IntroductionFiled Under: Mission
Titan and Enceladus, satellites of planet Saturn, have been effectively revealed by the recent Cassini/Huygens mission. These two satellites are unique objects in our Solar System and the only ones so far to exhibit atmospheres amongst the sixty Kronian satellites. Titan, the largest Saturnian satellite, appears both similar and different exotic world, comparing with our living planet. According to the latest findings of the Cassini/Huygens mission, its nitrogen dominated thick atmosphere and its rugged surface have rocked not only the planetary scientists, but also the general public. The Saturnian System is a key target for Astrobiology. Titan and Enceladus could hardly seem more different, and yet they are linked by their origin in the Saturn system, by a magnetosphere that sweeps up mass and delivers energy, and by the possibility that one or both worlds harbor life. It is the goal of the NASA/ESA Titan Saturn System Mission (TSSM) to explore these exotic yet inviting worlds, to understand their natures, and assess their potential habitability.
The combination of multiple flybys by the Cassini spacecraft and the Huygens probe descent through Titan’s atmosphere and its landing on Titan’s surface has resulted in a considerable increase in our understanding of the Titan system (including its surface, atmosphere and the interaction which occurs with its surrounding plasma environment) as well as of the other icy satellites. The many discoveries which have been made are a major breakthrough to our understanding of these complex worlds, but several questions remain outstanding. These questions were the basis for the science objectives which motivated currently-studied future space mission to Titan. The science goals would be to provide information on such aspects as the composition of the surface and the geographic distribution of the various organic constituents ; on the methane cycle and the methane reservoirs ; on the ages of the surface features, and in particular on whether cryovolcanism and tectonism are actively ongoing or are relics of a more active past ; on the presence or absence of ammonia, of a magnetic field and of a sub-surface ocean ; on the chemistry that drives complex ion formation in the upper atmosphere ; and on a large altitude range in the atmosphere, from 400–900 km, which remains poorly explored after Cassini. In addition, much remains to be understood about seasonal changes of the atmosphere at all levels, and the long-term escape of constituents to space.
The Titan Saturn System Mission (TSSM) is an attempt to answer the outstanding questions and to bring new insights on Titan and its environment, in particular Enceladus and Saturn’s magnetosphere. It was created by the merging of the TandEM proposal and the Titan Explorer 2007 Flagship study. The latter featured a long-lived lander and a montgolfière (hot-air balloon) to be released from an orbiter (using aerocapture to brake into orbit around Titan). The mission’s lifetime was about a year. The Titan Explorer Flagship 2007 Study Report can be found on: http://www.lpi.usra.edu .
The ESA TandEM proposal included 155 scientists and engineers from all over the world led by A. Coustenis (LESIA, Paris-Meudon Observatory) and was originally submitted to ESA’s Cosmic Vision call as an L-class mission (budget within 650 MEuros) to explore in-situ both Titan and Enceladus in collaboration with NASA and ESA. The mission concept was built around an orbiter, a Titan aerial platform, Titan mini-probes and Enceladus penetrators/landers carrying a large variety of scientific instruments. The baseline mission was for two-moderately sized spacecraft to be launched around 2020; these spacecraft would use chemical propulsion and radioisotope power, while orbit insertion options such as aerocapture and aerobraking would be part of the assessment phase. The spacecraft were envisaged to consist of a Titan-Enceladus Orbiter (which would carry the Enceladus in-situ package, which consisted mainly of penetrators) and a carrier for the Titan in-situ elements (a montgolfière and up to three mini-probes).
The orbiter would first go into orbit around Saturn and then using cycler orbits make multiple flybys of Enceladus as well as deliver 2 penetrators to prime target sites on its surface. The orbiter would then go into orbit around Titan. Once the initial orbiter phase is completed its orbit would be circularized to prepare its support of the Titan probes which would arrive shortly afterwards. These probes would separate from their carrier and enter Titan’s atmosphere via aerocapture. The TandEM mission details can be found on the web site: http://www.lesia.obspm.fr/cosmicvision/tandem/index.php .