ESA's Juice spacecraft sweeps past Earth on its way to Jupiter

A critical course correction

The European Space Agency’s Juice spacecraft has successfully swept past Earth, using our planet's gravity to bend its trajectory towards Jupiter while conserving vital fuel.

At 13:45 CEST (11:45 UTC) on 28 September, the probe made its closest approach, skimming 8,640 kilometres above the Indian Ocean. The carefully plotted gravity assist changed the spacecraft's direction by 20 degrees and increased its speed by 3.5 kilometres per second.

Because of meticulous planning in the weeks leading up to the encounter, mission controllers needed to make only one minor course correction out of six potential opportunities. This allowed the spacecraft to use much less fuel than anticipated.

"The flyby required ultra-precise navigation in real time," said Angela Dietz, the spacecraft operations manager for Juice. Dietz added that saving propellant now leaves more fuel for observations once the spacecraft reaches its destination.

Rehearsing for Jupiter's moons

The encounter also offered a rare chance to test Juice’s 10 scientific instruments on a real planetary target. Scientists spent months planning how to share the spacecraft's limited resources during the brief flyby.

For part of the pass, Juice was operating on battery power alone while in Earth's shadow. Claire Vallat, the project scientist, said that calibration activities had to be prioritised based on what would best prepare the instruments for their eventual work at Jupiter.

Scientists also used the opportunity to collect active space science. Juice spent several days travelling through Earth’s magnetotail—the stretched-out pocket of our magnetic field that points away from the Sun. Its measurements of magnetic fields and charged particles will be compared with data from the joint European-Chinese Smile mission, which was simultaneously observing the northern lights from closer to Earth.

What happens next

The public will get its first look at the results soon. ESA expects to release images and spectra in the coming weeks, including high-resolution shots of Earth and the Moon taken by Juice's scientific camera, JANUS.

Juice is currently on an eight-year journey to the outer solar system, having launched on an Ariane 5 rocket in April 2023. It has already used a lunar-Earth gravity assist in 2024 and observed Comet 3I/ATLAS in 2025 to help refine its systems.

The spacecraft will return to Earth one final time in January 2029 for another gravity assist, which will set its course for a 2031 arrival at Jupiter. Once there, it will perform 35 close passes of the icy moons Ganymede, Callisto, and Europa to study whether their subsurface oceans could support life.