Space probe whips around Earth as it gathers speed for Jupiter

A year after it left Earth on an epic eight-year journey to explore the moons of Jupiter, the Juice spacecraft is back where it started.
On Monday and Tuesday the European Space Agency’s probe will whizz 430 miles above a far more familiar moon — our own. Then, it will pass 4,300 miles above the Earth, from where it launched in April 2023, in the first ever “double gravity assist”.
While geographically it is no closer to its destination, the manoeuvre is a crucial step on its circuitous route to the solar system’s largest planet as it saves fuel by exploiting the gravitational pull of Earth.
It is also the first time that a probe has taken advantage of both the moon and the Earth in this way. Getting the path right, and then making the fine adjustments to keep it on course, is far from routine, Ignacio Tanco, the project’s spacecraft operations manager, said. “It’s like passing through a very narrow corridor, very, very quickly: pushing the accelerator to the maximum when the margin at the side of the road is just millimetres,” he said.
The European Space Agency (Esa) hopes that when Juice begins the scientific phase of its mission in 2031 it will give us a better understanding of Jupiter’s many moons, and three in particular: Ganymede, Europa and Callisto. Beneath their icy crusts, scientists believe there are liquid water oceans. Potentially, these could be habitable.
Using ten different instruments, including radar and lasers, the team at Esa want to conduct the most in-depth study of these moons ever, to better understand them both geophysically and, perhaps, as biological habitats. An instrument designed by a team involving UK scientists from UCL will sample particles ejected by the moons, potentially including from water plumes on Europa.
But first they have to get there. This week’s pass of the Earth is designed to change the craft’s course, and actually brake it slightly. This will put it in the correct position to pass Venus next year, and then the Earth two more times — in 2026 and 2029.
With each of these subsequent catapults, it steals a bit of momentum from the planets, giving it the energy to reach Jupiter. While it is possible to go there directly, the fuel required for both accelerating and braking would make the cost prohibitive. Just getting into position for this week’s pass used up almost 10 per cent of the craft’s fuel.
During the flyby, engineers at Esa will be able to test its instruments and take photographs. During its closest approach, at about 11pm (BST) on Tuesday, it might also be visible using binoculars to satellite-watchers on Earth.
Anyone hoping to wave it off on the next leg of its journey, however, will need to be in southeast Asia or the Pacific. Britons, unfortunately, will be on the wrong side of the planet.