ESA Science & Technology - Cassini finds Northern Lakes on Titan

The extreme cold conditions at Titan, with surface temperatures around 94 K, allow for methane and ethane to exist in liquid form on the surface of the moon. Early models of Titan's atmosphere and chemistry predicted the existence of large lakes or even oceans on the moon's surface. Since October 2004, Cassini has made over twenty close flybys of Titan and has imaged different parts of the surface using radar to penetrate the thick atmosphere.

False-colour SAR image of radar-dark pathes around Titan's north pole Credit: NASA/JPL/USGS

The Titan flyby on 22 July 2006 presented the first opportunity for the Cassini Radar instrument to image the moon's high northern latitudes, which are currently in perpetual winter darkness. Using the radar in SAR mode (Synthetic Aperture Radar), a large strip, passing within 10° from the north pole, was obtained.

The portion above 73° latitude, depicted here in false-colour, reveals more than 75 radar-dark patches that contrast with the surrounding terrain. The patches are circular to irregular in shape and measure from 3 km to more than 70 km across.

Their dark appearance means the surfaces of these patches are very smooth. Together with the measured dielectric proporties and observed morphology, E.R. Stofan et al. conclude that the patches are liquid-filled lakes, most likely consisting of hydrocarbons.

Several of the lakes have sinuous features, also radar-dark, leading into them like channels. Some of the lakes are in relatively steep-sided circular depressions. Different depressions are filled in up to different levels. There are even surface features that have the same morphology as the lakes, but that appear empty, suggesting they have dried up.

Stofan, E.R. et al., The lakes of Titan, Nature, 445, 7123, pp. 61-64, http://dx.doi.org/10.1038/nature05438, 4 January 2007