Abstract
Abstract. The Cassini mission has provided much information about the Titan environment, with numerous low altitude encounters with the moon being always inside the magnetosphere. The only encounter taking place outside the magnetopause, in the magnetosheath, occurred the 13 June 2007 (T32 flyby). This paper is dedicated to the analysis of the Radio and Plasma Wave investigation data during this specific encounter, in particular with the Langmuir probe, providing a detailed picture of the cold plasma environment and of Titan's ionosphere with these unique plasma conditions. The various pressure terms were also calculated during the flyby. The comparison with the T30 flyby, whose geometry was very similar to the T32 encounter but where Titan was immersed in the kronian magnetosphere, reveals that the evolution of the incident plasma has a significant influence on the structure of the ionosphere, with in particular a change of the exo-ionospheric shape. The electrical conductivities are given along the trajectory of the spacecraft and the discovery of a polar plasma cavity is reported.
Highlights
The Cassini mission has substantially progressed our knowledge of the Saturnian environment since the 1 July 2004, in particular regarding the largest satellite, Titan
We present electrical conductivities calculated in the extended ionosphere, and we report the discovery of a polar plasma cavity whose formation process is discussed
We focused, in the inbound leg, on the dense region, where the upper hybrid emissions may be used as a reference for the electron density
Summary
The Cassini mission has substantially progressed our knowledge of the Saturnian environment since the 1 July 2004, in particular regarding the largest satellite, Titan. Titan was located in the magnetosheath region, embedded in a shocked solar wind plasma, very close to the magnetopause. During this pass, the MAG experiment (magnetic field data) exhibited the presence of “fossil” field lines (Bertucci et al, 2008), with a magnetospheric-like configuration in the atmosphere, very different from the magnetosheath magnetic field configuration observed at higher altitudes. We analyze in detail the Cassini RPWS (Langmuir probe in particular) observations (Gurnett et al, 2004) during the T32 flyby, in order to study the unknown response of the ionosphere to a magnetosheath plasma environment. We present electrical conductivities calculated in the extended ionosphere, and we report the discovery of a polar plasma cavity whose formation process is discussed
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