JUICE arrives at Jupiter
ESA’s icy-moons explorer JUICE is due to reach Jupiter in July 2031 after a cruise of about eight years. Its goal is to enter orbit around Ganymede in December 2034, becoming the first spacecraft to orbit a moon of a planet other than Earth.
Available views: Orbit ✓ · Sky — (not visible in the sky)
The story
JUICE is a large spacecraft sent to Jupiter by the European Space Agency (ESA). Its name is short for ‘JUpiter ICy moons Explorer’, and as the name says, its main job is to study the icy moons around Jupiter rather than the planet itself. Its targets are Ganymede, Callisto and Europa, and its final destination is Ganymede, the largest moon in the solar system. JUICE was launched on an Ariane 5 rocket on 14 April 2023.
The eight-year journey is not only about distance. A rocket alone cannot send this heavy spacecraft straight to Jupiter. So JUICE passes close to Earth and Venus several times, borrowing their gravity to gain speed. This is called a ‘gravity assist’ or ‘swing-by’: the spacecraft picks up speed as it swings past a planet, a little like a stone from a slingshot.
JUICE has already completed several of these swing-bys. In August 2024 it passed the Moon and then Earth a day apart; on 31 August 2025 it passed Venus; and on 28 September 2026 it passed Earth again. After one more pass by Earth in January 2029, the long journey out to Jupiter begins, and JUICE is due to enter orbit around Jupiter in July 2031.
Even after reaching Jupiter, JUICE will not head straight for Ganymede. For several years it will loop widely around Jupiter, passing Callisto many times and Europa twice. The plan is then to enter orbit around Ganymede in December 2034. The orbit view reproduces JUICE’s route as it gathers speed by swinging past Earth and Venus and then stretches out towards Jupiter.
Mission goals
Icy moons attract attention because oceans of liquid water may lie beneath their thick shells of ice. These moons are far from the Sun, so their surfaces are frozen solid. Jupiter’s strong gravity, however, squeezes and stretches them as they orbit, and this can warm their insides. Scientists think Ganymede may hold more water under its ice than all of Earth’s oceans put together.
Ganymede is special even among these moons. It is bigger than the planet Mercury, and it is the only moon known to make its own magnetic field. As a result, Ganymede’s small magnetic bubble sits inside Jupiter’s enormous one. To study this arrangement closely over a long time, a spacecraft needs to keep circling the moon rather than just fly past, and that is why JUICE aims to finish in orbit around Ganymede.
Being able to compare three moons with one spacecraft also matters. Europa’s surface is young ice covered in cracks, Callisto’s is very old ice covered in craters, and Ganymede lies somewhere in between. Why worlds made from similar material beside the same planet turned out so differently is a long-standing question, and measuring all three with the same instruments allows a fair comparison.
Mission chronology and background
So far only two spacecraft have circled Jupiter and studied it for years. Galileo, arriving in 1995, was the first to orbit the planet and gathered strong evidence for an ocean beneath Europa’s ice. Juno, arriving in 2016, has mainly studied Jupiter itself: its inner structure and its magnetic field. Before them, in the 1970s, the Pioneer and Voyager spacecraft flew past Jupiter and sent back the first detailed pictures.
JUICE moves the focus from Jupiter to its icy moons, and its instruments were chosen to match. It carries a radar that looks down into the ice, a laser altimeter that measures the height of the surface, cameras and spectrometers, and sensors for magnetic fields and the electrically charged particles around the moons. With them it will look for the thickness of the ice shells and signs of the oceans beneath.
Around the same time, NASA’s Europa Clipper is due to arrive at Jupiter. Europa Clipper will orbit Jupiter and study Europa during dozens of close passes. When two spacecraft observe the same moons in the same period from different directions and at different times, they can reach more reliable conclusions than either could alone.
Other milestones of this mission
Where to see it — sky and simulator
Arrival at Jupiter cannot be seen in the night sky, because the spacecraft is far too small and distant. The replay in the orbit view is the best way to follow the whole journey instead. Starting from the 2023 launch and running time forward reproduces, in order, the loops past Earth and Venus that gather speed and the long leg out to Jupiter. Pausing before and after each swing-by shows how the route changes.
Jupiter itself, the destination, is easy to see. When it is in the night sky it outshines most stars and shines with a calm light that twinkles little. Even small binoculars show four tiny points lined up beside it: the four moons Galileo first discovered. Watching over several nights shows the points changing places. Ganymede, Callisto and Europa, which JUICE will study, are among those points.
News of the mission comes from ESA. The agency has announced its plans before major swing-bys and released pictures and instrument checks afterwards. Key moments such as entering orbit around Jupiter are announced when antennas on Earth receive the signal. Radio waves take tens of minutes to travel from Jupiter to Earth, so the news always arrives a little late.
See this for yourself — replay the moment in the orbit view
FAQ
When does JUICE arrive at Jupiter?
It is due to enter orbit around Jupiter in July 2031. It will then spend several years passing Callisto and Europa, with a plan to enter orbit around Ganymede in December 2034.
Where is JUICE now?
It swung past Earth for the second time on 28 September 2026 to gain speed. After a final pass by Earth in January 2029, it heads for Jupiter.
Why is Ganymede the final destination?
Ganymede is bigger than Mercury and the only moon known to make its own magnetic field, and it may have an ocean under its ice. Circling it allows a long, close study rather than brief passes.
How is it different from Europa Clipper?
JUICE is an ESA mission focused on Ganymede and Callisto, ending in orbit around Ganymede. NASA’s Europa Clipper orbits Jupiter and makes dozens of passes by Europa.
Related
- JUICE launch (2023)
- Europa Clipper reaches Jupiter
- BepiColombo enters Mercury orbit
- Ganymede — object index
- Jupiter — object index
Times and figures are approximate — verify with official sources when planning travel. Simulation uses J2000 mean elements.