Jupiter Icy Moons Explorer
The Jupiter Icy Moons Explorer is an interplanetary spacecraft developed by the European Space Agency and on its way to orbit and study three icy moons of Jupiter: Ganymede, Callisto, and Europa. These planetary-mass moons are planned to be studied because they are thought to have significant bodies of liquid water beneath their frozen surfaces, which would make them potentially habitable for extraterrestrial life.
Juice is the first interplanetary spacecraft to the outer Solar System planets not launched by the United States and the first set to orbit a moon other than Earth's Moon. Launched by ESA, from Guiana Space Centre in French Guiana on 14 April 2023, with Airbus Defence and Space as the main contractor, it is expected to reach Jupiter in July 2031 after four gravity assists and eight years of travel. In December 2034, the spacecraft will enter orbit around Ganymede for its close-up science mission. Its period of operations will overlap with NASA's Europa Clipper mission, which was launched in October 2024.
Background
The mission started as a reformulation of the Jupiter Ganymede Orbiter proposal, which was to be ESA's component of the cancelled Europa Jupiter System Mission – Laplace. It became a candidate for the first L-class mission of the ESA Cosmic Vision Programme, and its selection was announced on 2 May 2012.In April 2012, Juice was recommended over the proposed X-ray telescope ATHENA and the gravitational wave observatory LISA (under the older name NGO). Both unsuccessful mission proposals were selected later and are under development as of 2025.
In July 2015, Airbus Defence and Space was selected as the prime contractor to design and build the probe, to be assembled in Toulouse, France. In 2024, Airbus Defence and Space received the Excellence Award from ESA for their work on Juice. By 2023, the mission was estimated to cost ESA 1.5 billion euros.
Spacecraft
The main spacecraft design drivers are related to the large distance to the Sun, the use of solar power, and Jupiter's harsh radiation environment. The orbit insertions at Jupiter and Ganymede and the large number of flyby manoeuvres require the spacecraft to carry about of chemical propellant. The total delta-V capability of the spacecraft is about.Juice has a fixed 2.5 meter diameter high-gain antenna and a steerable medium-gain antenna; both X- and K-band will be used. Downlink rates of 2 Gb/day are possible with ground-based Deep Space Antennas. On-board data storage capability is 1.25 Tb.
The Juice main engine is a hypergolic bi-propellant 425 N thruster. A 100 kg multilayer insulation provides thermal control. The spacecraft is 3-axis stabilized using momentum wheels. Radiation shielding is used to protect onboard electronics from the Jovian environment.
The Juice science payload has a mass of and includes the JANUS camera system, the MAJIS visible and infrared imaging spectrometer, the UVS ultraviolet imaging spectrograph, RIME radar sounder, GALA laser altimeter, SWI submillimetre wave instrument, J-MAG magnetometer, PEP particle and plasma package, RPWI radio and plasma wave investigation, 3GM radio science package, the PRIDE radio science instrument, and the RADEM radiation monitor.
A deployable boom will hold J-MAG and RPWI, a long deployable antenna will be used for RIME. Four booms carry parts of the RPWI instrument. The other instruments are mounted on the spacecraft body, or for 3GM, within the spacecraft bus.
Mission timeline
Launch
Juice was launched into space on 14 April 2023 from the Guiana Space Centre on an Ariane 5 rocket. This was the final launch of an ESA science mission using the Ariane 5 vehicle, and the Ariane launches (2020–2029)|second to last launch of the rocket] overall.The launch was originally scheduled for 13 April 2023, but due to poor weather the launch was postponed. The next day a second launch attempt succeeded, with liftoff occurring at 12:14:36 UTC. After the spacecraft separated from the rocket, it established a successful radio signal connection with the ground at 13:04 UTC. Juice
During post-launch commissioning of the spacecraft, the RIME antenna failed to properly deploy from its mounting bracket. After several weeks of attempts to free the instrument, it was successfully deployed on 12 May of the same year.
Earth-Moon system flyby
In August 2024, Juice performed its first gravity assist when it flew by the Moon and then Earth, becoming the first ever spacecraft to perform such maneuver using both bodies. The closest approach to the Moon happened at 21:15 UTC on 19 August. This increased the spacecraft's speed by 0.9 km/s relative to the Sun, sending it towards Earth. The closest approach to Earth happened at 21:56 UTC on 20 August. This reduced the spacecraft's speed by 4.8 km/s relative to the Sun, sending it towards Venus for the next gravity assist planned for August 2025. This double gravity assist saved the spacecraft up to 150 kg of fuel and deflected it by an angle of 100° compared to its path before the flyby.During this maneuver, Juice tested many of its scientific instruments. All 10 instruments were active during the Moon flyby, and eight during the Earth flyby. The JANUS camera took high-resolution images of the Moon and Earth. The MAJIS and SWI instruments detected the expected chemical signatures of habitability on Earth and MAJIS also provided information-rich temperature maps of Earth. Two sensors of the Particle Environment Package took pictures and in situ measurements of the charged particle cloud surrounding Earth. The RIME radar sounder captured a radargram image of the patch of the lunar surface that is also visible in the famous Earthrise photo, taken in 1968 during the Apollo 8 mission.
Venus flyby
On 16 July 2025, during a time-sensitive period before the planned Venus flyby, Juice experienced a communication anomaly that temporarily severed the spacecraft's contact with Earth. After almost 20 hours of recovery efforts, ESOC and Airbus managed to resolve the issue and identified its root cause related to a scheduled restart of the spacecraft's internal timer. Plans for the flyby remained unchanged and Juice successfully flew by Venus on 31 August 2025, with the closest approach of 5,088 km above Venus's surface at 05:28 UTC, performing a gravity assist maneuver that increased its velocity by 5.1 km/s and sent it towards its second Earth flyby planned for September 2026. Due to thermal constraints, no imaging or scientific observations were planned for the Venus flyby and the spacecraft used its high-gain antenna as a thermal shield, pointing it toward the Sun.3I/ATLAS observations
The interstellar comet 3I/ATLAS, discovered in July 2025 as only the third known interstellar object in the Solar System, made its closest approach to the Sun in October 2025. However, this part of its trajectory, when it was expected to show strong cometary activity, was not visible from Earth-based telescopes as it occurred on the other side of the Sun. In September 2025, ESA expected that of all its interplanetary spacecraft, Juice would have the best conditions for observing the object during its close approach to the Sun.ESA commanded Juice to attempt observing 3I/ATLAS in November 2025, at a distance of 0.428 AU, using its cameras, spectrometers, and a particle sensor. ESA was also considering coordinating ultraviolet spectrograph observations with NASA's Europa Clipper. Due to the challenging thermal conditions during Juice
In early December 2025, ESA released a preliminary picture of 3I/ATLAS taken on 2 November 2025 by Juice
Trajectory
Following the launch, multiple gravity assists are needed to put Juice on a trajectory to Jupiter:- Flyby of the Earth–Moon system, in August 2024
- Venus flyby, in August 2025
- Second flyby of Earth in September 2026
- Third and final flyby of Earth in January 2029
Gravity assists within the Jovian system include:
- Jupiter orbit insertion and apocentre reduction with multiple Ganymede gravity assists
- Reduction of velocity with Ganymede–Callisto assists
- Increase inclination with 10–12 Callisto gravity assists
Jupiter mission phases
The main characteristics of the Jupiter reference tour are summarised below. This scenario assumed an early June 2022 launch, however, the delta-V requirements are representative due to the rather short, repetitive orbital configurations of Europa, Ganymede and Callisto.| Event | Duration | Delta-V notes |
| Jupiter orbit insertion: When it arrives in the Jovian system in July 2031, Juice will first perform a Ganymede gravity assist flyby to reduce spacecraft velocity by ~, followed by ~ Jupiter orbit insertion engine burn ~7.5 hours later. Finally, a Perijove Raising Manoeuvre burn at apoapsis will raise the periapsis of Juice | 186 days | . |
| 2nd Ganymede flyby to initial encounter with Callisto: 2nd, 3rd and 4th Ganymede flyby to reduce the orbital period and inclination of Juice | 193 days | . |
| Europa phase: Starting in July 2032, there will be two < flybys of Europa followed by another Callisto flyby. The brief Europa encounters are planned such that the radiation exposure is as low as possible, first by encountering Europa at perijove, and second by having only one low perijove passage per Europa flyby. | 35 days | . |
| Inclined phase: ~6 further flybys of Callisto and Ganymede to temporarily increase the orbital inclination to 22 degrees. This will allow an investigation of Jupiter's polar regions and Jupiter's magnetosphere at the maximum inclination over a four-month period. | 208 days | . |
| Transfer to Ganymede: A series of Callisto and Ganymede gravity assists will be performed to gradually reduce Juice | 353 days | . |
| Ganymede orbital phase: In December 2034, Juice will enter an initial 12-hour polar orbit around Ganymede after performing a delta-V braking burn. Jupiter gravitational perturbations will gradually reduce the minimum orbital altitude to after ~100 days. The spacecraft will then perform two major engine firings to enter a nearly circular polar orbit, for a further six months of observations. The orbital phase includes a final stage at 200 km altitude. At the end of 2035, Jupiter perturbations will cause Juice to impact onto Ganymede within weeks as the spacecraft runs out of propellant. | 284 days | . |
| Full tour | 1259 days | . |
Science objectives
The Juice orbiter will perform detailed investigations on Ganymede and evaluate its potential to support life. Investigations of Europa and Callisto will complete a comparative picture of these Galilean moons. The three moons are thought to harbour internal liquid water oceans, and so are central to understanding the habitability of icy worlds.Ganymede and Callisto
The main science objectives for Ganymede, and to a lesser extent for Callisto, are:- Characterisation of the ocean layers and detection of putative subsurface water reservoirs
- Topographical, geological and compositional mapping of the surface
- Study of the physical properties of the icy crusts
- Characterisation of the internal mass distribution, dynamics and evolution of the interiors
- Investigation of Ganymede's tenuous atmosphere
- Study of Ganymede's intrinsic magnetic field and its interactions with the Jovian magnetosphere.
Europa
For Europa, the focus is on the chemistry essential to life, including organic molecules, and on understanding the formation of surface features and the composition of the non-water-ice material. The chemical investigations will be focused also on the question which chemicals originated underground and were brought to the surface by tectonics or cryovolcanism, and which arrived from above, originating at other places within the Jovian system.Furthermore, Juice will provide the first subsurface sounding of the moon, including the first determination of the minimal thickness of the icy crust over the most recently volcanically active regions. Juice will be able to determine if pockets of liquid water exist within the ice and possibly also probe the interface between the icy shell and the subsurface ocean.