The exploration of the icy moons of Jupiter by the " Juice " space probe launched by the European Space Agency Thursday from the Kourou base in French Guiana constitutes a new stage in the search for habitable worlds outside the planet, as their ice caps hide vast oceans of water beneath them. The liquid is supposed to provide a fertile environment for life forms.

These environments are so far from the sun that astronomers have long excluded them from the region of the solar system considered habitable, "which until recently stopped at Mars," astrophysicist Athena Kostinis, who is among the science officials, told AFP. for the European probe.

The explorations of the Galileo probes (1995), which targeted Jupiter, and Cassini (2004), which orbited Saturn, pushed the boundaries of research that focused not on these gas giant planets, which are characterized as being inhospitable to life, but on their icy moons, Europa and Ganymede. for Jupiter and Enceladus and Titan for Saturn.

These moons are characterized by the presence of vast oceans of liquid water under their icy surface, knowing that water in its liquid form alone makes life possible on the surface of any celestial body.

"This is the first time that we will explore possible habitable places beyond the frost line," says Nicolas Altobelli, responsible for the "Goss" probe from the European Space Agency, in an interview dating back to January made in Toulouse by the "Airbus" company that designed the probe. It is not possible to record the presence of liquid water on the surface of a planet or moon.

The next NASA mission, called Europa Clipper, will target Europe. As for the probe, "Joss", it will focus on Ganymede. Joss is scheduled to enter the orbit of this moon in 2034, which is the largest moon in the solar system and the only one that has its own magnetic field that protects it from radiation.

There are many characteristics that indicate the existence of a stable environment, which is another condition for the emergence and continuity of life forms, because “what matters is not only that the place is habitable, but that life is viable,” as Athena Costinis asserts.

And unlike space missions to Mars that seek traces of ancient, vanished life, the underlying goal of exploring icy moons is to search for environments that are still habitable, which Mars does not demonstrate.

Another requirement for the possibility of life to exist is the availability of an energy source. In the freezing temperatures of the Jupiter system, the energy source is not the sun but the gravity that Jupiter exerts on its moons and causes "tidal effects" similar to what happens on Earth with the moon.

And the planetary scientist at the French Center for Space Studies, Francis Rocard, says that this phenomenon leads to "the dissipation of heat inside the moons and the preservation of the liquid form of water."

The head of the "Goss" project at the French Center for Space Studies, Carole Larigaudry, describes Ganymede's ocean as "huge". The depth between two thick layers of ice may be tens of kilometers.

"On planet Earth, we get to discover forms of life at the bottom of the abyss," she says. Some terrestrial ecosystems show the ability to continue without light, while teeming with microorganisms such as bacteria and archaea.

And such a system needs nutrients to keep going. "The issue is whether Ganymede's ocean contains similar elements," says Athena Kosthenis.

For example, the ocean must be able to absorb components deposited on the surface to then dissolve in the water, says the astrophysicist.

GOSS tools will explore this ocean with its various layers to measure its depth, its distance from the surface, and its composition, if available.
The probe will orbit Ganymede for eight months and may approach it up to an altitude of 200 km.

Because it does not have a magnetic field, Europa is less suitable for a spacecraft, and the American probe, Europa Clipper, which will arrive at its destination at the same time as Goose, will only be able to fly over its target. However, the data that the two missions will provide will be complementary, according to the scientists.

"If it turns out that Ganymede has indications of life forms, the next logical step would be to send a lander to it," said Cyril Cavill, scientific director at Airbus, adding, "It would be like a dream," although there are no plans at this stage. .