JUICE flies past Earth on its way to Jupiter’s icy moons
JUICE has once again passed close to Earth, using our planet for another gravity assist on its long journey to Jupiter. During the flyby, the spacecraft’s scientific instruments were switched on, including the RADEM radiation monitor, to which LIP contributes.
The JUICE (Jupiter Icy Moons Explorer) spacecraft, operated by the European Space Agency (ESA), carried out its second Earth flyby today, 28 September, as part of its long journey towards the Jupiter system. The spacecraft made its closest approach at 12:45 pm Lisbon time, passing around 8,640 km above our planet over the Indian Ocean.
The mission’s ultimate goal is to study Jupiter and three of its largest moons - Ganymede, Callisto and Europa. These moons are of particular scientific interest because they are thought to harbour oceans beneath their icy crusts, making them promising places to investigate conditions that could support life beyond Earth.
It may seem surprising for the spacecraft to return to Earth rather than simply continuing towards Jupiter. However, the manoeuvre is part of a complex series of gravity assists. By using the gravity of different celestial bodies, JUICE can gain speed and adjust its trajectory without using excessive amounts of fuel. This flyby deflected the spacecraft’s trajectory by around 20 degrees and increased its speed by approximately 3.5 km/s.
Before this latest Earth flyby, JUICE had already completed the historic lunar–Earth flyby in August 2024 - the first manoeuvre of its kind ever performed by a spacecraft - followed by a Venus flyby in August 2025.
This latest flyby also presented an additional challenge. Shortly before closest approach, during several hours between 27 and 28 September, JUICE passed through Earth’s shadow, receiving no sunlight and relying entirely on its batteries. The operations team therefore had to carefully prioritise the most important scientific observations during this period.
Unlike the Venus flyby, when extreme thermal conditions meant that most scientific instruments had to be switched off and the spacecraft’s high-gain antenna was used as a heat shield, this time all 10 of JUICE’s scientific instruments were switched on. Between 23 September and 3 October, the instruments are collecting data on Earth and the Moon, providing an important opportunity for calibration and preparation ahead of the mission’s main scientific phase at Jupiter.
The RADEM radiation monitor, to which LIP contributes, is also continuing to collect data, measuring the radiation environment around Earth. One particularly interesting aspect of this passage is that JUICE will spend several days travelling through the Earth’s magnetotail - a complex region formed by the interaction between Earth’s magnetic field and charged particles from the Sun. The flyby will provide valuable measurements of this dynamic region of near-Earth space.
The mission plan includes one final return to Earth in January 2029. From there, JUICE will continue towards the Jupiter system, where it is expected to arrive in July 2031, marking the beginning of the mission’s main scientific phase.
More information: JUICE to fly past Earth for third gravity assist — ESA