Analysis of Jupiter's Atmosphere Using Juno's Radio Occultations

The shallow layers of Jupiter’s atmosphere, the only region accessible to in-situ measurements, offer critical insights into the planet’s deeper structure. Radio occultation experiments are a powerful tool for investigating these layers, revealing detailed information about their thermal structure and composition. Beginning in July 2023, Juno’s extended mission carried out a series of radio occultations - the first since the Voyager era - to probe the neutral atmosphere of Jupiter down to approximately ±0.5 bar. By analyzing the refraction of radio signals as they pass through the atmosphere and comparing the results with ground-based observations, these experiments generate precise vertical profiles of key atmospheric parameters, particularly in the stratosphere
and upper troposphere.

Juno uses a coherent two-way radio link with multiple frequencies, requiring the application of ray-tracing techniques to model the propagation of uplink and downlink signals through the atmosphere. This approach enables the retrieval of pressure-temperature profiles, offering new insights into the thermal and dynamical structure of Jupiter’s atmosphere. Comparisons with contemporary ground-based measurements, as well as historical mid-infrared data from Voyager’s IRIS and Cassini’s CIRS instruments, highlight the value of these profiles in understanding atmospheric variability and circulation across different latitudes.

Since August 2024, Juno’s radio occultations have focused on Jupiter’s northern polar stratospheric vortex, a region (above ~65°N) known for its particularly low temperatures and distinct dynamical behavior. While the cold polar vortex has been detected in mid-infrared ground-based observations from VISIR and TEXES, Juno’s radio occultations offer the first opportunity to directly probe its thermal structure in detail. In this presentation, we share results from the first two years of Juno’s radio occultation campaign, highlighting pressure–temperature profiles across multiple latitudes and longitudes. These profiles help characterize the vertical extent, temperature gradients, and broader dynamical context of the polar vortex. In addition, we show how these thermal profiles can be used to quantify the jet velocity of the stratospheric vortex, providing new constraints on its intensity and latitudinal structure within Jupiter’s polar circulation.