Titan. These two views, taken on October 26th, 2004 (left) and April 16th, 2005 (right), are showing two adjacent regions of Titan, Saturn's main moon. Titan is one of the target of the joint NASA/ESA/Space Italian Agency Cassini mission, which arrived in the Saturnian world last July 2004. The main craft, Cassini, was carrying an European probe which descended into Titan's atmosphere on January 14th, 2005. Cassini is now continuing its comprehensive study of Saturn's environment and moons. Titan is both an icy moon -just like these moons found around all the gas giant planets- as it is the only moon in the solar system to have an atmosphere. It's these both elements which are explaining Titan's topology. Methane rain is playing at Titan the role water is playing at Earth, as erosion is acting upon ice instead of rocks. Titan is a world of eroded plateaus, elevated terrains with drainage chanels, and of fluvial relief. Ice-volcanism added too in the past, spewing water ice and ammonia. Titan's atmosphere, on the other hand, is where the Sun's ultraviolet light is creating hydrocarbon compounds from the methane and the nitrogen. Such compounds are seen like the "other way" life's building blocks are appearing in the Universe. It's such hydocarbon particles falling out onto the surface, and then washed away by rain down to the lower areas, which are giving their darker color to some regions of Titan. As the south pole is prominently tilted towards the observer, left, North, right, it tilted 30 degrees to the right. pictures NASA/JPL/Space Science Institute