Abstract
Abstract. Titan's interaction with the corotating Saturnian magnetospheric plasma is studied in terms of a three-dimensional electromagnetic hybrid model. This approach treats the electrons as a massless, charge-neutralizing fluid, whereas the ions are represented by macroparticles. The model considers two magnetospheric and three ionospheric ion species. In contrast to any foregoing simulation study, the magnetospheric upstream conditions are not assumed to be stationary, but time variations have been imposed on the electromagnetic fields. The model includes simple periodic distortions of the fields near Titan, the purpose being to illustrate the basic physical mechanisms of ion pick-up in a non-stationary electromagnetic environment. In order to allow a straightforward access to the influence of the electromagnetic field orientation on the pick-up, no variations have been imposed on the density of the impinging magnetospheric plasma. Under stationary upstream conditions, Titan's exospheric tail exhibits a strong asymmetry with respect to the direction of the convective electric field. The simulations show that this characteristic asymmetry cannot develop, if the ambient electromagnetic fields are highly distorted. However, the central tail region directly behind the satellite remains nearly unaffected by the distorted magnetospheric upstream conditions. The central tail where the slow ionospheric species are predominant is able to shield itself against any kind of distortion in the ambient magnetospheric field conditions. The shorter the time period of the distortions, the more efficient is this shielding effect. The dependency of the pick-up on the characteristic time scales of the distortions is discussed in detail for the investigated model cases. Besides, the reaction of Titan's exospheric tail structure on sudden, non-continuous changes of the magnetospheric plasma conditions is analyzed, providing an illustration of some effects that may occur when Titan crosses Saturn's magnetopause.
Highlights
During the ongoing Cassini mission to the Saturnian system, more than 30 flybys of the giant planet’s largest moon, Titan, have already been accomplished
The plasma and magnetic field data collected by the Cassini instruments have greatly improved our understanding of the interaction of Titan’s dense, nitrogenrich atmosphere and ionosphere with the corotating Saturnian magnetospheric plasma flow
The Cassini mission provides a variety of new scientific information on the interaction between Titan’s ionosphere and the impinging magnetospheric plasma of Saturn
Summary
During the ongoing Cassini mission to the Saturnian system, more than 30 flybys of the giant planet’s largest moon, Titan, have already been accomplished. The authors refer to this as the magnetospheric mass spectrometer effect This five-species model has been successfully applied to reproduce and explain some features of Titan’s magnetic field signature during the ninth Cassini encounter (T9) on 26 December 2005 (Simon et al, 2007). Luhmann (1996) who studied the structure of Titan’s exospheric tail in the framework of a test particle model suggested that short-scale magnetic fluctuations may have significant impact on the satellite’s asymmetric tail structure, especially on the spatial dispersion of species of different masses (ionospheric mass spectrometer effect) This aspect has so far not been addressed by any of the global, three-dimensional simulation approaches. The final section gives a short summary of our major results
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