The gravity harmonics of a fluid, rotating planet can be decomposed into static components arising from solid-body rotation and dynamic components arising from flows. In the absence of internal dynamics, the gravity field is axially and hemispherically symmetric and is dominated by even zonal gravity harmonics J that are approximately proportional to q, where q is the ratio between centrifugal acceleration and gravity at the planet's equator. Any asymmetry in the gravity field is attributed to differential rotation and deep atmospheric flows. The odd harmonics, J, J, J, J and higher, are a measure of the depth of the winds in the different zones of the atmosphere. Here we report measurements of Jupiter's gravity harmonics (both even and odd) through precise Doppler tracking of the Juno spacecraft in its polar orbit around Jupiter. We find a north-south asymmetry, which is a signature of atmospheric and interior flows. Analysis of the harmonics, described in two accompanying papers, provides the vertical profile of the winds and precise constraints for the depth of Jupiter's dynamical atmosphere.

The Juno spacecraft reached the mid‐point of its nominal mission in December 2018, after completing 17 perijove passes. Ten of these were dedicated to the determination of the gravity field of the planet, with the aim of constraining its interior structure. We provide an update on Jupiter's gravity field, its tidal response and spin axis motion over time. The analysis of the Doppler data collected during the perijove passes hints to a non‐static and/or non‐axially symmetric field, possibly related to several different physical mechanisms, such as normal modes or localized atmospheric or deeply‐rooted dynamics.

The moon Io is the dominant plasma source for the Jupiter magnetosphere. The plasma is distributed into a torus of material around Jupiter, called the Io plasma torus. The Juno spacecraft performed its first perijove on 27 August 2016. During this time the spacecraft's X and Ka‐band radio signals passed through the Io plasma torus. From the differential Doppler shift of the X and Ka‐band frequencies we are able to determine the Io plasma torus total electron content. From the total electron content, we determine that the electron densities are larger than predicted from Voyager‐based models by around 35 ± 14% in the cold torus and 38 ± 14% in the torus beyond 5.5 RJ. The ion temperatures were greater than predicted from the models by 44 ± 15% in the cold torus but consistent with models in the torus beyond 5.5 RJ. From the time of maximum total electron content, which is sensitive to the torus location, we also find the Io plasma torus equatorial plane appears to be tilted by about 1.5° more than the nominal centrifugal equator tilt based on the tilt of a dipole magnetic field approximation. Different tilts were found for the cold torus and torus beyond 5.5 RJ.

The atmosphere of the Jovian satellite Io is constantly being lost to the surrounding magnetosphere of Jupiter. The material is ionized and then distributed by Jupiter's magnetic field into a torus around Jupiter called the Io plasma torus. This plasma affects radio signals as they propagate from the Juno spacecraft to Earth during the spacecraft's perijove passes. During Perijoves 3, 6, and 8 we determine the total electron content in the Io plasma torus using two‐way tracking data from Juno. We find that the location of the torus is displaced from predictions that use the VIP4 offset tilted dipole approximation. The displacements are consistent with those found in ground‐based observations. The peak total electron content and scale height are found for two different regions of the torus, the cold inner torus and a warmer torus beyond 5.5 RJ. Properties of the cold torus vary appreciably with System III longitude, but properties of the torus beyond 5.5 RJ do not.

The combination of the Doppler data from the first two Juno science orbits provides an improved estimate of the gravity field of Jupiter, crucial for interior modeling of giant planets. The low‐degree spherical harmonic coefficients, especially J4 and J6, are determined with accuracies better than previously published by a factor of 5 or more. In addition, the independent estimates of the Jovian gravity field, obtained by the orbits separately, agree within uncertainties, pointing to a good stability of the solution. The degree 2 sectoral and tesseral coefficients, C2,1, S2,1, C2,2, and S2,2, were determined to be statistically zero as expected for a fluid planet in equilibrium.