New Constraints on Jupiter’s Ionosphere from Juno Radio Occultations

Radio occultation experiments constitute a powerful tool for probing the vertical structure of planetary atmospheres and ionospheres. Recently, the Juno mission has enabled a new generation of radio science investigations of Jupiter, allowing the characterization of its ionospheric electron density with a spatial resolution and latitudinal coverage not previously achievable. In this contribution, we present recent results from Juno radio occultation experiments conducted during the spacecraft’s extended mission, with a focus on their implications for the morphology and variability of Jupiter’s ionosphere.

As Juno passes behind Jupiter’s limb relative to Earth-based antennas, its radio signal propagates through the planet’s neutral atmosphere and ionized layers, undergoing refraction. This effect is observed as a deviation in the signal frequency received by NASA Deep Space Network antennas, compared to propagation through free space. The ionospheric contribution is inherently frequency-dependent and can be separated from non-dispersive effects associated with neutral refractivity and spacecraft motion by exploiting Juno’s dual-frequency radio links. In particular, this analysis is based on simultaneous X-band and Ka-band observations. Vertical electron density profiles are subsequently retrieved through an inversion procedure based on the ray-tracing technique, which accounts for Jupiter’s oblateness and assumes local axial symmetry of the ionosphere. A rigorous uncertainty assessment is performed using Monte Carlo simulations, allowing the propagation of measurement noise into confidence intervals for the retrieved profiles.

The data set considered here includes multiple occultation events acquired since mid-2023, at an approximate monthly cadence near perijove. Some of these events sample high-latitude regions in the northern hemisphere, providing new constraints on the ionospheric structure in proximity to the main auroral oval. The new results add to the occultations previously conducted by Pioneer, Voyager, and Galileo, providing us with a large data set. All these measurements reveal significant variability in peak electron density and vertical layering with latitude, longitude, and solar illumination conditions, and also point to a potential influence of magnetic field variations on ionospheric dynamics.

These observations provide new insights into Jupiter’s ionosphere and place important constraints on physical and empirical models. This work demonstrates the continued scientific return of Juno radio occultations and their relevance for the interpretation of future measurements from upcoming missions such as JUICE and Europa Clipper.