Juice swings past Earth to boost its way toward Jupiter

ESA’s Juice just used Earth as a slingshot to Jupiter. On September 28, the spacecraft skimmed the upper atmosphere of the Indian Ocean, passing within 8,640 kilometers of the surface, and let Earth’s gravity bend its path toward the outer Solar System.

Juice’s path was altered by 20 degrees during the flyby, and its velocity increased by 3.5 kilometers per second, yet the maneuver consumed nearly no fuel.

The Slingshot That Saved Fuel

Juice’s Spacecraft Operations Manager, Angela Dietz, described the precision required. “The flyby required ultra-precise navigation in real time. Thanks to our very careful planning, we used only a small amount of the propellant reserved for this flyby,” she said.

“This gives us more to use at Jupiter to carry out observations of the planet’s icy moons.”

Before the spacecraft reached its target, the team held six windows for correcting its path. Of those six chances, they made use of just one.

Juice came under close scrutiny from controllers starting on August 17, with monitoring continuing through October 10. Its nearest approach occurred at 13:45 CEST (11:45 UTC).

Testing Instruments on Earth

The flyby was not just about changing direction. It also gave scientists a rare chance to test Juice’s 10 scientific instruments on a real planetary target.

This was the third such opportunity during the mission. The first came during Juice’s 2024 lunar-Earth gravity assist, followed by the spacecraft’s 2025 observations of Comet 3I/ATLAS.

For months, teams from ESA’s spacecraft operations, science operations and technical centers worked together with outside groups that manage the instruments. Their aim was to plan when each instrument could run and secure as much calibration time as possible from the spacecraft’s limited resources.

The Juice project scientist, Claire Vallat, guided the operation. She detailed the limits: “Given the limited time available and operational constraints, instrument activities sometimes have to be prioritized, for example when Juice was in Earth’s shadow this morning, and relying on battery power alone.” She added that during this flyby, calibration activities were chosen based on how much they would help prepare the instruments for their work at Jupiter, while also weighing whether an opportunity was one-of-a-kind or could be arranged later along the way.

Preparing for Jupiter’s Icy Moons

The Earth encounter was relatively simple compared to what awaits Juice. The spacecraft will carry out 35 flybys of Jupiter’s large moons Ganymede, Callisto and Europa.

Years before the first encounter, planning had already begun. Discussions about how instruments would operate during the Europa flybys started roughly 10 years ago and will keep going until Juice actually passes the moon in the early 2030s.

Our planet functions as a practice run for scientists to adjust their instruments, observe how they work in space, and improve the methods that will eventually process the information they collect.

The Magnetotail Passage

Juice also spent several days traveling through Earth’s magnetotail, the long extension of Earth’s magnetic field that stretches away from the Sun.

Juice got the chance to gauge magnetic fields and electrically charged particles at great distance from Earth. Meanwhile, the European-Chinese Smile mission has been watching the northern lights while measuring magnetic fields and particles near the planet.

Combining measurements from Juice and Smile could link activity deep in Earth’s magnetotail with events around the planet’s polar regions.

What Comes Next

Earth has not heard the last from Juice. The probe will make its third and final pass by our world in January 2029.

That encounter will put Juice on the final trajectory needed to reach Jupiter in 2031.

The Instruments to Watch

The expected outcomes include pictures of Earth and the Moon captured at high resolution by JANUS, Juice’s scientific camera. Once the data arrive on Earth and the instrument teams have evaluated them, scientists plan to release both the images and the spectra within the coming weeks.

The trip ahead for Juice is long, with a decade of close passes remaining. The flyby of Earth has already proven what the team can accomplish when every piece falls into place.

The operation worked as planned. The vehicle conserved its fuel, put its instruments through their paces, and secured a rare glimpse of Earth’s magnetic tail.

Source material: “ESA’s Juice just used Earth as a slingshot to Jupiter,” ScienceDaily.

astronomy · ESA · gravity assist · Juice · jupiter · spacecraft