ESA’s Jupiter Icy Moons Explorer – Juice – will catch its first glimpse of ancient, cratered Callisto in June 2032, going on to whizz past the moon 21 times before making a final flyby in 2034. During these close encounters, Juice will collect valuable scientific treasure about the moon.

Callisto was first seen by Galileo in 1610 – what he thought were stars close to Jupiter were actually moons! Humanity has since revealed lots of information about the pockmarked moon. But there is still much to learn…

Previous observations by NASA’s Galileo mission suggest that Callisto has a below-the-surface ocean. However, its surface is very old and appears not to have been geologically active for a billion years or so, and so it is unclear if the moon has any ongoing internal dynamics.

Callisto is also the least geologically evolved Galilean satellite, and therefore offers our intrepid spacecraft a unique glimpse into the environment around early Jupiter. As Callisto does not seem to have evolved much over time, it stands to reveal unique information about how it initially formed, and about the origin of the wider Jupiter system.

Juice will investigate Callisto as a remnant of the early Jovian system by…

• …exploring its outer shell and ocean to constrain its interior structure and gravity;
• …characterising the composition and chemistry of its surface, especially any non-water-ice compounds, and identifying how Callisto releases material to space;
• …hunting for signs of past activity and determining how this connects to both its past evolution and the surface features we see today (such as Callisto’s characteristic dark, densely cratered plains, which show signs of unique erosion and degradation processes). Juice will image Callisto on both regional and global scales to achieve this.

As well as enabling us to carry out close-up science, some of Juice’s flybys of Callisto will also change the angle of Juice’s orbit with respect to Jupiter’s equator, making it possible to investigate the giant planet's polar regions and environment at higher latitudes.

Discover more about Juice and Jupiter’s icy moons.

ESA’s Jupiter Icy Moons Explorer, Juice, is humanity’s next bold mission to the outer Solar System. It will make detailed observations of gas giant Jupiter and its three large ocean-bearing moons – Ganymede, Callisto and Europa. This ambitious mission will characterise these moons with a powerful suite of remote sensing, geophysical and in situ instruments to discover more about these compelling destinations as potential habitats for past or present life. Juice will monitor Jupiter’s complex magnetic, radiation and plasma environment in depth and its interplay with the moons, studying the Jupiter system as an archetype for gas giant systems across the Universe.  

Juice launches on an Ariane 5 from Europe’s Spaceport in Kourou in April 2023. It has an eight year cruise with flybys of Earth and Venus to slingshot it to Jupiter. It will make 35 flybys of the three large moons while orbiting Jupiter, before changing orbits to Ganymede.

Juice is a mission under ESA leadership with contributions from NASA, JAXA and the Israeli Space Agency. It is the first Large-class mission in ESA’s Cosmic Vision programme.