English: As the name suggests, a strong focus of ESA’s Jupiter Icy Moons Explorer (Juice) is to explore the subsurface oceans of Jupiter’s icy moons. But an investigation into how life-friendly worlds form around gas giants would be incomplete without also studying Jupiter's turbulent atmosphere, its enormous magnetic field, and the dusty rings and myriad smaller moons that orbit the planet.
Atmosphere: 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 17th century. Juice will use four 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?
Magnetic environment: Jupiter’s complex magnetic environment is one of the Solar System’s outstanding mysteries. The planet’s rapidly rotating metallic liquid hydrogen core generates a magnetic field, which is thought to be 20 times stronger than that of Earth, and one million times larger in volume. Juice will study the region of space around Jupiter that is dominated by this magnetic field – the magnetosphere – to discover how the harsh environment shaped and continues to shape conditions on the icy moons.
Volcanic Io and Jupiter’s invisible rings: Aside from the large icy moons that Juice will get close to and explore in depth (Ganymede, Europa and Callisto) Juice will also observe the fourth ‘Galilean moon’ – eruptive Io – from a distance. 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.
Dusty rings and smaller moons: 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. By imaging the rings in 3D from different angles, and analysing them in various wavelengths of light to find out what exactly they are made of, Juice will help us understand more about their physics and chemistry.
See these four elements of the Jovian system in context in the first part of this infographic. Discover more about Jupiter and its complex environment in our dedicated article.

Juice will make detailed observations of Jupiter and its three large ocean-bearing moons – Ganymede, Callisto and Europa – with a suite of instruments. The mission will characterise these moons as both planetary objects and possible habitats, explore Jupiter’s complex environment in depth, and study the wider Jupiter system as an archetype for gas giants across the Universe.