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Spatially Resolved Observations of an Upcoming Titan Occultation

1. BACKGROUND AND PROJECT OBJECTIVES In 1989 Titan briefly moved in front of 28 Sgr, a 6th magnitude star, an event that was observed from over 20 telescopes in Europe and Asia. The resulting data set (a collection of lightcurves of the disappearing and reappearing star) has proven to be a watershed event in our understanding of Titan's vertical temperature profiles, zonal wind fields and haze distributions. We request time on the AEOS 3.67-m telescope as part of a similar campaign to observe a stellar occultation predicted for 20 December 2001 (UT). Titan's atmosphere is predominantly nitrogen with traces of methane and other hydrocarbons and aerosols. Titan's surface pressure is only 50% larger than that of the Earth's, but Titan's lower surface gravity results in a much more extended (and ten times more massive) atmospheric column. Because methane and aerosols dominate the opacity of Titan's atmosphere in visible and near IR wavelengths, Voyager's vidicon cameras (operating at 0.6 μm or shorter) were unable to see below Titan's stratosphere (or roughly 150 km). During its 1981 flyby, Voyager did image an asymmetrical distribution of aerosols at higher altitudes (Fig. 1), and this asymmetry has been seen to change radically on a 16-year timescale (Fig. 2). One the the difficult questions to address is where the hazes are formed and how they are transported. Stellar occultations are one of the only techniques that can probe Titan's upper atmosphere, where the haze particles are initially formed by the UV photolysis of hydrocarbons in a nitrogen environment.