Jupiter’s Frequency-Dependent Love Number estimation through joint analysis of JUICE-3GM and Europa Clipper radio science measurements and one century of astrometry data

Abstract

The future JUICE and Europa Clipper missions will probe the Jovian system performing several flybys of the moons Europa, Ganymede, and Callisto. The precise radio tracking data will provide an accurate estimation of the gravity and ephemerides of the Galilean moons. This is especially true for Ganymede, after JUICE insertion in a low circular orbit around the moon for at least four months. The evolution of the orbits of the Galilean moons will allow for an estimation of the dissipation in Jupiter at the orbital frequency of each Galilean moon, represented/parameterized through the imaginary part of its degree-2 Love number.The imaginary part of the Jovian Love number  is a key parameter to evaluate the long-term orbital evolution of the Galilean moons and the Laplace resonance stability. Its secular effect on the orbit of the moons produces an acceleration both in the radial and tangential direction, and the longer the time span of observation, the better it can be estimated. However, the dissipations at the different satellite orbital frequencies are highly correlated due to the Laplace resonance, complicating their estimation. JUICE and Europa Clipper missions cover less than 5 years, but the accuracy in the determination of the moon’s orbit is good if not exquisite. This broad data set can be complemented by high quality astrometry measurements collected by ground observatories starting from 1891, past spacecraft missions (Voyager, Galileo) optical images and radar data. This approach has the potential to greatly improve the estimation accuracy for the dissipation parameters in Jupiter.Future work will include the addition of radio-tracking measurements from the spacecraft Galileo and Juno, which together with JUICE and Europa Clipper will offer a 30 year time span of radio-metric data.Unfortunately JUICE and Clipper, unlike Galileo and Juno, will fly never by Io, the moon which dominates the evolution of the Laplace resonance and the dissipation in the Jovian system. However Io can be observed from ground telescopes, and the available astrometric observations of the moon may allow a significant reduction of Io’s state solution uncertainties and correlations.In this study, we analyze the attainable uncertainties for the parameters characterizing the dissipation in Jupiter’s system and the ephemerides of the Galilean moons combining simulated range & range-rate radio tracking data from JUICE and Europa Clipper with astrometry data, showing the synergies and the possible improvements in the uncertainties and correlations of the joint analysis, together with a discussion of the problems associated to the fusion of data sets of very different type.