The European Space Agency’s Juice spacecraft swept past Earth on September 28 and left with about 7,830 miles per hour more speed than it arrived with. The pass took it 5,370 miles above the Indian Ocean, and the borrowed momentum bends its path by about 20 degrees toward Jupiter, where it is due in July 2031.
ESA confirms the same numbers in metric units: closest approach at 8,640 kilometers, a speed gain of 3.5 kilometers per second, and a deflection of 20 degrees from the pre-flyby path. Space.com gave the mph equivalent, about 7,830. The closest approach came at 11:45 UTC on September 28, 2026, or 13:45 Central European Summer Time.
A gravity assist that saves propellant
The maneuver was the third gravity assist of the trip, as Space.com’s account of the flyby counts them. A spacecraft cannot carry enough fuel to reach Jupiter directly, so mission designers route it past planets that hand over a little of their own orbital energy. Juice launched on April 14, 2023, aboard an Ariane 5 from Europe’s spaceport in French Guiana, and its mission plan lists four such maneuvers: a lunar-Earth flyby in August 2024, Venus in August 2025, this Earth pass, and a second Earth pass in January 2029.
Precision matters because the geometry is unforgiving. Angela Dietz, Juice’s Spacecraft Operations Manager, said in ESA’s report on the flyby that the flyby “required ultra-precise navigation in real time,” and that careful planning meant only a small amount of the propellant reserved for the flyby was used. Operators had six opportunities for trajectory correction in the four weeks beforehand and needed only one minor burn.
Whatever propellant was not spent stays on board. Dietz put the payoff plainly in the ESA report: the leftover propellant is extra to use at Jupiter for observations of the planet’s icy moons. The spacecraft’s route also carried it close enough to be seen from the ground, since ESA’s preview said amateur astronomers over Australia could spot it 15 to 30 minutes before closest approach.
Instruments tested on Earth and the Moon
ESA had described the pass in advance as a chance to calibrate the spacecraft’s 10 instruments on familiar targets. In its preview of the flyby, the agency noted that Earth’s shadow would cut off sunlight from 21:24 CEST on September 27 until 06:03 CEST on September 28, so Juice had to run on batteries alone through the approach. Claire Vallat, Juice Project Scientist, told Space.com that the simpler operational profile compared with the 2024 lunar-Earth flyby would let the team turn the spacecraft in all different directions to point its science instruments at different parts of Earth and the Moon.
The spacecraft then spent several days crossing Earth’s magnetotail, the stretched-out tail of the planet’s magnetic field, measuring magnetic fields and charged particles. ESA says the European-Chinese Smile mission watched auroras and magnetic activity near Earth’s poles at the same time, which lets researchers compare distant tail activity with what showed up overhead.
Pictures came too, though only a few so far. A monitoring camera, JMC1, a 1024 x 1024 pixel unit built to check the spacecraft’s booms and antennas rather than to take science images, captured Earth at 13:58 CEST as Juice moved away from closest approach. According to ESA’s image caption, the frame shows much of Africa, with Madagascar at left and parts of Yemen and Oman above the Gulf of Aden. Higher-resolution pictures are handled by the JANUS camera, and ESA says processed JANUS images and spectra are expected in the coming weeks.
What comes after the flyby
The remaining trip is long. Juice returns to Earth in January 2029 for the last assist before Jupiter, then arrives in July 2031, and eventually begins a series of 35 flybys of Jupiter’s moons Ganymede, Callisto, and Europa. It is scheduled to enter orbit around Ganymede in 2034, with Ganymede the primary target as both a planetary body and a potential habitat.
ESA’s mission page describes the goal as detailed observations of Jupiter and its three large ocean-bearing moons, and as a study of “the wider Jupiter system as an archetype for gas giants across the Universe.” Ten instruments ride on the spacecraft for that work, which is why the calibration passes over Earth and the Moon were scheduled around the battery-only stretch inside Earth’s shadow, with the tasks most relevant to Jupiter operations given priority.
One unanswered question is what the JANUS images will look like, since ESA has released only a monitoring-camera frame so far. For the mission itself, the figure to watch is the propellant margin Dietz described, which ESA has not quantified in public reports on the flyby.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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