Saturn Satellites as Seen by Cassini Mission

In this paper we will summarize some of the most important results of the Cassini mission concerning the satellites of Saturn. The Cassini Mission was launched in October 1997 on a Titan IV-Centaur rocket from Cape Canaveral. Cassini mission was always at risk of cancelation during its development but was saved many times thanks to the great international involvement. The Cassini mission is in fact a NASA-ESA-ASI project. The main effort was made by NASA, which provided the launch facilities, the integration and several instruments; ESA provided the Huygens probe while ASI some of the key elements of the mission such as the high-gain antenna, most of the radio system and important instruments of the Orbiter, such as the Cassini Radar and the visual channel of the VIMS experiment. ASI contributed also to the development of HASI experiment on Huygens probe. The Cassini mission was the first case in which the Italian planetology community was directly involved, developing state of the art hardware for a NASA mission. Given the long duration of the mission, the complexity of the payload onboard the Cassini Orbiter and the amount of data gathered on the satellites of Saturn, it would be impossible to describe all the new discoveries made, therefore we will describe only some selected, paramount examples showing how Cassini’s data confirmed and extended ground-based observations. In particular we will describe the achievements obtained for the satellites Phoebe, Enceladus and Titan. We will also put these examples in the perspective of the overall evolution of the system, stressing out why the selected satellites are representative of the overall evolution of the Saturn system. Cassini is also an example of how powerful could be the coordination between ground-based and space observations. In fact coordinated ground-based observations of Titan were performed at the time of Huygens atmospheric probe mission at Titan on 14 January 2005, connecting the in situ observations by the probe with the general view provided by ground-based measurements. Different telescopes operating at different wavelengths were used, including radio telescopes (up to 17-tracking of the Huygens signal at 2040 MHz), eight large optical observatories studying the atmosphere and surface of Titan, and high-resolution infrared spectroscopy used to observe radiation emitted during the Huygens Probe entry (Witasse et al. J. Geophys. Res. 111:E07S01, 2006).