ESA's Jupiter Icy Moons Explorer, known as Juice, swept within 8,640 kilometers of Earth on September 28, using the planet's gravity to bend its trajectory by about 20 degrees and add roughly 3.5 kilometers per second to its speed, the European Space Agency said. The maneuver was the third of four gravity assists the spacecraft needs before it can reach Jupiter.
Mission controllers at the European Space Operations Centre in Darmstadt tracked the flyby closely, with closest approach occurring over the Indian Ocean at 13:45 CEST. In its mission update, ESA said flight teams used only one of six scheduled trajectory-correction opportunities in the month before the encounter, a sign of how precisely the approach had been planned.
"The flyby required ultra-precise navigation in real time," said Angela Dietz, Juice's spacecraft operations manager. "Thanks to our very careful planning, we used only a small amount of the propellant reserved for this flyby."
Why the long way round
Juice launched in April 2023 aboard an Ariane 5 rocket that lacked the power to send the roughly six-tonne spacecraft directly to Jupiter, some 800 million kilometers away. Instead, mission designers built a route using gravity assists, a technique that borrows a small amount of a planet's orbital momentum to reshape a spacecraft's path without burning extra fuel. The Juice mission has already completed a lunar-Earth flyby in 2024 and a pass of Venus in 2025; a final Earth flyby is scheduled for January 2029 before the spacecraft threads onto its approach to Jupiter, with arrival expected in July 2031.
The September encounter also doubled as a rehearsal for science operations. Juice project scientist Claire Vallat said the team prioritized calibration activities "based on their relevance to preparing the instruments for their work at Jupiter," testing some of the ten instruments Juice will eventually train on Ganymede, Europa and Callisto — three moons suspected of harboring vast oceans beneath their icy crusts.
Ganymede, the largest moon in the solar system, is Juice's primary target; the spacecraft is expected to become the first to orbit a moon other than our own when it settles into orbit around Ganymede in 2034. NASA's separate Europa Clipper mission, launched in 2024 and on a faster trajectory, is pursuing similar questions about Europa's ice-covered ocean and is due to arrive at Jupiter in 2030, a year ahead of Juice.
Monitoring-camera images captured during the September flyby, showing Africa and Madagascar from roughly 8,600 kilometers away, were released within hours of closest approach. ESA said Juice is now coasting toward its next milestone, a final Earth gravity assist in January 2029.
