High-altitude charged aerosols in the atmosphere of Titan

Observations by several instruments onboard the Cassini spacecraft revealed the existence of heavy hydrocarbon and nitrile species with masses of several thousand atomic mass units in the ionosphere of Titan. These very large molecules are in fact aerosols. The goal of this paper is to compute the concentrations of the charged aerosols in the upper atmosphere (950–1200 km) of Titan. The charging of these aerosols has been studied using the charge balance equations, where positive ions, negative ions, electrons, neutral and charged aerosols are included. Number concentrations of charged aerosols are compared with those observed by the Cassini instruments. The present work estimates the aerosol mass density as 1–10 kg/m3, which is within the predicted range. The results show that the aerosols must be smaller than 10 nm in order to have reasonable agreement with observations by the Cassini Plasma Spectrometer.

► Aerosols in the ionosphere of Titan are mostly of radius less than 10 nm.
► Charged particles carry single charge when the radius is less than 32 nm.
► Aerosols at altitudes of 950–1120 km have a density of 1–10 kg/m3.