JUICE launches to Jupiter's icy moons

On the morning of 14 April 2023, under a heavy Guianese sky, Europe's biggest planetary mission left Earth on the second-to-last Ariane 5 ever to fly. The day before, lightning risk had stopped the countdown minutes from launch; now the rocket punched through the clouds above Kourou at 09:14 local time carrying the Jupiter Icy Moons Explorer, Juice, a six-tonne robotic emissary bound for worlds where vast oceans hide beneath kilometres of ice. Some twenty-seven minutes after liftoff the spacecraft separated, and within the hour its signal reached home: Europe was on its way to Jupiter.

Juice is built for an environment that punishes spacecraft. At Jupiter, sunlight is roughly 25 times weaker than at Earth, so the probe spreads 85 square metres of solar array, among the largest ever sent into deep space. Its eight-year route is a masterpiece of celestial billiards: in August 2024 it performed the world's first lunar-Earth double flyby, skimming the Moon and then Earth a day apart, with a Venus flyby and further Earth passes to follow before arrival in July 2031. Ten instruments will then dissect Ganymede, Europa and Callisto across 35 close flybys.

The cruise nearly began with heartbreak. Weeks after launch, the 16-metre antenna of RIME, the ice-penetrating radar meant to sound the moons' hidden oceans, jammed against a stuck pin only millimetres across. For a month, controllers shook the spacecraft with its thrusters and rolled it to warm the mount in sunlight. On 12 May 2023 they fired a mechanical actuator inside the bracket; the jolt shifted the pin and the antenna sprang open. The mission's grandest ambition survived: around 2034, Juice is to settle into orbit around Ganymede, the first spacecraft ever to orbit the moon of another planet.