A spacecraft the size of a double-decker bus will pass within a few thousand kilometres of Earth on September 30, 2026 — and most people on the planet won't even know it's happening. That spacecraft is JUICE (JUpiter ICy moons Explorer), built by the European Space Agency, and what looks like a near-miss is really a precisely engineered slingshot. JUICE is using Earth itself as a free fuel stop on its eight-year journey to Jupiter.
What Is JUICE and Where Is It Going?
JUICE launched on April 14, 2023, aboard an Ariane 5 rocket from Kourou, French Guiana. Its destination is the Jupiter system, where it will study three of the gas giant's icy moons — Ganymede, Callisto, and Europa — all of which are thought to harbour vast liquid-water oceans beneath their frozen surfaces. According to Space.com, JUICE will be the first spacecraft ever to orbit a moon other than Earth's own, eventually settling into orbit around Ganymede, and it is scheduled to arrive at Jupiter in July 2031.
The core scientific question driving the entire mission is whether those subsurface oceans could support life. JUICE carries ten scientific instruments — radars, spectrometers, magnetometers, and cameras — to probe the moons' interiors and surfaces from orbit.
Why Does a Jupiter-Bound Probe Keep Swinging Past Earth?
This is where physics gets interesting. To travel directly from Earth to Jupiter, a spacecraft would need to leave our planet at around 11 kilometres per second. JUICE weighs almost 6,000 kilograms — making it one of the heaviest interplanetary spacecraft ever launched — and its Ariane 5 rocket could only push it to an escape velocity of 2.5 km/s. ESA explains that the mission uses a series of gravity-assist manoeuvres — essentially borrowing gravitational energy from planets it flies past — to make up the difference without burning enormous amounts of fuel.
JUICE's rocket gave it 2.5 km/s. Jupiter needs 11 km/s. Earth and its neighbours are providing the rest, for free.
A gravity assist works like this: as JUICE approaches a planet, the planet's gravity accelerates it; as it swings around and pulls away, the geometry of the manoeuvre means JUICE leaves faster than it arrived, relative to the Sun. No fuel burned. The planet loses an immeasurably tiny amount of orbital energy. JUICE gains the equivalent of a rocket burn.
The Flyby Sequence: How JUICE Got Here
The September 30, 2026 flyby is the third planetary close approach in JUICE's journey, and the second time it passes Earth alone. Here is the full sequence so far:
- August 19–20, 2024: The world's first-ever lunar-Earth double flyby. JUICE swung past the Moon at 21:16 UTC on August 19, then past Earth just over 24 hours later, flying just 6,840 km above Southeast Asia and the Pacific Ocean. No spacecraft had ever used the Moon and Earth as a combined gravitational lever in the same manoeuvre before.
- August 31, 2025: A Venus flyby, which bent JUICE's solar orbit and flung it back outward toward Earth, building on the speed gained from the lunar-Earth encounter.
- September 30, 2026: This Earth flyby — the one coming up. After this pass, ESA confirms JUICE will have reached the Jupiter transfer velocity of 11 km/s it needs to make the outer Solar System crossing.
One more Earth flyby remains — scheduled for January 2029 — before JUICE finally heads outward to Jupiter for its July 2031 arrival.
What Actually Happens on September 30 — and Can You See It?
Seeing JUICE with the naked eye is unlikely — the spacecraft is small, dark, and moving fast. Even during the August 2024 flyby, visual sightings required dedicated telescope setups. The event is less about spectacle and more about precision engineering: ESA's flight control team at ESOC in Darmstadt, Germany, will monitor the closest approach in real time, confirming that JUICE has threaded the exact gravitational corridor it needs. During the previous Earth pass, JUICE fired up eight of its ten onboard science instruments and photographed Earth and the Moon — expect similar data collection this time round.
ESA typically streams live commentary through its website and social media channels during major JUICE milestones. Keep an eye on the ESA JUICE mission page for confirmed timing as the date approaches. Track the countdown to the flyby on WatchIsUp so you know exactly when to tune in.
What Comes Next After September 30
After this flyby, JUICE will be travelling at the velocity it needs. It will arc onward for one final Earth gravity assist in January 2029, then make the long crossing to Jupiter. Once there, it will conduct flybys of Callisto and Europa before entering permanent orbit around Ganymede — the first time any spacecraft has orbited a moon other than our own.
If you enjoy tracking deep-space milestones, several others are coming up soon. The Solar Orbiter Venus Flyby is set for December 24, 2026, and NASA's Europa Clipper Earth Flyby follows on December 31, 2026 — a probe headed to Europa, the very moon JUICE will also study up close. The two missions will ultimately be working the same Jovian neighbourhood from different angles.
Sources
- Jupiter spacecraft completes first moon-Earth flyby, ESA says - CBS News
- ESA - Juice rerouted to Venus in world’s first lunar-Earth flyby
- JUICE (Jupiter Icy Moons Explorer) - eoPortal
- ESA - Juice’s lunar-Earth flyby: all you need to know
- JUICE — A complete guide to Jupiter's icy moon exploring mission | Space
- Jupiter Icy Moons Explorer
- ESA's JUICE spacecraft flies by Venus on its way to Jupiter's icy moons | Space
- JUICE - NASA Science