Resolving the latitudinal short-scale gravity field of Jupiter using Slepian functions

Early gravity measurements performed by the Juno spacecraft determined Jupiter’s low16degree gravity coefficients, including the first estimate of the planet’s north-south asym17metric field. The retrieved information was used to infer that the strong zonal winds18 visible at the cloud tops must extend down a few thousand kilometers, where they are19 suppressed in the deep interior. The next frontier for the Juno gravity experiment in20cludes, among other goals, the determination of Jupiter’s small-scale gravity field with21 high accuracy, and its relation to atmospheric circulation at shorter length scales. The22 geometry of the Juno closest approaches to the planet poses a challenge to this task, as23 they span latitudes between +4 and +29 over the course of the nominal mission. Since24 Doppler measurements are the most sensitive to gravity anomalies when the spacecraft25 is close to the body, observations of Jupiter’s gravity field are mostly concentrated in the26 northern hemisphere, and traditional spherical harmonic functions are not orthonormal27 over a latitudinal subdomain. Here we define customized Slepian functions, which are28 orthogonal in a specific latitude range and are suitable to represent Jupiter’s local sur29face gravity at north latitudes. We show that with the new functions, the short-scale lat30itudinal variability of the gravity field is resolved with high accuracy between -15 and31 +45 latitude. Furthermore, preliminary results show that the estimated values for the32 Slepian coefficients from Juno data match the predictions obtained using a thermal wind33 model of Jupiter’s atmosphere for an optimized scale height.