Solar Forcing at Titan Within the Context of Cassini Observations

A brief review will be given of the response of planetary ionospheres to the input of energy from the Sun and from external sources such as the solar wind. Particular emphasis will be given to the role that superthermal electrons play in planetary ionospheres. Superthermal electron populations in planetary ionospheres include photoelectrons associated with the photoionization of atmospheric neutrals by solar EUV and soft x-ray radiation and external fast electrons from magnetospheres or from the solar wind. The ionosphere of Titan will be emphasized in this talk. The results of ionospheric model calculations of densities and superthermal electron fluxes will be compared with measurements made by a number of instruments onboard the Cassini Orbiter.