Turtle, E.P., McEwen, A.S., Dawson, D.D., West, R.A., Porco, C.C. (2004). "Cassini ISS Observations of the Surface of Titan During Approach to Saturn and the I0 Distant Flyby, April-July 2004." Eos Trans. AGU 85(28), West. Pac. Geophys. Meet. Suppl., Abstract P14A-03.


Abstract

On 2 April 2004, during Cassini's final approach to Saturn, the Imaging Science Subsystem (ISS, Porco et al., Space Sci. Rev., in press) began making observations of Titan's atmosphere and surface. At this time Cassini was 44.3 E 6 km from Titan and the pixel scale of ISS' narrow angle camera (NAC) was 270 km, comparable to that of Earth-based observations of Titan (e.g., Lemmon et al., Icarus 113, 1993, Smith et al., Icarus 119, 1996). The approach observations include filter combinations designed to take advantage of methane windows at near-infrared wavelengths to peer through Titan's haze to its troposphere and surface. These observations continue through 22 June 2004, with four specifically dedicated to acquiring coverage of most longitudes at pixel scales as good as 35 km. Models of Titan's haze predict that a small percentage of the light received from Titan should be unscattered reflectance from deep in the atmosphere, thereby allowing high-resolution imaging of the surface and/or troposphere. However, the optical properties of the troposphere are poorly known. The approach sequence will begin to reveal ISS' capability to observe Titan's surface. Shortly after Saturn orbit insertion, Cassini will have a distant encounter with Titan (2 July 2004), during which several observations are planned of the atmosphere and surface, including a 2x3 mosaic of Titan's South Pole at pixel scales as good as 2 km. This encounter will provide our best view to date of Titan and the first definitive test of the visibility of its surface at high resolution. Furthermore, it will be Cassini's best view of Titan's currently well illuminated South Pole. We will present the results and preliminary interpretations of these observations and discuss plans for the 44 close (less than 10,500 km altitude) Titan encounters planned during Cassini's 4-year nominal mission, which begin with a 1200 km altitude flyby on 26 October 2004.