The European Space Agency’s Jupiter Icy Moons Explorer (Juice) will make a planned close pass of Earth on 28 September 2026, using the planet’s gravity to change course and gain speed on its way to Jupiter.
What will happen on 28 September
Flight controllers will guide Juice to a closest approach of approximately 8,640 km above Earth’s surface. That encounter is expected to deflect the spacecraft’s trajectory by about 20 degrees and increase its velocity by about 3.5 km/s. The nearest point will lie over the Indian Ocean at 13:45 CEST (11:45 UTC).
According to mission information, Juice will pass over Australia between 15 and 30 minutes before closest approach, travelling from the north‑east to the north‑west of the continent. Observers with sufficiently powerful binoculars or telescopes may be able to track the spacecraft during parts of that transit.
Why Juice needs multiple planetary assists
Reaching the outer Solar System requires either vast quantities of fuel or clever use of gravity. Juice launched in April 2023 from Europe’s Spaceport in French Guiana and has already used several gravity assists: a lunar–Earth manoeuvre described as a braking shortcut, followed by a Venus flyby that altered its path and added speed.
Rather than carry an impractical amount of propellant to fly directly to Jupiter and then slow down enough to be captured, mission planners have designed a sequence of planetary flybys. The 28 September Earth pass is the third in this series; a final Earth flyby is scheduled for January 2029. Those assists together place Juice on the optimal path to intercept Jupiter in July 2031.
What a gravity assist does
A gravity assist, or slingshot manoeuvre, uses a planet’s motion and gravitational field to alter a spacecraft’s velocity vector. The spacecraft effectively steals a tiny amount of orbital momentum from the planet, changing its direction and speed without burning large amounts of fuel. For Juice, the September pass will both bend its trajectory and boost forward speed by several kilometres per second — the equivalent of a large propulsive manoeuvre achieved for free.
- Launch: April 2023
- This flyby: 28 September 2026, closest approach ~8,640 km
- Delta in trajectory: ~20° deflection
- Delta-v: ~3.5 km/s speed increase
- Final Earth assist: January 2029
- Planned Jupiter arrival: July 2031
Using gravity assists is a well‑established method in deep‑space missions, allowing agencies to reach distant targets with spacecraft that are smaller and less costly than a direct‑transfer approach would require.
Visibility and public interest
The mission page notes that amateur astronomers equipped with the right optics may be able to follow Juice during parts of its pass, and trajectory data are publicly available for those who want to attempt a sighting. The flyby also offers routine opportunities for ground teams to check spacecraft systems and make small adjustments while Juice benefits from the gravitational interaction.
| Event | Date/time | Key figure |
|---|---|---|
| Closest approach | 28 September 2026, 13:45 CEST (11:45 UTC) | ~8,640 km |
| Velocity change | During flyby | ~3.5 km/s |
| Trajectory deflection | During flyby | ~20° |
| Final Earth assist | January 2029 | Prepares for Jupiter intercept |
| Jupiter arrival | July 2031 | Target |
Juice’s ultimate goal is to study Jupiter’s icy moons — Europa, Ganymede and Callisto — which are considered among the most promising places in the Solar System to seek environments that might support life. The current sequence of planetary assists keeps the mission feasible with the propulsion and mass constraints set at launch.
As with any interplanetary mission, the schedule is precise but subject to the demands of orbital mechanics and the health of the spacecraft. Flight controllers will monitor systems closely during the encounter and issue updates as they confirm telemetry and trajectory outcomes.
