A gravitational slingshot with a scientific twist
On 28 September 2026, the European Space Agency's JUICE spacecraft — short for Jupiter Icy Moons Explorer — completed its penultimate gravity assist manoeuvre, swinging past Earth on its way to the outer solar system. Gravity assists are a cornerstone of deep-space mission design: by flying close to a planet, a spacecraft can borrow energy from its gravitational field, altering both speed and direction without burning a drop of propellant. For JUICE, these carefully choreographed encounters are the backbone of a journey expected to culminate at Jupiter in 2031.
The spacecraft lifted off in April 2023 aboard an Ariane 5 rocket from Europe's spaceport in Kourou, French Guiana. Since then, it has already completed flybys of the Moon and Venus as part of a multi-year interplanetary cruise. The Earth encounter marks the second-to-last such manoeuvre before a final gravitational boost sends JUICE on a direct course for the Jovian system.
Earth as a stand-in for Jupiter's moons
What set this flyby apart from purely navigational passes was the depth of scientific activity it enabled. With Earth serving as a well-characterised reference environment, ESA's mission teams seized the opportunity to put all ten of JUICE's scientific instruments through their paces under realistic operating conditions.
The instrument suite was designed to investigate three of Jupiter's largest moons — Europa, Ganymède and Callisto — which are thought to harbour vast liquid-water oceans beneath their frozen crusts. These subsurface oceans make them compelling targets in the search for environments that could, in principle, support life. During the Earth flyby, the sensors turned their attention to our planet's oceans, cloud cover and magnetic field: features that offer useful analogues to what the probe will encounter around Jupiter.
Beyond instrument calibration, the teams also rehearsed pointing procedures, data downlink protocols and cross-team coordination across multiple European ground stations. Running through these operational sequences while the spacecraft is still relatively close to home is essential for catching potential issues before JUICE is hundreds of millions of kilometres away and largely beyond reach.
Final approach to the giant planet
With the Earth flyby behind it, JUICE is now on the final leg of its cruise phase. One more gravity assist remains before the spacecraft commits to its Jupiter trajectory. Arrival at the giant planet is expected in 2031, at which point JUICE will begin an extensive tour of the Jovian system, conducting repeated close flybys of the icy moons before eventually settling into orbit around Ganymede — a milestone that would mark the first time a spacecraft has orbited any moon other than Earth's own.
The mission is designed to run for several years, gathering data that could reshape our understanding of how gas giant systems form and what conditions are needed for life to take hold elsewhere in the universe. For now, the September flyby has delivered a clear and practical result: JUICE's instruments are working as intended, its teams are coordinated, and the long wait for Jupiter is one step shorter.
