Titan's surface and rotation: new results from Voyager 1 images

We present an analysis of images of Saturn's moon Titan, obtained by the Voyager 1 spacecraft on November 8-12, 1980. Orange filter (590-640 nm) images were photometrically corrected and a longitudinal average removed from them, leaving residual images with up to 5% contrast, and dominated by surface reflectivity. The resultant map shows the same regions observed at 673 nm by the Hubble Space Telescope (HST). Many of the same albedo features are present in both datasets, despite the short wavelength (600 nm) of the Voyager 1 images. A very small apparent longitudinal offset over the 14 year observation interval places tight constraints on Titan's rotation, which appears essentially synchronous at 15.9458 [+ or -] 0.0016 days (orbital period = 15.945421 [+ or -] 0.000005 days). The detectability of the surface at such short wavelengths puts constraints on the optical depth, which may be overestimated by some fractal models. Keywords: Titan, surface, atmosphere; Satellites; Image processing