Jupiter’s ever-changing atmosphere has been a source of curiosity since the Solar System’s most famous storm – the churning Great Red Spot – was first glimpsed in the 17thcentury. Juice will use its unique instruments to answer questions such as: What is the weather and climate like on Jupiter? How does an atmosphere work when there is no solid surface? What could be making Jupiter’s upper atmosphere so unexpectedly hot?

As the most volcanically active body in the Solar System, Io will be another target for Juice. On this fiery world, volcanoes soar up to around 18 km in height, and eruptions can last years. These eruptions blast out charged particles that are carried around Jupiter and towards Ganymede and Europa. Juice will monitor Io’s volcanic activity and investigate what its surface is made of.Left: Galileo image of the asteroid Gaspra. Right: Galileo image of the asteroid Ida (at left) and its tiny satellite Dactyl.

Left: Illustration of Galileo in orbit around Jupiter. Right: Illustration by Ken Hodges of Galileo’s entry probe during its descent through Jupiter’s upper atmosphere. Juno was selected on June 9, 2005, as the next New Frontiers mission after New Horizons. [16] The desire for a Jupiter probe was strong in the years prior to this, but there had not been any approved missions. [17] [18] The Discovery Program had passed over the somewhat similar but more limited Interior Structure and Internal Dynamical Evolution of Jupiter (INSIDE Jupiter) proposal, [18] and the turn-of-the-century era Europa Orbiter was canceled in 2002. [17] The flagship-level Europa Jupiter System Mission was in the works in the early 2000s, but funding issues resulted in it evolving into ESA's Jupiter Icy Moons Explorer. [19] The next spacecraft to explore Jupiter, the JPL-managed Juno, arrived in polar orbit around the giant planet on July 4, 2016, and continues to return stunning images and scientific data. The European Space Agency plans to launch the JUICE (JUpiter ICy moons Explorer) in 2022 to arrive at Jupiter in 2029, make several flyby of several of the large moons, and finally enter orbit around Ganymede in 2032 for an in-depth study of that satellite. Under development at NASA, the Europa Clipper will launch in 2025 with arrival at Jupiter between 2026 and 2031, depending on the launch vehicle chosen. Once in orbit around Jupiter, Europa Clipper will make up to 45 flybys of its namesake satellite at altitudes as low as 16 miles to complete a comprehensive study. The two missions, JUICE and Europa Clipper, will conduct complementary investigations to greatly increase our knowledge of Jupiter and its satellites.Another interesting property of Io is its relationship with the orbits of Ganymede and Europa: for every orbit that Ganymede makes of Jupiter, Europa completes precisely two, and Io precisely four. It is likely that the three moons formed somewhere else around Jupiter and were captured into these stable orbits. Juice will help us understand how and why the moons’ orbits have changed over time. Another curious feature of Jupiter’s atmosphere is the auroras that light up the planet’s poles. Just like the auroras on Earth, these are caused by charged particles that are channelled along Jupiter’s magnetic field lines and collide with other molecules in the planet’s atmosphere. They look beautiful, but are a visible sign of chemical changes in Jupiter’s polar atmosphere. Juice will study the aurora to understand how the planet’s magnetic field and atmosphere interact over time.

How does this all come together? Artist impression of 25 ‘hot Jupiters’ – gas giant exoplanets that look physically similar to Jupiter but orbit closer to their host stars Galileo images of Jupiter’s four largest moons (left to right) Callisto, Europa, Ganymede, and Io – the satellites are not to scale.Juice’s main goal is to characterise Jupiter’s icy moons as both planetary objects and possible habitats. But by observing Jupiter’s atmosphere, magnetosphere, and system of moons and rings, the mission will also reveal how different aspects of the planet’s environment affect one another. In this way, Juice will improve our knowledge of Jupiter as a unique planet and as a whole system.

The orbiter fired its main engine on Dec. 7, 1995, becoming the first artificial satellite of Jupiter with an initial orbital period of 198 days. Galileo soon began its nominal two-year science mission during which it completed 11 orbits around Jupiter. Mission planners designed these trajectories to optimize studies of Jupiter’s magnetosphere and to enable encounters with Jupiter’s largest moons Callisto, Europa, and Ganymede. Galileo also studied Jupiter’s ring system, composed largely of dust derived from impacts with the planet’s four small inner moons Thebe, Amalthea, Adrastea, and Metis, as well as the Great Red Spot and other atmospheric phenomena. On Dec. 7, 1997, NASA managers approved the two-year Galileo Europa Mission (GEM) extension that included eight consecutive encounters with Europa to study that moon’s frozen surface in great detail. As part of the GEM, Galileo also observed Io during two close encounters and Callisto during four flybys. The Galileo Millennium Mission extension added first one more year of observations then continued until the mission’s conclusion, and included more flybys of Ganymede and Io and joint observations with the Cassini spacecraft as it completed a flyby of Jupiter in December 2000 as a gravity-assist maneuver on its way to Saturn. Galileo completed its final encounter when in November 2002 it flew by the small inner moon Amalthea, providing important information about the satellite’s density. In addition to that final encounter, Galileo had completed seven flybys of Io, eight each of Callisto and Ganymede, and 11 of Europa. Four images taken by Galileo several seconds apart showing the impact of one of Comet Shoemaker-Levy 9’s fragments on Jupiter’s night side. Left: Illustration of the Juno spacecraft firing it main engine. Right: Image of Jupiter taken by Juno. Galileo made the first close-up observations of an asteroid during a flyby of 12-mile long 951 Gaspra. Flying within 997 miles of the asteroid on Oct. 29, 1991, Galileo returned much science data and 150 photographs. A second flyby of the Earth took place on Dec. 8, 1992, with Galileo coming within 188 miles of its home planet. The spacecraft now had the required velocity to head toward Jupiter. Along the way, Galileo explored its second asteroid, flying within 1,500 miles of 35-mile long 243 on Aug. 28, 1993. The spacecraft made the surprising discovery that Ida had a tiny companion, the 1-mile wide satellite Dactyl orbiting about 90 miles away, the first known moon orbiting around an asteroid.

Juno completed a five-year cruise to Jupiter, arriving on July 5, 2016. [7] The spacecraft traveled a total distance of roughly 2.8 × 10 Juice’s entire arsenal of instrumentation will also tell us more about the Great Red Spot. Although it has been raging for hundreds of years, we can see from Earth that this huge storm is shrinking and starting to interact with other storms. To really understand this new phase of existence, Juice will look at how the storm changes over many years. Inside the Great Red Spot, gases are ‘cooked’ by ultraviolet rays from the Sun to form potentially unique molecules; Juice will use spectroscopy (looking at the wavelengths of light being absorbed and emitted by molecules inside the storm) to uncover the strange chemical processes taking place and the origins of those striking red colours. This discussion of auroras, charged particles and magnetic fields takes us on to Jupiter’s magnificent magnetic environment. Magnetic environment In total, Jupiter is surrounded by almost 80 moons, as well as rings of tiny dust particles. Whilst Saturn’s rings shine loud and clear, it wasn’t until 1979 that Jupiter’s more subtle ring system was discovered by astronomers. The age of these rings is still unknown, but various processes in Jupiter’s fierce environment destroy small dust particles, meaning that something must be constantly replenishing the rings if they are to live for very long. Some of the charged particles reach Jupiter’s icy moons (Ganymede, Europa and Callisto), where they alter the moons’ atmospheres and surface composition. But the nature of these interactions remains a mystery.