The observed composition of ions outflowing from Titan


Corresponding author: J. H. Westlake, Johns Hopkins Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD 20723, USA. (


[1] We report on Cassini Ion and Neutral Mass Spectrometer (INMS) observations above Titan's exobase at altitudes of 2225 km to 3034 km. We observe significant densities of CH5+, HCNH+ and C2H5+that require ion-molecule reactions to be produced in the quantities observed. The measured composition and ion velocity (about 0.8–1.5 km/s) suggest that the observed ions must have been created deep inside Titan's ionosphere (below the exobase) and then transported to the detection altitude. Plasma motion from below Titan's exobase to large distances can be driven by a combination of thermal pressure and magnetic forces. The observed outward flows may link the main ionosphere with the more distant wake and provide a source of hydrocarbon ions in the Saturnian system.