Titan, once thought to be the largest moon in the solar system, turned out to be slightly smaller than Jupiter's moon Ganymede when photographed by Voyager 1. It is, nonetheless, larger than the planet Mercury. The surface of Titan is obscured by a dense atmosphere of nitrogen and methane, which made the moon appear larger in telescopic observations.
Although the atmosphere looks featureless when photographed from afar, some banding was detected in specially processed Voyager 1 images.
A color-enhanced image from Voyager 1 shows high altitude haze layers that occur 500 kilometers (310 miles) above the main cloud layer of Titan.
Voyager results indicated that Titan is more like Earth than any of the planets. The abundance of carbon components may make Titan a natural laboratory to study the most primitive organic chemical reactions that were present on Earth some 4 billion years ago.
Cassini Sees Through the Haze
With radar and spectrometers, Cassini was able to look through the thick haze of Titan's atmosphere and explore the terrain below. This infrared view shows dark dune-covered areas on the surface.
Cassini revealed that Titan is home to numerous large lakes filled with liquid methane and ethane. Clouds sometimes rain these hydrocarbons onto the surface. This radar image shows Ontario Lacus, one of the largest lakes on Titan. It shows evidence of river valleys draining into the lake and a possible delta formation.
Cassini carried the European Space Agency's Huygens probe which descended through Titan's atmosphere and successfully landed on the surface. On its descent it imaged this rugged terrain.
View of the surface from the Huygens probe.