Dynamical modelling of the Galilean moons for the JUICE mission

Abstract

Radio tracking and astrometric data obtained by the JUICE mission, using the PRIDE, 3GM and JANUS instruments, will allow the dynamics of the Galilean moons to be measured to unprecedented accuracy. As a result, the dynamical models used for creating ephemerides from these data will most likely require the inclusion of various heretofore neglected physical effects.To determine which effects will need to be included, we perform a sensitivity analysis of the influence on the dynamics of the system for a wide array of gravitational, tidal and rotational characteristics of the system. We estimate the dynamics of the Galilean moons with a given perturbation turned off, using ideal three-dimensional measurements of the satellites' positions generated with these perturbations turned on. In doing so, we assess the capabilities of the nominal dynamical model to absorb the influence of this perturbations. We analyze the dynamical behaviour over a period of five years, and limit our analysis to effects that may be observable from JUICE radio tracking and optical astrometry data. Our simulations comprise a short-period (5years) sensitivity analysis of the dynamics of the moons, and not a simulation of the tracking data inversion for JUICE.Our analysis indicates that the nominal dynamical model of the Galilean satellites can very efficiently absorb the influence of the current uncertainties in most of the physical parameters of the Jovian system, to a level where these uncertainties will not be influential for JUICE-derived ephemerides. An important exception is the influence of tidal dissipation: the k2/Q of Io will be clearly observable by JUICE tracking data, which will be strongly correlated with the weaker effect of Jupiter's k2/Q. The dissipation inside Europa may also be weakly constrained by JUICE tracking data. Without improvements in the Jovian gravity field from the Juno mission, the estimation of Jupiter zonal gravity field coefficients at degrees 2, 3 and 5 should be included in the ephemerides generation. The influence of the deviation from perfect tidal locking of the moons' rotation is at the limit of observability. Furthermore, we have verified that the present uncertainty in the a priori ephemeris of Jupiter will not influence the (Jupiter-centered) dynamics of the Galilean moons at an observable level.