講演情報
[PPS01-P12]Titan's Ionospheric Density Structure Derived by Polarized Saturnian Radio Occultations during Cassini's Titan 15 Flyby
安田 陸人1、*三澤 浩昭1、Cecconi Baptiste2、Louis Corentin2、木村 智樹3、加藤 豪流1、笠羽 康正1、Gautier Thomas4,2、Grosset Lucas2、堺 正太朗5、土屋 史紀1 (1.東北大学大学院理学研究科惑星プラズマ・大気研究センター、2.パリ天文台LIRA、3.東京理科大学理学部第一部物理学科、4.LATMOS/IPSL, パリ-サクレ大学UVSQ, ソルボンヌ大学, CNRS、5.慶応大学環境情報学部)
キーワード：
土星、タイタン、電波掩蔽法、電離圏、氷衛星
Titan, Saturn's largest moon, possesses a dense nitrogen-rich atmosphere and a complex ionosphere shaped by photoionization and plasma precipitation. While Cassini's in situ measurements revealed key features such as solar zenith angle (SZA) dependence and variable electron densities, independent remote sensing techniques remain limited.
We present a new application of planetary radio occultation analysis using Saturn Kilometric Radiation (SKR) intensity and polarization data from Cassini's RPWS instrument. This study introduces a novel technique to independently estimate the radio source latitude by analyzing the cutoff frequency of each SKR polarization mode. By incorporating polarization analysis, we resolve the degeneracy between radio source location and ionospheric electron density structure, enabling accurate modeling of radio wave refraction during occultation.
Applied to the T15 flyby, the method yields peak electron densities of < 450 cm^-3 (altitudes < 1040 km) during ingress and >1200 cm^-3 (1290–1360 km) during egress. Comparison with 121 Langmuir Probe observations confirms a strong inverse correlation between electron density and SZA. We also identify a statistically significant negative correlation with solar EUV flux on the nightside (SZA > 100°), suggesting reduced ion precursor transport under high solar activity.
This technique offers a robust framework for remote sensing of dense ionospheres and is directly applicable to future JUICE/RPWI observations around icy moons.
We present a new application of planetary radio occultation analysis using Saturn Kilometric Radiation (SKR) intensity and polarization data from Cassini's RPWS instrument. This study introduces a novel technique to independently estimate the radio source latitude by analyzing the cutoff frequency of each SKR polarization mode. By incorporating polarization analysis, we resolve the degeneracy between radio source location and ionospheric electron density structure, enabling accurate modeling of radio wave refraction during occultation.
Applied to the T15 flyby, the method yields peak electron densities of < 450 cm^-3 (altitudes < 1040 km) during ingress and >1200 cm^-3 (1290–1360 km) during egress. Comparison with 121 Langmuir Probe observations confirms a strong inverse correlation between electron density and SZA. We also identify a statistically significant negative correlation with solar EUV flux on the nightside (SZA > 100°), suggesting reduced ion precursor transport under high solar activity.
This technique offers a robust framework for remote sensing of dense ionospheres and is directly applicable to future JUICE/RPWI observations around icy moons.