Determination of Jupiter’s Pole Orientation from Juno Radio Science Data

Abstract

The extreme accuracy of Juno radio science data allows us to perform very precise orbit determination experiments. While previous works focused on the estimation of the gravitational field of Jupiter, in this article, we aim to accurately determine the planet’s orientation in space. For this purpose, we implement a rotational model of Jupiter, taking into account also its main deformations, as they affect the planet’s inertia components. Rotation parameters are estimated simultaneously with all other parameters (especially gravity and tides), in order to obtain a global and coherent solution. In our experiments, we find that Juno data manage to constrain Jupiter’s pole direction with an accuracy of around 10−7 radians for the whole duration of the mission, allowing us to improve its long-term ephemerides. Moreover, Juno data provide an upper bound on the maximum displacement between Jupiter’s pole and spin axis of less than 10 m, which allows us to investigate possible short-period nutation effects due to, for example, atmospheric and interior processes of the planet.