Titan's ionosphere: A review

This paper presents a concise review of our present understanding of the io nosphere of Titan and its interaction with the surrounding magnetosphere/ma gnetosheath of Saturn, based on observational constraints and theoretical m odel calculations. A variety of different models, as well as the Voyager 1 radio occultation re-analysis, indicate a peak electron density of about 2. 5-3.0 x 10(3) cm(-3), at an altitude just below 1200 km, for a solar zenith angle of near 90 degrees. Calculations predict that the ions near the elec tron density :peak consist mainly of HCNH+ and other more complex hydrocarb on ions. The lack of observational constraints on the electron and ion temp eratures leads to a wide range of possible values from the models, ranging from less than 1000 to nearly 10,000 degrees K. The Voyager 1 plasma measur ements in Titan's wake, combined with model calculations, have been used to estimate that the outward fluxes from the tail are on the order of 2-7 x 1 0(6) cm(-2) s(-1), corresponding to a total ion loss rate on the order of 1 0(25) s(-1). Published by Elsevier Science Ltd.