Presentation Information
[PPS01-P13]Preliminary analysis of Titan's ionospheric density structure using Saturn radio occultation
*Takeru Kato1, Rikuto Yasuda1, Yasumasa Kasaba1, Hiroaki Misawa1, Fuminori Tsuchiya1, Corentin Louis2, Baptiste Cecconi2, Tomoki Kimura3 (1.Tohoku University, 2.LIRA, Observatoire de Paris, CNRS, PSL Research University, 3.Tokyo University of Science)
Keywords:
Titan,Ionosphere,Occultation,Cassini
Titan is a Saturnian moon with a dense atmosphere. Its ionosphere is dominated by solar ultraviolet radiation and the intrusion of Saturn's magnetospheric plasma, exhibiting a complex structure rich in variability. Titan's atmosphere contains diverse hydrocarbons, and understanding their formation processes could also shed light on the origin of life on the primordial Earth. Since the formation of these organic compounds begins with ion-chemical reactions in the upper atmosphere, elucidating the ionosphere also provides insights into the composition and evolution of the neutral atmosphere.
Previous estimates of Titan's ionospheric electron density have been obtained through radio occultation methods using interplanetary communication signals, and direct in-situ observations using instruments like the Langmuir Probe and UHR frequencies. However, these methods have limitations in the analyzable altitude and local time (LT), resulting in particularly limited information for the low-altitude regions on both the day and night sides. This study applies the “Planetary Radio Occultation” method, proposed by Yasuda et al. (2024) for estimating the ionospheric density of Ganymede and Europa and subsequently applied to Titan's ionosphere, to Titan using a different observation point. This method uses the occultation of Saturn Kilometric Radiation (SKR) by the satellite’s ionosphere, enabling the derivation of ionospheric density during periods, Titan local times (LT), and Saturn-relative orbital phases (SLT) where estimation was previously impossible. SKR occultations promising for analysis have already been detected in approximately 30 of the 127 Titan flybys. While separating variations in the SKR itself is necessary, we are currently attempting to derive the structure of Titan's ionosphere from multiple data points within these occultations.
For this analysis, the radio source location was modeled using ExPRES (Exoplanetary and Planetary Radio Emission Simulator, Louis et al., 2019), a simulation tool for planetary auroral radio emissions developed by the Paris Observatory. We then use these simulated radio emissions to irradiate an ionospheric structure assumed to have a Gaussian distribution with diverse peak densities, heights, and widths.The occultation duration observable at each frequency by the probe was then evaluated using the Raytracing method we have developed. We compared these results with the actual occultation durations (intensity and polarization) of the SKR observed by the Cassini spacecraft's RPWS (Radio and Plasma Wave Science) instrument (2004–2017) to determine the most consistent ionospheric model.
This presentation reports on the analysis of occultations from the Titan-77 (T77) and Titan-119 (T119) flybys observed at different positions relative to Saturn, in addition to the Titan 15th flyby (T-15) analyzed in Yasuda et al. (submitted) and Yasuda et al. (JpGU). Furthermore, T119 has also been analyzed using conventional Radio Science methods and estimates based on direct in-situ observations; we will discuss comparisons with these results.
Previous estimates of Titan's ionospheric electron density have been obtained through radio occultation methods using interplanetary communication signals, and direct in-situ observations using instruments like the Langmuir Probe and UHR frequencies. However, these methods have limitations in the analyzable altitude and local time (LT), resulting in particularly limited information for the low-altitude regions on both the day and night sides. This study applies the “Planetary Radio Occultation” method, proposed by Yasuda et al. (2024) for estimating the ionospheric density of Ganymede and Europa and subsequently applied to Titan's ionosphere, to Titan using a different observation point. This method uses the occultation of Saturn Kilometric Radiation (SKR) by the satellite’s ionosphere, enabling the derivation of ionospheric density during periods, Titan local times (LT), and Saturn-relative orbital phases (SLT) where estimation was previously impossible. SKR occultations promising for analysis have already been detected in approximately 30 of the 127 Titan flybys. While separating variations in the SKR itself is necessary, we are currently attempting to derive the structure of Titan's ionosphere from multiple data points within these occultations.
For this analysis, the radio source location was modeled using ExPRES (Exoplanetary and Planetary Radio Emission Simulator, Louis et al., 2019), a simulation tool for planetary auroral radio emissions developed by the Paris Observatory. We then use these simulated radio emissions to irradiate an ionospheric structure assumed to have a Gaussian distribution with diverse peak densities, heights, and widths.The occultation duration observable at each frequency by the probe was then evaluated using the Raytracing method we have developed. We compared these results with the actual occultation durations (intensity and polarization) of the SKR observed by the Cassini spacecraft's RPWS (Radio and Plasma Wave Science) instrument (2004–2017) to determine the most consistent ionospheric model.
This presentation reports on the analysis of occultations from the Titan-77 (T77) and Titan-119 (T119) flybys observed at different positions relative to Saturn, in addition to the Titan 15th flyby (T-15) analyzed in Yasuda et al. (submitted) and Yasuda et al. (JpGU). Furthermore, T119 has also been analyzed using conventional Radio Science methods and estimates based on direct in-situ observations; we will discuss comparisons with these results.