1 Introduction: Titan viewed from Earth

The exploration of the solar system has become an important part of the glory and dreams of our civilization. The study of the Saturnian system and Titan itself can be traced back more than 400 years to when Galileo first pointed his telescope to the night sky to seek the mysteries of the universe. The Cassini-Huygens mission represents the first time in human history that a spacecraft was sent to spend time in the Saturnian system for close-up observations, bringing humanity to the surface of one of Saturn's satellites. We believe that this extraordinary achievement will be remembered as a major milestone in planetary exploration 400 years from now. More than that, it is also the first planetary science project of truly global scale, with scientists from three continents joining the effort. How did it come about?

To begin, let us first summarize what we knew about Titan before the birth of the Cassini-Huygens mission. Comprehensive descriptions of Titan studies during the period from its discovery in 1655 to the landing of the Huygens probe in 2001 have been published by Fortes (1997) and Coustenis et al. (2009). Here we simply present a few highlights in chronological order.