Ray Tracing for Titan’s Ionospheric Occultation of Saturn Radio Emissions: Implications for JUICE Mission

Titan has an ionosphere with complex variations caused by both solar radiation and its interaction with Saturn's magnetospheric plasma. Previous studies have examined Titan’s electron density using methods such as radio occultation and in situ measurements. However, additional observations are needed to better capture the spatial variability of the electron density—including its dependence on local time, latitude, and magnetic conditions—and to improve our understanding of the overall structure of Titan’s ionosphere.

In Yasuda et al. (2024), we developed a new method to estimate ionospheric electron densities using planetary auroral radio emissions. This technique was first applied to Galileo PWS data to study the ionospheres of Ganymede and Callisto, two Jovian moons with thin neutral atmospheres.

To extend this method using radio emissions from other planets or to adapt it for moons with dense atmospheres, we applied it to Cassini RPWS data to derive Titan's ionospheric electron density. We focused on the Titan 15 flyby and applied our method to obtain the electron density profile of Titan’s ionosphere. As a result, we confirmed that the method remains effective in this new configuration and successfully derived electron density profiles at several locations around Titan.

In addition, we used the polarization data from RPWS to identify the direction of the radio source. The polarization sense (right- or left-handed circular) clearly indicates whether the source was in the northern or southern hemisphere of Saturn. This allowed us to narrow down the possible radio source locations during the occultation. Our results demonstrate that polarization measurements are useful not only for identifying the origin of radio emissions but also for improving the accuracy of ionospheric measurements.

This approach has direct relevance to upcoming radio observations by the JUICE mission and is expected to support the characterization of the ionospheres of Jupiter’s icy moons in the 2030s. Cassini RPWS observations provide the closest available analog to JUICE RPWI data. Like RPWS, JUICE RPWI is equipped with three orthogonal electric antennas for detailed polarization measurements. This similarity makes RPWS data valuable for developing and validating analysis methods for JUICE. Our study suggests that applying this method to future JUICE data can yield new insights into the ionospheres of moons like Ganymede and Callisto, especially when combined with polarization measurements. We will present our analysis of the Titan 15 flyby and discuss how this approach can support future JUICE observations.