Jupiter's Atmosphere Through Radio Occultations: From Current Measurements to JUICE

Radio occultation measurements provide a direct way to probe the vertical structure of Jupiter’s atmosphere. As a spacecraft radio signal passes through the planetary limb, it is refracted by the atmosphere, allowing profiles of refractivity, pressure, and temperature to be retrieved at high vertical resolution. The measurements are also used to probe Jupiter’s ionosphere, allowing electron density profiles to be retrieved in the upper atmospheric layers. For ESA’s Jupiter Icy Moons Explorer, JUICE, radio occultation experiments are planned to study the thermal structure and variability of Jupiter’s upper troposphere and lower stratosphere, the structure of the ionosphere, and their connection to broader questions of atmospheric circulation and dynamics.

 

The 3GM radio science experiment on JUICE will enable a new set of radio occultation measurements of Jupiter’s atmosphere using highly stable radio links. Around 100 occultation opportunities are expected during the mission, providing a broad sampling of latitudes and longitude. For the highest-resolution radio occultation experiments, we have developed an accurate varying spacecraft pointing technique during each observation. This approach is expected to allow the radio occultation experiments to penetrate to deep atmospheric levels, down to approximately 1.5 bar. In addition, the presence of an Ultra Stable Oscillator will enable one-way occultation measurements, which are especially valuable for retrieving high-resolution atmospheric profiles. 

 

At present, NASA's Juno mission provides the most extended radio occultation dataset of Jupiter's neutral atmosphere. Since July 2023, Juno has obtained the first new measurements of this kind since the Voyager era, sounding the atmosphere down to approximately 0.5 bar. These two-way coherent observations require ray tracing of both the uplink and downlink signals through Jupiter's oblate atmosphere, and have produced pressure-temperature profiles over a growing range of latitudes and longitudes. The analysis now includes measurements in the northern polar region, showing profiles that define the cold northern stratospheric vortex above 65 degrees north. The Juno results have already provided new constraints on Jupiter’s present day thermal structure, meridional variability, and polar dynamics.

 

In this presentation, we use the recent Juno radio occultation results as a foundation for preparing the atmospheric science of JUICE. Juno has already provided a new view of Jupiter’s upper troposphere and lower stratosphere, revealing vertical structure and variability that can guide the next stage of radio occultation studies. Building on these results, JUICE will extend the investigation with improved accuracy, higher vertical resolution, and the potential to sound deeper into the atmosphere than before. Together, these observations will provide a major step toward a more complete three-dimensional view of Jupiter’s thermal structure and atmospheric dynamics.