The European Space Agency’s Juice spacecraft completed a gravity-assist flyby of Earth on September 28, 2026, skimming the upper atmosphere above the Indian Ocean to accelerate toward Jupiter using minimal fuel while testing onboard science instruments.
The Jupiter Icy Moons Explorer passed 8,640 kilometers above the Indian Ocean at its closest approach at 13:45 CEST on September 28, 2026, according to Esa. The encounter deflected the spacecraft’s trajectory by 20 degrees and increased its velocity by 3.5 kilometers per second.
Fuel Conservation and Trajectory Adjustments Over the Indian Ocean
Using planetary gravity allows missions to achieve velocities that would otherwise require prohibitive propellant reserves. The JUICE spacecraft launched in April 2023 on an Ariane 5 rocket from Europe’s Spaceport in Kourou, French Guiana, and has relied on sequential planetary flybys rather than a direct trajectory to reach the outer solar system. During the flyby, Juice came within 5,370 miles of Earth and made its closest approach at 7:45 am ET, operating above the Indian Ocean as monitoring cameras captured Africa, Madagascar, and the Moon. The 13,381-pound spacecraft skimmed the very outer edge of Earth’s atmosphere, stealing momentum from our planet and gaining roughly 2.2 miles per second of speed without burning a single drop of its own fuel. The manoeuvre bent the spacecraft’s path by 20 degrees and accelerated it by about 7,800 mph.
The flyby required ultra-precise navigation in real time.
Angela Dietz, Spacecraft Operations Manager
Angela Dietz also stated that thanks to careful planning, the team used only a small amount of the propellant reserved for the flyby, which leaves more propellant available for observations when Juice reaches Jupiter and carries out studies of the planet’s icy moons. Retaining onboard propellant reserves ensures the spacecraft will have sufficient fuel remaining to enter orbit around Jupiter in July 2031 and subsequently transfer to an orbit around the Jovian moon Ganymede in 2034. Without gravity assists from Earth, Venus, and the Moon, a direct flight path would have demanded far heavier initial mass and much larger fuel reserves for braking upon arrival.
Juice Calibrates Instruments for Future Moon Flybys
Beyond altering the probe’s trajectory, the encounter served as a technical rehearsal for Juice’s 10 scientific instruments under real space environmental conditions. Mission scientists prioritized calibration activities relevant to future operations around Jupiter’s icy moons. Preparations for those encounters started years ahead of time, and the spacecraft is slated to perform 35 flybys of Ganymede, Callisto, and Europa, the giant planet’s major moons.
Juice’s journey to Jupiter provides only a few opportunities to calibrate and validate the instruments under well-understood environmental conditions.
Claire Vallat, Juice Project Scientist
While pointing out that every flyby carries inherent risks and demands rigorous oversight and continuous tracking, Claire Vallat observed that the September 2026 Earth encounter was operationally much more straightforward than the 2024 lunar-Earth maneuver, where passing the Moon initially positioned Juice for an Earth flyby the very next day. During the flyby sequence, Juice spent several days traveling through Earth’s magnetotail, the trailing extension of the planet’s magnetic field, allowing controllers to measure magnetic fields and charged particles. Colleagues from ESA’s spacecraft operations, science operations, and technical centres spent months working with external teams on Juice’s 10 science instruments to plan which instruments to switch on and when.
Prior Gravity Assists and the Route to Ganymede
The mission has utilized multiple planetary encounters to shape its orbit since leaving Earth in 2023. Those milestones include a lunar-Earth double flyby in August 2024 and a Venus gravity assist in August 2025. The spacecraft flew past Venus at an altitude of 3,162 miles, adding approximately 3.2 miles per second of velocity and bending its orbit back out toward Earth. Once scientists have finished examining the collected telemetry, the European Space Agency plans to publish further imagery of Earth and the Moon captured by the JANUS science instrument onboard Juice.
- April 2023: Juice launches from French Guiana aboard an Ariane 5 rocket.
- August 2024: Executes a lunar-Earth gravity assist.
- August 2025: Performs a flyby of Venus to gain velocity.
- September 28, 2026: Completes the second Earth flyby, gaining 3.5 km/s in speed.
- January 2029: Scheduled final Earth flyby to set up the final Jupiter transfer.
- July 2031: Planned arrival at Jupiter to begin 35 moon flybys.
Following the 2029 Earth encounter, which will put the probe on an intercept with Jupiter, Juice will complete its transit to the Jovian system and conduct 35 targeted flybys of Ganymede, Europa, and Callisto before entering orbit around Ganymede in 2034.