分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: The Saturn System has been studied in detail by the Cassini-Huygens Mission. A major thrust of those investigations has been to understand how Saturn formed and evolved and to place Saturn in the context of other gas giants and planetary systems in general. Two models have been proposed for the formation of the giant planets,the core accretion model and the disk instability model. The heavy element enrichment, core size, and internal structure of Saturn, compared to Jupiter strongly favor the core accretion model as for Jupiter. Two features of the core accretion model that are distinct from the disk instability model are the growth of a core with a mass several times that of the Earth, followed by runaway collapse of gas onto the core once a mass threshold is reached. The heavy element core grows slowly over millions of years through accretion of cm-m sized pebbles, even larger bodies, and moon sized embryos in the gaseous disk. The abundance pattern of heavy elements is thus a key constraint on formation models. C, N, S, and P at Saturn are presently known to varying degree of uncertainty. The He to H ratio in the atmosphere is crucial for understanding heat balance, interior processes, and planetary evolution, but present values at Saturn range from low to high, allowing for a wide range of possibilities. While the very low values are favored to explain excess luminosity, high values might indicate presence of layered convection in the interior, resulting in slow cooling. Additional insight into Saturn's formation comes from the unique data on the rings from Cassini's Grand Finale orbits. While the solar system is the only analog for the extra solar systems, detection of the alkali metals and water in giant exoplanets is useful for understanding the formation and evolution of Saturn, where such data are presently lacking.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: This chapter reviews for each province and destination of the Solar System the representative space missions that will have to be designed and implemented by 2061 to address the six key science questions about the diversity, origins, workings and habitability of planetary systems (described in chapter 1) and to perform the critical observations that have been described in chapters 3 and partly 2. It derives from this set of future representative missions, some of which will have to be flown during the 2041-2061 period, the critical technologies and supporting infrastructures that will be needed to fly these challenging missions, thus laying the foundation for the description of technologies and infrastructures for the future of planetary exploration that is given in chapters 5 and 6, respectively.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: The main objective of this chapter is to present an overview of the different areas of key technologies that will be needed to fly the technically most challenging of the representative missions identified in chapter 4 (the Pillar 2 Horizon 2061 report). It starts with a description of the future scientific instruments which will address the key questions of Horizon 2061 described in chapter 3 (the Pillar 1 Horizon 2061 report) and the new technologies that the next generations of space instruments will require (section 2). From there, the chapter follows the line of logical development and implementation of a planetary mission: section 3 describes some of the novel mission architectures that will be needed and how they will articulate interplanetary spacecraft and science platforms; section 4 summarizes the system-level technologies needed: power, propulsion, navigation, communication, advanced autonomy on board planetary spacecraft; section 5 describes the diversity of specialized science platforms that will be needed to survive, operate and return scientific data from the extreme environments that future missions will target; section 6 describes the new technology developments that will be needed for long-duration missions and semi-permanent settlements; finally, section 7 attempts to anticipate on the disruptive technologies that should emerge and progressively prevail in the decades to come to meet the long-term needs of future planetary missions.