Title: The Revival of Radio Occultations: Investigating the Atmospheres of Jupiter and Saturn
Speaker: Dr. Maria Smirnova (Weizmann Institute of Science)
Abstract:
Radio occultation (RO) is a uniquely powerful technique for probing giant planet atmospheres. As a spacecraft radio signal passes behind the planetary limb, it is refracted by the atmosphere, and the measured changes in the signal can be inverted to retrieve high-vertical-resolution profiles of refractivity, density, pressure, and temperature from the upper troposphere into the stratosphere. At rapidly rotating and strongly oblate planets, these measurements require dedicated ray-tracing inversions that account for planetary shape, gravity, winds, and the full radio-path geometry.
At Jupiter, NASA’s Juno mission has produced the first new atmospheric radio occultations since Voyager. Since 2023, we have retrieved more than 50 temperature-pressure profiles spanning low, mid, and polar latitudes, with measurements reaching depths of about 0.6 bar. This growing dataset is now allowing us to compare Jupiter’s thermal structure across various dynamical regimes. Recent observations probe the cold northern polar stratospheric vortex and regions close to the polar cyclones, while lower-latitude profiles reveal variations in atmospheric stability and vertical structure. Together, these measurements provide new constraints on coupling between the stratosphere and upper troposphere, as well as on vertical mixing, waves, and large-scale dynamics. Comparison with TEXES and Cassini’s CIRS observations places the Juno profiles within a broader picture of Jupiter’s spatial and temporal thermal variability.
At Saturn, we are revisiting the extensive but still largely underexplored Cassini radio occultation archive, comprising more than 75 atmospheric RO measurements collected over the mission’s 13-year tour. These observations span a wide range of latitudes and the transition from northern winter toward northern summer, providing a unique record of Saturn’s atmosphere over more than a decade of seasonal change. By processing these observations within a common framework, we are constructing a mission-long view of Saturn’s upper troposphere and lower stratosphere. The dataset allows us to investigate temperature variability near the 1-bar level, changes in vertical thermal structure with latitude and season, and dynamical variability in the stratosphere, including Saturn’s stratospheric oscillation.
Together, Juno and Cassini show that radio occultations are more than individual vertical profiles: they provide anchors for the thermal structure of giant planet atmospheres. Their high vertical resolution allows us to probe layers where infrared retrievals can be limited by vertical smoothing and temperature–composition degeneracies. Accompanied by other ground- and space-based observations, they provide an independent reference for tracing atmospheric structure across altitude, latitude, season, and dynamical regime. This revival of giant planet radio occultations is opening a new window on atmospheric dynamics, seasonal evolution, and vertical coupling, with ESA’s JUICE extending this record in the future.