Juice is skimming Earth again—and borrowing its speed for Jupiter
ESA’s Juice spacecraft will pass 8,640 kilometres above Earth on September 28, using the planet’s gravity to bend its route toward Jupiter while its instruments rehearse the science they will do there.
A close pass with a long-term payoff
ESA’s Jupiter Icy Moons Explorer (Juice) is due to reach its closest point over the Indian Ocean at 11:45 UTC on September 28, passing 8,640 kilometres from Earth. The encounter is not a detour: Earth’s gravity will deflect the spacecraft’s trajectory by about 20 degrees and add roughly 3.5 kilometres per second to its speed. esa
That exchange lets mission controllers save propellant for the difficult work ahead. Juice launched in April 2023 and has already used a first-ever lunar–Earth flyby and a 2025 Venus flyby to reshape its orbit. A final Earth flyby in January 2029 will set up its arrival at Jupiter in July 2031. esa +1
Gravity does the heavy lifting
A direct flight to the outer Solar System would require far more launch energy and onboard fuel. Instead, the spacecraft repeatedly trades speed and direction with planetary motion: the Moon and Earth first slowed and redirected it, Venus then accelerated it, and this Earth encounter will tune the next leg. The method leaves more fuel for orbit insertion at Jupiter and, later, Ganymede. scientificamerican +1
The geometry is exacting. Flight controllers began a navigation campaign in August, with correction opportunities reserved for small errors. The spacecraft will also spend about nine hours in Earth’s shadow before closest approach, running on batteries while the team limits its power demands. esa +1
A rehearsal for ocean worlds
The flyby is also a science run, not just a propulsion trick. Juice’s 10 instruments will observe Earth and the Moon from September 23 through October 3, including several days sampling Earth’s magnetotail—the elongated magnetic region formed as the solar wind flows past the planet. esa +1
Its navigation camera will image the Moon’s horizon to test optical-navigation methods, while two monitoring cameras will record the passage. Those observations give teams a nearby target on which to calibrate instruments and analysis procedures before Juice studies Jupiter and its three large icy moons—Europa, Callisto and Ganymede. science +1
The destination is still years away
NASA describes Juice as an ESA-led mission built to investigate Jupiter’s system and those three moons, which may contain subsurface oceans. After arrival, the spacecraft is planned to make 35 moon flybys before entering orbit around Ganymede. science +1
The immediate test is simpler but unforgiving: the spacecraft must hit the right angle and velocity while emerging from Earth’s shadow. ESA says images from the flyby will be shared after the spacecraft sends them down; the next major navigation milestone is the 2029 Earth encounter. esa +1