Observations of a structured ionospheric outflow plume at Titan

1. Observations of a structured ionospheric outflow plume at Titan EGU General Assembly Vienna, Austria 3-8 April 2011 Z66 EGU2011 1356 • Niklas Edberg, K. Ågren, J.-E. Wahlund, M. W. Morooka • IRF, Uppsala, Sweden • D. J. Andrews, S. W. H. Cowley • University of Leicester, UK • Wellbrock, A. J. Coates MSSL • University College London, UK • C. Bertucci • IAFE, Buenos-Aires, Argentina • M. K. Dougherty • Imperial College London, UK T59 T55 Abstract Recent results obtained from measurements by the Cassini Radio and Plasma Wave Science/Langmuir probe (RPWS/LP), magnetometer (MAG) and electron sensor (ELS) instruments are presented. We study the structured outflow of ionospheric plasma from the induced magnetosphere of Titan. During the final three of the five consecutive and similar Cassini Titan flybys T55 - T59 we observe a region characterized by high electron densities (1-8 cm-3) in the tail/night side of Titan. Both light and heavy ions with ionospheric composition are observed to travel away from Titan in this region. This region is observed progressively farther downtail from pass to pass and is interpreted as a plume of ionospheric plasma escaping Titan, which appears steady in both location and time. It extends to at least 6 Titan radii downstream of the moon. Magnetic field measurements indicate the presence of a current sheet at the inner edge of this region. We discuss the mechanism behind this outflow, and suggest that ambipolar diffusion, magnetic moment pumping or dispersive Alfvén waves could cause it. T58 T57 T56 Fig 7. Altitude profiles of the electron density measured during the inbound legs of the T55-T59 flybys. The observations of the electron plume are highlighted by the shaded regions. T55 Fig 6. Cassini flyby configuration for the T55-59 flybys (thin red lines). The thick red lines on top of the T55 and T56 tracks indicate the region of an extended ionosphere. The thick red lines on top of the T57, T58 and T59 tracks indicate the interval when the density plume is observed (see Figure 1-5). The blue lines show the average components of the magnetic field for each flyby. T56 T57 Summary Ionospheric plasma is observed to escape in a structured plume during the Cassini T55-T59 flyby. Ne = 1-8 cm-3 in the plume. The plume consists of light and heavy ions with composition indicating that it comes from Titan’s ionosphere. Ions move in direction away from Titan and hence are escaping. e- have isotropic distribution. The plume extends to > 6 RT behind the moon. T58 T59 Fig 1-5. Cassini RPWS, MAG, and ELS data from the T55-T59 flybys shown as a time series. The panels show from top to bottom: the LP voltage-current characteristics, LP measured Ne(blue) together with Ne derived from FUH emisions (red), LP measured Te, LP floating potential (cyan) and LP spacecraft potential (blue), MAG vector magnetic fields in TIIS coordinates, and an ELS electron spectrogram. References N.J.T. Edberg et al., Planet. Space. Sci, 2011 (in press) Acknowledgements NJTE was supported the Swedish Research Council. Contact: niklas.edberg@irfu.se