Titan: High-resolution speckle images from the Keck Telescope

Saturn's large moon Titan is unique among planetary satellites in that it p ossesses a thick atmosphere and a haze layer that is opaque to visible ligh t. This haze is believed to be composed of organic compounds produced by th e photolysis of methane. It has been suggested that the photochemical produ cts of methane photolysis, primarily ethane, would "rain out" over time and may produce reservoirs of liquid hydrocarbons on Titan's surface. Such mat erial would appear very dark, with an albedo less than or equal to 0.02 (Kh are et al. 1990, Bull. Am. Astron, Sec. 22, 1033). Such low-albedo regions have not been previously detected on Titan's surface. Here we report observ ations of Titan at a resolution of 0.04 arcsec (0.02 arcsec/pixel) using th e technique of speckle imaging from the 10-m Keck I Telescope. By observing Titan at specific infrared wavelengths which are windows through its atmos phere, we have made both an albedo map of Titan's surface at 1.6 and 2.1 mu m and an estimate of Titan's haze optical depth at these wavelengths. We c learly distinguish low-albedo features (reflectance <0.05) on Titan's surfa ce. (C) 1999 Academic Press.