5:15 PM - 7:15 PM
[PPS01-P08] Verification of Cassini 11+ Model against Non-CGF Orbit Data and Saturnian Internal Structure by Lowes Radius Analysis
Keywords:Saturn, Intrinsic magnetic field, Lowes radius, Internal structure
In this study, we first examined whether the latest intrinsic magnetic field model for Saturn, the Cassini 11+ model (Cao et al., 2020), maintains sufficient reproducibility for orbits other than the Cassini Grand Finale (CGF) orbits that were used for its optimization. Second, we attempted to estimate the dynamo radius within Saturn using the Lowes radius based on the observed Mauersberger-Lowes spectrum (Lowes, 1974). The Cassini 11+ model is an intrinsic magnetic field model for Saturn that is composed solely of zonal terms up to spherical harmonic degree 14.
Because the Cassini 11+ model was optimized using only the close approach orbit data from the final phase of the Cassini mission known as the Cassini Grand Finale (CGF), its applicability to vector magnetic field measurements observed along orbits other than the CGF orbits had not been verified. To address this issue, we performed a comparative analysis between the observed vector magnetic field data from orbits other than the CGF orbits and the corresponding model predictions in order to quantitatively assess the reproducibility of the Cassini 11+ model. The results showed that the Cassini 11+ model produces a fit that is comparable to or better than those by previous models (for example, Cassini 5) for non-CGF magnetic data and even when applied to vector magnetic data that were used in the optimization of neither the Cassini 11+ model nor previous models. It should be noted that this verification was carried out after updating the parameters of the magnetodisc model of Connerney et al. (1983) by using the Cassini magnetic data. The magnetodisc model represents the main external magnetic field component in Saturn's magnetosphere arising from the ring current.
With the high validity of the Cassini 11+ model confirmed by our tests, we further calculated Saturn's Mauersberger-Lowes spectrum based on the Cassini 11+ model and estimated the Lowes radius (Lowes, 1974) by three different methods. Specifically, we performed the estimation using only low degree terms (degree 6 and below), using only high degree terms (degree 7 and above), and using all terms (up to degree 14). We then compared the obtained radii with previous estimates of Saturn's internal structure. The comparison showed that the Lowes radius estimated from only the low degree terms was approximately one quarter of Saturn's radius, whereas the Lowes radii estimated using either high degree terms or all terms were both about 0.6 times Saturn's radius. The latter is consistent with the diffuse core radius suggested by recent studies on Saturn's ring seismology (Mankovich et al., 2021), while the former implies the presence of deep dynamo source stemming from movements of the liquid metallic hydrogen.
The results by this study should be cross-checked against the internal structures of Saturn derived from other disciplines such as gravity, thermal and chemical evolution of the planet and so on in the future. Nonetheless, the present results are expected to contribute to understanding of the dynamo region within Saturn based on magnetic field observations.
Because the Cassini 11+ model was optimized using only the close approach orbit data from the final phase of the Cassini mission known as the Cassini Grand Finale (CGF), its applicability to vector magnetic field measurements observed along orbits other than the CGF orbits had not been verified. To address this issue, we performed a comparative analysis between the observed vector magnetic field data from orbits other than the CGF orbits and the corresponding model predictions in order to quantitatively assess the reproducibility of the Cassini 11+ model. The results showed that the Cassini 11+ model produces a fit that is comparable to or better than those by previous models (for example, Cassini 5) for non-CGF magnetic data and even when applied to vector magnetic data that were used in the optimization of neither the Cassini 11+ model nor previous models. It should be noted that this verification was carried out after updating the parameters of the magnetodisc model of Connerney et al. (1983) by using the Cassini magnetic data. The magnetodisc model represents the main external magnetic field component in Saturn's magnetosphere arising from the ring current.
With the high validity of the Cassini 11+ model confirmed by our tests, we further calculated Saturn's Mauersberger-Lowes spectrum based on the Cassini 11+ model and estimated the Lowes radius (Lowes, 1974) by three different methods. Specifically, we performed the estimation using only low degree terms (degree 6 and below), using only high degree terms (degree 7 and above), and using all terms (up to degree 14). We then compared the obtained radii with previous estimates of Saturn's internal structure. The comparison showed that the Lowes radius estimated from only the low degree terms was approximately one quarter of Saturn's radius, whereas the Lowes radii estimated using either high degree terms or all terms were both about 0.6 times Saturn's radius. The latter is consistent with the diffuse core radius suggested by recent studies on Saturn's ring seismology (Mankovich et al., 2021), while the former implies the presence of deep dynamo source stemming from movements of the liquid metallic hydrogen.
The results by this study should be cross-checked against the internal structures of Saturn derived from other disciplines such as gravity, thermal and chemical evolution of the planet and so on in the future. Nonetheless, the present results are expected to contribute to understanding of the dynamo region within Saturn based on magnetic field observations.