The Jupiter Icy Moons Explorer (Juice, formerly JUICE) is an interplanetary spacecraft developed by the European Space Agency (ESA). It is on its way to orbit and study three icy moons of Jupiter: Ganymede, Callisto, and Europa. These planetary-mass moons are targets for study 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 intended 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 (EJSM-Laplace). It became a candidate for the first L-class (Large) mission (L1) 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 ($1.6 billion).
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 (more than 25 gravity assists, and two Europa flybys) 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 (mono-methyl hydrazine and mixed oxides of nitrogen) 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 required radiation tolerance is 50 kilorad at equipment level).
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 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's solar arrays were deployed about half an hour later, prompting ESA to deem the launch a success.
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 (PEP) 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 (solar flux of 3,000 W/m2 near Venus versus 50 W/m2 near Jupiter), 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.Flyby success! ESA's Juice spacecraft passed Venus at 07:28 CEST on 31 August.
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. Because Juice had to point its high-gain antenna towards the Sun to act as a heat shield during its travel through the inner Solar System, known as "hot-cruise phase", the data from these observations were not expected to reach Earth before February 2026. The commands for the observations were prepared at ESOC.
The observations were conducted between 2 and 25 November 2025. Thermal constraints were expected to limit the observations to no more than 30 minutes per day with the exception of the Particle Environment Package (PEP) which was commanded to operate for twelve days straight. The final observation schedule included six 45-minute slots and one final 4-hour slot. The observations generated 11.18 Gbits of data. The closest approach between the comet and the spacecraft happened on 4 November 2025.
In early December 2025, ESA released a preliminary picture of 3I/ATLAS taken on 2 November 2025 by Juice's Navigation Camera (NavCam). The photo included the comet's coma as well as the plasma and dust tails. The spacecraft entered the "cold-cruise phase" of its flight in mid-January 2026 and the observation data from five instruments—JANUS, MAJIS, SWI, PEP, and UVS—arrived on Earth in two 11-hour passes on 17 and 20 February 2026 via ESTRACK's antennas in New Norcia and Malargüe. The 3I/ATLAS observation campaign officially ended on 20 February 2026 at 18:21 UTC. ESA released the first one of more than 120 images of 3I/ATLAS taken by the JANUS camera system on 26 February 2026.
On 2 April 2026, ESA released first preliminary scientific results from the observations. The MAJIS instrument measured that on 2 November 2025, 3I/ATLAS was releasing 2000 kg of water per second and this amount hadn't diminished significantly in observations 10 days later, on 12 November 2025. The SWI instrument detected that most of the water was being released from the Sun-facing side of the comet and a substantial part of it came from icy dust grains of the coma, and not directly from the nucleus. The UVS images also revealed that the gas and dust from the comet stretched at least 5 million km from the nucleus. The JANUS images revealed faint structures within the comet's coma and two tails.
In early March 2026, when Juice no longer needed to use its high‑gain antenna as a Sun shield, ESOC performed a series of planned pointing checkout tests on the spacecraft's instruments, software updates, operations exercises, and commissioning activities.
Kallichore flyby decision
In July 2026, a team led by the Institute of Astrophysics of Andalusia published a detailed characterization of Jupiter's irregular moon Kallichore, providing data for a future decision whether to command Juice to perform a close flyby of the object in October 2031. The analysis included data from a stellar occultation by Kallichore on 15 December 2025.
Second Earth flyby
On 28 September 2026, Juice performed a gravity assist maneuver by flying by Earth. The closest approach happened 8640 km above the Indian Ocean at 11:45 UTC. The flyby deflected the spacecraft by 20° and increased its velocity by 3.5 km/s. Mission scientists coordinated Juice's observations of Earth's magnetotail with those of SMILE, launched only four months before, closer to the planet.
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 Flyby of Venus, in August 2025 Second flyby of Earth, in September 2026 Third and final flyby of Earth in January 2029
Juice will pass through the asteroid belt twice. A flyby of the asteroid (223) Rosa was proposed to occur in October 2029, but was removed from the mission plan to save fuel for the primary Jovian mission.
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