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New constraints on Saturn's interior from Cassini astrometric data | | Valéry Lainey
; Robert A. Jacobson
; Radwan Tajeddine
; Nicholas J. Cooper
; Carl Murray
; Vincent Robert
; Gabriel Tobie
; Tristan Guillot
; Stéphane Mathis
; Françoise Remus
; Josselin Desmars
; Jean-Eudes Arlot
; Jean-Pierre De Cuyper
; Véronique Dehant
; Dan Pascu
; William Thuillot
; Christophe Le Poncin-Lafitte
; Jean-Paul Zahn
; | | Date: |
20 Oct 2015 | | Abstract: | Using astrometric observations spanning more than a century and including a
large set of Cassini data, we determine Saturn’s tidal parameters through their
current effects on the orbits of the eight main and four coorbital moons. We
have used the latter to make the first determination of Saturn’s Love number,
$k_2=0.390 pm 0.024$, a value larger than the commonly used theoretical value
of 0.341 (Gavrilov & Zharkov, 1977), but compatible with more recent models
(Helled & Guillot, 2013) for which $k_2$ ranges from 0.355 to 0.382. Depending
on the assumed spin for Saturn’s interior, the new constraint can lead to a
reduction of up to 80% in the number of potential models, offering great
opportunities to probe the planet’s interior. In addition, significant tidal
dissipation within Saturn is confirmed (Lainey et al., 2012) corresponding to a
high present-day tidal ratio $k_2/Q=(1.59 pm 0.74) imes 10^{-4}$ and
implying fast orbital expansions of the moons. This high dissipation, with no
obvious variations for tidal frequencies corresponding to those of Enceladus
and Dione, may be explained by viscous friction in a solid core, implying a
core viscosity typically ranging between $10^{14}$ and $10^{16}$ Pa.s (Remus et
al., 2012). However, a dissipation increase by one order of magnitude at Rhea’s
frequency could suggest the existence of an additional, frequency-dependent,
dissipation process, possibly from turbulent friction acting on tidal waves in
the fluid envelope of Saturn (Ogilvie & Li, 2004). Alternatively, a few of
Saturn’s moons might themselves experience large tidal dissipation. | | Source: | arXiv, 1510.5870 | | Services: | Forum | Review | PDF | Favorites | |
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