The Jupiter Icy Moons Explorer (JUICE) mission, recently selected by ESA as the first large mission within the Cosmic Visions 2015-2025 plan, is being developed to address questions regarding the Jupiter system and its satellites, with a focus on the largest moon, Ganymede. By thoroughly exploring the system and thereby unravelling the history of its evolution, from initial formation of the planet to the development of its satellite system, we will gain a general understanding of how gas giant planets and their satellite systems form and evolve and of how our Solar System works. The overarching theme for JUICE is the emergence of habitable worlds around gas giants taking into account the necessary conditions involving the simultaneous presence of organic compounds, trace elements, water, energy sources and a relative stability of the environment over time. JUICE will thus address the question: Are there current habitats elsewhere in the Solar System with such necessary conditions to sustain life? The spatial extent and evolution of habitable zones within the Solar System are critical elements in the development and sustainment of life, as well as in addressing the question of whether life developed on Earth alone or whether it was developed or could develop in other Solar System environments. The focus of JUICE is to characterise the conditions that may have led to the emergence of habitable environments among the Jovian icy satellites, with special emphasis on the three ocean-bearing worlds, Ganymede, Europa, and Callisto.

Ganymede is identified for detailed investigation since it provides a natural laboratory for analysis of the potential habitability of icy worlds in general, but also because of the role it plays within the system of Galilean satellites, and its unique magnetic and plasma interactions with the surrounding Jovian environment. For Europa, two targeted flybys are planned, with a focus on the chemistry essential to life, including organic molecules, and on understanding the formation of surface features and the composition of the non water-ice material, leading to the identification and characterisation of candidate sites for future in situ exploration. Furthermore, JUICE will provide the first subsurface observations of this icy moon, including the first determination of the minimal thickness of the icy crust over the most recently active regions.

JUICE will determine the characteristics of liquid-water oceans below the icy surfaces of the moons. This will lead to an understanding of the possible sources and cycling of chemical and thermal energy, allow investigation of the evolution and chemical composition of the surfaces and of the subsurface oceans, and enable an evaluation of the processes that have affected the satellites and their environments through time. The study of the diversity of the satellite system will be enhanced with additional information gathered remotely on Io and smaller moons. The mission will also focus on characterising the diversity of processes in the Jupiter system which may be required in order to provide a stable environment at Ganymede, Europa and Callisto on geologic time scales, including gravitational coupling between the Galilean satellites and their long term tidal influence on the system as a whole. 

Focused studies of Jupiter’s atmosphere, and magnetosphere and their interaction with the Galilean satellites will further enhance our understanding of the evolution and dynamics of the Jovian system. The circulation, meteorology, chemistry and structure of Jupiter will be studied from the cloud tops to the thermosphere. These observations will be acquired over a sufficiently long temporal baseline with broad latitudinal coverage to investigate evolving weather systems and the mechanisms of transporting energy, momentum and material between the different layers. 

The mission scenario foresees arrival in the Jupiter system following orbit insertion, during which JUICE will perform a tour of the Jupiter system using gravity assists of the Galilean satellites to shape its trajectory. This tour will include continuous monitoring of Jupiter’s magnetosphere and atmosphere, two targeted Europa flybys, a Callisto flyby phase reaching Jupiter latitudes of 30°, culminating with the dedicated Ganymede orbital phase. The current end of mission scenario involves spacecraft impact on Ganymede. The JUICE mission is planned to be launched in mid-2022, with a backup opportunity in August 2023. It will arrive at Jupiter in January 2030 after 7.6-years using an Earth-Venus-Earth-Earth gravity assist sequence and is foreseen to last for 3 and a half years.