Shortly after taking off aboard an Ariane 5 rocket, at 12:14 GMT, the space probe separated from the launcher, 1,500 km above the Earth as planned.

The Ariane 5 mission "is a success," said Stéphane Israël, president of Arianespace, from the Guiana Space Center.

The emotion and relief were palpable, while Thursday the launch had to be postponed for 24 hours, due to the risk of thunderstorms.

"I was very stressed, it was a roller coaster!" said Josef Aschbacher, director general of the European Space Agency (ESA). "I am extremely proud for Europe because Juice is the biggest mission of the decade, and the most complex ever sent to Jupiter," he said.

Once the separation was successful, the teams still had to wait for the satellite to send its first signal, which it ended up doing after a few - long - minutes of suspense.

The probe of more than six tons was then able to deploy its huge solar panels, the size of a basketball court, another crucial step. "That's it, let's start!" said Olivier Witasse, ESA's Juice scientist.

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

"It will take another 17 days for the probe to deploy its antennas, and in three months we will have the final diagnosis on its performance. We will then be launched into the interplanetary travel phase," explains Nicolas Altobelli, in charge of the mission.

Eventful journey

The cruise of Juice (Jupiter Icy Moons Explorer) promises to be long and "not at all quiet," says Carole Larigauderie, head of the Juice project at the National Center for Space Studies (CNES).

Juice will reach its final destination in 2031, more than 600 million kilometers from Earth on average. Unable to reach Jupiter directly, the craft will have to go through complex gravitational assistance maneuvers that consist of using the force of attraction of other planets to gain speed.

The Ariane 5 rocket carrying the European space probe Juice takes off from Kourou, French Guiana, on April 14, 2023 © Jody AMIET / AFP

By a Moon-Earth flyby first, then of Venus (2025), then again of the Earth (2029), before taking its momentum towards the mastodon of the solar system and its largest moons, discovered by Galileo 400 years ago: Io the volcanic and its three icy companions Europa, Ganymede and Callisto.

This is the first time that space Europe has gone to explore a planet in the outer solar system, which starts after Mars.

"By small touches, space exploration pushes the frontiers of knowledge," Thomas Pesquet told AFP.

Designed by Airbus, Juice carries ten scientific instruments (optical camera, imaging spectrometer, radar, altimeter, magnetometer, etc.). Which will allow a better understanding of the Jovian system, considered as a "mini-solar system".

The Juice probe is presented to the press on January 20, 2023 in Toulouse, before its departure for Kourou in French Guiana © Charly TRIBALLEAU / AFP / Archives

"Worlds-ocean"

But the main quest is to find environments conducive to the appearance of life. If Jupiter, a gaseous planet, is uninhabitable, its moons Europa and Ganymede are ideal candidates called "ocean-worlds": under their ice surface, they shelter oceans of liquid water, and only water in the liquid state makes life possible.

Juice targets Ganymede: In 2034, it should be placed in orbit around this natural satellite, the largest in the solar system and the only one to have a magnetic field protecting it from radiation.

Trapped between two thick ice crusts, Ganymede's ocean is extremely deep. There would be "five or six times more liquid water on Ganymede than on Earth," decrypts Olivier Witasse.

The ocean of Jupiter's © moons Jonathan WALTER / AFP

Previous observations in orbit have suggested that this water would be salty, "but life on Earth started in saltwater oceans," adds the scientist.

The challenge for Juice is to know the composition of this ocean, in particular to know if an ecosystem could develop there.

"We know that on Earth, there is a subglacial lake (in Antarctica, editor's note) where we found a kind of mucus that develops - so life," says Carole Larigauderie.

"If Juice can prove that Ganymede is habitable so that he can go and check in the future that there is life, that would be fabulous!"

The launch of Juice, costing 1.6 billion euros, comes in the midst of the launcher crisis for Europe, virtually deprived of autonomous access to space after the departure of the Russian Soyuz rockets from Kourou, the cumulative delays of Ariane 6 and the failure of the first commercial flight of Vega C.

Friday's flight is the penultimate of Ariane 5 before the first of Ariane 6 scheduled for the end of 2023.

© 2023 AFP