Titan below Saturn's magnetodisc: Results from 3D hybrid simulations and Cassini MAG observations

In the idealized picture of Titan's plasma interaction deduced from Voyager 1 data, the ambient magnetic field is assumed to be perpendicular to the moon's orbital plane. However, Cassini observations suggest that the situation is significantly more complex: Titan is typically located below (above) its parent planet's warped and highly dynamic magnetodisc in southern (northern) summer. The magnetic field near Titan's orbit does not only possess a component towards Saturn, but Cassini MAG data obtained in southern summer also suggest the presence of a significant field component along the corotational flow direction. We present observations from the Cassini MAG instrument during the southern summer conditions of the prime mission, illustrating the high variability of the magnetic field conditions along Titan's orbit. Furthermore, by applying a three-dimensional hybrid model (kinetic ions, fluid electrons), we investigate systematically how Titan's plasma interaction is affected by a deviation of the ambient magnetic field from orthogonality. The model also takes into account the vertical gradient of the plasma composition in Saturn's magnetosphere: The heavy ion species are confined to the magnetic equator, whereas above and below, the impinging magnetospheric plasma mainly consists of light hydrogen ions. Our simulations show that introducing a flow-aligned magnetic field component goes along with an asymmetrization of Titan's magnetotail, in addition to the asymmetry that already arises from the large gyroradii of the ion species involved in the interaction. In the vicinity of Titan, the field lines become strongly twisted, permitting the wakeside magnetic lobe structure to even penetrate into the satellite's geometric plasma shadow. However, despite the increased complexity of Titan's magnetic environment, the overall characteristics of the pick-up ion tail remain practically the same as in the case of ideal magnetic field orientation.