In the clean room of its manufacturer Airbus, in Toulouse, the JUICE satellite (JUpiter ICy moons Explorer mission) lives its last moments on Earth.

Emotion overwhelms the team of engineers, technicians and scientists who have worked for many years on this flagship mission of the European Space Agency (ESA).

White coats and protective charlotte on the head, they can finally reveal to the press their "beast" of 6.2 tons, its 10 scientific instruments, its antenna 2.50 meters in diameter and its huge solar panels that it takes test one last time.

In a few days, the spacecraft will be placed, wings folded, in its transport container, before flying to Kourou in French Guiana, from where it will be launched in April by an Ariane 5 rocket.

As a farewell, a commemorative plaque has been engraved on the back in tribute to Galileo, the first to observe Jupiter and its largest moons, in 1610.

The volcanic Io and its three frozen companions Europa, Ganymede and Callisto, were "the first moons discovered outside our own", explains Cyril Cavel, JUICE project manager at Airbus Defense and Space, proudly showing a copy of "Sidereus nuncius". ("the messenger of the stars" in French) by the Italian astronomer - the first treatise on astronomy in history.

An extract from Galileo's book "Sidereus nuncius" was engraved behind the satellite, then covered with thermal insulation © Charly TRIBALLEAU / AFP

Earth and Venus as catapults

Four hundred years later, man is preparing to explore the gas giant's natural satellites in depth, by placing a probe in orbit around one of them for the first time.

JUICE will also be the first European mission to venture into the outer solar system - which starts after Mars, the last terrestrial planet.

We will have to wait because the journey promises to be long, with an arrival scheduled for 2031. And winding, since it is not possible to reach Jupiter, located 740 million kilometers from the Sun, by a direct trajectory.

Once launched, JUICE will have to use the gravitational assistance of the Earth, then go to seek that of Venus.

"It's like a catapult that gives us momentum to Jupiter," explains Nicolas Altobelli, scientific manager of the mission for the European Space Agency (ESA).

Its 85 m2 solar panels will also have to garner maximum power before going to face temperatures close to absolute zero (around -220 degrees).

The satellite is covered with thermal insulation blankets, to face extreme temperatures © Charly TRIBALLEAU / AFP

Once there, the vessel and its 2 billion kilometers on the clock will have to fit into Jupiter's orbit... after braking in total autonomy.

"If the maneuver fails, the mission is lost", explains Cyril Cavel.

Ganymede objective

JUICE will survey the Jovian system, fly over its moons, then orbit the larger Ganymede.

Its cameras, sensors, spectrometers and radars will try to understand if it meets the conditions conducive to life.

Not on the frozen surface, but 10 or 15 kilometers below, where liquid oceans move.

An environment potentially favorable to primitive life forms in deep habitats, such as bacteria - "we are not going to detect large fish", underlined the boss of the ESA Josef Aschbacher.

Several conditions must be met, including liquid water and a source of energy, in this case that of the "tidal effects" that Jupiter's gravity exerts on its moons.

Thanks to Ganymede's magnetic signals, JUICE could determine if water is in contact with a rocky core, which would allow chemical elements necessary for life, such as nutrients, "to be dissolved in the water", analyzes Nicholas Altobelli.

The Juice probe, explorer of the icy moons of Jupiter © Paz PIZARRO / AFP

The American probe Europa Clipper will complete the quest by exploring Europe.

If the two moons prove to be good candidates for life, the "logical next step" will be to send a lander there.

"It's part of the dream of scientists", says Cyril Cavel, "moved" to know that JUICE "will end its life on the surface of Ganymede".

© 2023 AFP