Jupiter, the King of Planets, is so enormous that it can hold all of the other planets plus the asteroids, Kuiperoids, and comets and still have room to spare. It is ten times larger than Earth and has weather where winds howl over 400 miles per hour with hurricanes that are larger than Earth raging for centuries. Lightning is so powerful that it could span a continent and vaporize a city. Radiation is so intense that it would kill a person instantly and permanently disable spacecraft. The sheer size and power of Jupiter dominates the Solar System in that its gravity tugs at everything and can redirect comets, asteroids, spacecraft or anything that approaches too close to it. Jupiter is even responsible for altering the Solar System's structure by modifying other planetary orbits and creating and maintaining the asteroid belt. With such brute force, Jupiter deserves respect, and this makes it a desired target of increasing study.

The Voyager 1&2 flybys of 1979 were an eye-opener revealing the violent storms on Jupiter, deadly and complex radiation belts, active volcanoes on Io, possible underground ocean on Europa, fractured terrain on Ganymede, and craters everywhere on Callisto. Plans for an orbiter mission to Jupiter were well under way at that time, but the Challenger disaster in January 1986 delayed NASA's Galileo orbiter launch until October 18, 1989; it was switched to a less-powerful booster rocket for safety reasons regarding the Space Shuttle. It had to follow a long, torturous route, finally reaching Jupiter on December 7, 1995 and deployed a probe into Jupiter's atmosphere that studied the clouds, weather, and chemical composition for 75 minutes. Galileo orbited Jupiter until it burned up in its atmosphere on September 21, 2003 as it ran low on fuel as expected. It made several discoveries and studied Jupiter and its moons in exquisite detail in spite of a flawed main antenna. It confirmed the presence of a vast ocean beneath Europa's icy and unusually smooth crust, an oxygen atmosphere and magnetic field at Ganymede, ice pillars and landslides on Callisto, and the dynamic volcanic eruptions and lava flows on Io. Jupiter's complex cloud system and magnetic field were studied, especially the aurora and lightning, and the interaction of the solar wind with Jupiter's environment.

In spite of the successes of Galileo, Jupiter itself was not studied in as great detail as scientists would have liked because Galileo had to stay far away from it, primarily beyond Io's orbit, to avoid the intense radiation that would disable it. The probe only sampled Jupiter's upper atmosphere and only survived for 75 minutes as it fell through the Jovian atmosphere. Plus it fell into a dry slot, missing the moisture-rich clouds. Many questions remained and new ones emerged. Another orbiter was needed and NASA's Juno was born. Juno was launched on August 5, 2011 and is well on its way to Jupiter where it will arrive on July 4, 2016. It will go into polar orbit, well below the dangerous radiation, and as close as 2700 miles above the cloud tops. It will map the magnetic field and measure the number of charged particles interacting with the atmosphere that generate the dynamic aurora. Onboard instruments will penetrate deep into Jupiter's atmosphere to measure the internal convection along with the amount of water, ammonia, and methane, and try to determine why the Great Red Spot is red and what dynamics have kept it going for at least 400 years. Measurements of temperature and wind velocities at different levels may help elucidate what drives and maintains the huge storms. Juno will continue to orbit Jupiter until October 16, 2017 when it will burn up in its atmosphere. It will not study any of the moons during its mission as it will be orbiting too close to Jupiter while imaging. The need to study the large moons: Io, Europa, Ganymede, and Callisto have driven planetary scientists to develop another orbiter mission that will be the most complex mission ever to fly to any planet.

JUICE (Jupiter Icy Moon Explorer) is the next sophisticated spacecraft to be launched to Jupiter. It is being built and managed by the European Space Agency (ESA). This $1.1 billion mission will perform a detailed investigation of Jupiter and its system with special emphasis on Ganymede as a planetary body and potential habitat because it has a weak magnetic field and very thin oxygen atmosphere besides its deep interior ocean. The main science objectives for Ganymede are: characterize the ocean layers and subsurface water reservoirs, mapping of the geology and mineral composition of the surface, study the physical properties of the icy crust, characterize the mass and interior structure, investigate the very thin atmosphere, and study the magnetic field.

JUICE will also investigate Europa and Callisto, but Io lies too deep within the dangerous radiation belt to approach closely. Europa, Ganymede, and Callisto are believed to contain internal oceans, which is important in understanding the habitability of those icy worlds. Understanding Jupiter and its history from its origin to the potential emergence of habitable environments will give better insight into how gas giant planets and their satellites form and evolve around other stars. This will give a better idea on the possibility of the emergence of life in Jupiter-like exoplanets systems.

JUICE will also intensely study Jupiter's atmosphere by investigating its structure, dynamics, and composition. The circulation, meteorology, chemistry, and structure of Jupiter will be studied to investigate evolving weather systems and how energy is transported between different layers. The magnetic field, aurora, and lightning will be explored. JUICE will be powered by solar arrays and will carry the most powerful suite of instruments ever flown to Jupiter. It will include a laser altimeter to measure tidal deformation of Ganymede and ice penetrating radar. There will also be cameras (visible, infrared, and ultraviolet), a magnetometer, particle package, spectrometer, and other instruments to measure the environment around Jupiter, Ganymede, Europa, and Callisto.

The flight and overall mission for JUICE will be complex. It will launch in June 2022 aboard the reliable Ariane 5 and will use Venus and Earth for gravity assists for arrival at Jupiter in January 2030 where it will initially orbit Jupiter for a little over 2 and one-half years. It will continuously observe Jupiter's atmosphere and magnetosphere. JUICE will make several flybys of Ganymede and Callisto and two of Europa. Extensive observations will be made of these moons before JUICE enters into orbit around Ganymede in September 2032. JUICE will orbit Ganymede, the first spacecraft ever to orbit a moon around another world, as close as 120 miles near the final phase of its mission with it crashing into the surface in June 2033. If the spacecraft remains healthy, the mission could last until June 2034.

Jupiter is an important planet to explore considering its size and the influence it has on the other planets. Understanding its history and evolution is critical in determining if/how life could potentially evolve on its icy moons, and how it may have affected the development and evolution of life here on Earth. JUICE is a spacecraft that will address these matters and will attempt to fill in critical gaps with new knowledge on the possibility of the emergence of life on icy worlds.