Spatially Resolved Images of Titan by Means of Adaptive Optics

Abstract

Images of Titan were acquired with the ADONIS adaptive optics system installed at the ESO 3.6-m telescope in La Silla (Chile). The near-infrared range from 1–2.5 μm was covered in 1994 and 1995 in the methane atmospheric windows at 1.3, 1.6, and 2.0 μm with narrow-band filters and CVF. Diffraction-limited images were obtained (0.14 arcsec at 2 μm), thus allowing us to resolve the Titan disk. We have corrected the images for systematic effects, removed center-to-limb variation, and applied deconvolution processes to our data. The contrast on the images is on the order of 30%. Both the leading and trailing hemispheres were observed. The 2-μm images presented in this paper show a broad bright feature on the surface of Titan's leading hemisphere (near 114° LCM), which is in agreement with the HST images and with spectroscopy performed at these longitudes from the ground that show a higher geometric albedo on Titan's leading side. High-quality flat fielding of our data has highlighted the presence of at least two main bright spots within the equatorial region. The trailing hemisphere of Titan's surface is not completely dark but shows brightness near the poles, with some north-to-south asymmetry. The northern latitudes are uniformly brighter than the lower equatorial and southern latitudes (factor of about 2). Our results bring new constraints on the models of the satellite's surface.