e. Mimas could have a global internal ocean.
KW - Resonances
KW - Satellites
KW - Shapes – Celestial mechanics – Saturn
KW - Spin-orbit – Rotational dynamics – Satellites
UR - http://www.scopus.com/inward/record.url?scp=84994669200&partnerID=8YFLogxK
U2 - 10.1016/j.icarus.2016.10.001
DO - 10.1016/j.icarus.2016.10.001
M3 - Article
AN - SCOPUS:84994669200
SN - 0019-1035
VL - 282
SP - 276
EP - 289
JO - Icarus
JF - Icarus
ER -