The European Space Agency’s Jupiter Icy Moons Explorer is steering toward Earth for a close encounter on September 28, 2026, using the planet’s gravity to alter its speed and trajectory en route to Jupiter without burning excess fuel.
Spacecraft navigation is a game of celestial billiards, and few missions illustrate the principle quite like the Jupiter Icy Moons Explorer, known as Juice. Launched on April 2023, from Europe’s Spaceport in French Guiana aboard an Ariane 5 rocket, the 13,381-pound probe is winding its way through the inner solar system. Getting a heavy spacecraft to the outer solar system requires an unthinkable amount of propellant if attempted on a direct path. Instead, mission planners mapped out an intricate series of planetary flybys using Earth, the Moon, and Venus as gravitational stepping stones.
Trajectory Adjustments and the Third Earth Flyby
The upcoming encounter on September 28, 2026, marks the spacecraft’s third gravity assist and its second return to Earth. Flight controllers at the European Space Operations Centre in Darmstadt, Germany, scheduled the closest approach for 13:45 CEST over the Indian Ocean, where the probe will skim within 8,640 kilometers of the surface. This gravitational interaction will deflect the spacecraft’s trajectory by about 20 degrees and accelerate its velocity by roughly 3.5 km/s.
To ensure precision, the navigation campaign began on 17 August, establishing designated timeslots for trajectory corrections. Angela Dietz, Juice Spacecraft Operations Manager, noted the effectiveness of these adjustments (the agency’s operational update detailed the navigation milestones).
The encounter carries unique operational hurdles. Juice will pass through Earth’s shadow from the evening of September 27 into the morning of September 28, forcing the probe to operate entirely on battery power. To conserve energy, operators prioritized essential instrument observations while temporarily scaling back secondary systems.
A Proven Route Through the Inner Solar System
The 2026 flyby builds on a sequence of milestones that began shortly after launch. In August 2024, Juice executed the first-ever lunar-Earth double flyby. That maneuver served as a precise braking action, saving up to 150 kilograms of propellant to set up a subsequent visit to Venus.
A Venus flyby followed, adding significant velocity as the probe swung back toward Earth.
“All flybys are risky, requiring very careful planning and continuous monitoring. But the upcoming Earth flyby is much simpler from an operational perspective than the 2024 lunar-Earth flyby, where a flyby of the Moon set Juice up for a flyby of Earth the next day.”
Claire Vallat, Juice Project Scientist
Science Instruments and the Road to Jupiter
Just as it did during the 2024 lunar-Earth encounter, the mission turned its ten onboard science instruments on Earth and the Moon between September 23 and October 3. This active window allows instrument teams to calibrate sensors, analyze data collection tools, and test new techniques, such as using the navigation camera to track the Moon’s horizon (astronomical updates noted the testing phase). Researchers also gathered measurements of Earth’s magnetotail as the spacecraft drifted through the complex magnetic structure shaped by solar winds.
Project scientists emphasized the value of these calibrations.
“This is great news for science, because it means we will be able to turn Juice in all different directions to point its science instruments at different parts of Earth and the moon.”
Claire Vallat, Juice Project Scientist
Following Sunday’s acceleration, Juice will require one final Earth flyby in January 2029 (independent reporting confirmed the upcoming trajectory adjustments). That final alignment will deposit the spacecraft on its intercept course for Jupiter in July 2031, where it will conduct 35 flybys of the gas giant’s icy moons, probing hidden oceans and analyzing the magnetic field of Ganymede before entering orbit around Ganymede in 2034.
