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E.P. Turtle, A.S. McEwen, J. Perry, S. Campbell, D.D. Dawson (Univ. of Arizona), R.A. West, T.V. Johnson (JPL), C.C. Porco (Space Sci. Inst.), Cassini ISS Team
Cassini's Imaging Science Subsystem (ISS) began making systematic observations of Titan on 2 April 2004 with a three-month-long approach sequence that included filter combinations designed to take advantage of methane windows at near-infrared wavelengths to peer through Titan's photochemical haze to its troposphere and surface. Over this time the pixel scale improved from 270 km to 35 km. The resulting surface map, which has near-global coverage (except for the unilluminated North (winter) pole), is similar to, but sharper than, earlier Earth-based observations. Low-albedo features with scales of 100 km, some with strikingly linear boundaries, are seen near the equator, whereas mid-latitudes appear more uniformly bright.
Shortly after Saturn orbit insertion, Cassini had a distant encounter (339,000 km) with Titan, during which several mosaics of the South-polar region were acquired. These mosaics resolved intriguing surface features as small as 10 km. The variety of patterns suggests that geologic processes other than impact cratering alone have shaped Titan's surface, but the nature of these processes (e.g., tectonics, or erosion or deposition by liquids or winds) is not yet clear. No evidence of specular reflections, expected if liquids are present on the surface and unobscured, has been detected to date.
On 26 October 2004, Cassini will have its first close encounter with Titan (1200 km altitude at closest-approach), during which several more ISS mosaics, including the first high-resolution (pixel scales less than 500 m), are planned. ISS' coverage will include the specular point and the predicted location of the Huygens probe's landing site.
We will present these observations and preliminary interpretations, and discuss plans for the 43 remaining close (less than 10,500 km altitude) Titan encounters planned during Cassini's 4-year nominal mission.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.