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 flow of material from Io's volcanoes into the Io plasma torus, out into the magnetosphere, and along field lines into Jupiter's upper atmosphere is not adequately understood. The lack of observations of spatial and temporal variations in the Io plasma torus impedes attempts to understand the system as a whole. Here we propose that radio occultations of the Io plasma torus by the Juno spacecraft can measure plasma densities in the Io plasma torus. We find that the line‐of‐sight column density of plasma in each of the three regions of the Io plasma torus (cold torus, ribbon, and warm torus) can be measured with uncertainties of 10%. We also find that scale heights describing the spatial variation in plasma density in each of these three regions can be measured with similar uncertainties. Such observations will be sufficiently accurate to support system‐scale studies of the flow of plasma through the magnetosphere of Jupiter.

In Jupiter’s magnetosphere, the structure of the plasma sheet depends on the magnetic field geometry and the centrifugal forces on the plasma. We present a simple formulation for the centrifugal equator, the farthest point along a magnetic flux tube from the planetary spin axis, for Jupiter’s torus to plasma sheet region (5–30 jovian radii). The formulation is based on a dipole magnetic field and azimuthally symmetric current sheet, both tilted by 9.5° toward System III west longitude of 201°. We find a good fit to such a model with a hyperbolic tangent function varying sinusoidally with longitude. The latitudinal angle of the derived centrifugal equator relative to the jovigraphic equator changes from the dipolar value (2/3 of the dipole tilt) around 5 jovian radii to close to the full dipole tilt at 25 jovian radii.

The innermost Galilean satellite, Io, is the source of most of the material in Jupiter's magnetosphere. This material, made mostly of sulfur and oxygen atoms, gets ionized and trapped by Jupiter's magnetic field (Thomas et al., 2004). The ionized material is transported radially through the magnetosphere. The plasma is then lost via charge exchange with neutrals or transported to the outer magnetosphere. The highest density of the plasma lies between 5 and 10 R J in what is called the Io plasma torus (IPT). The plasma trapped in the IPT is distributed into three distinct regions: the cold torus, ribbon, and warm torus (