Huge oceans of liquid water
move beneath its ice
, propitious grounds for the emergence of life.
The exploration of
Jupiter's icy moons
, the goal of the JUICE mission, opens a new chapter in the search for
other habitable worlds.
These environments are so far from the Sun that astronomers had long since excluded them from the zone considered habitable in the solar system, which "until recently
ended at Mars
," explains astrophysicist Athéna Coustenis, one of the scientific leaders of the European probe. .
On the surface of the moon Europa there are huge oceans of liquid water (Reuters).
But the discoveries made by the Galileo (1995) probes around Jupiter and Cassini (2004) around Saturn expanded the field of research.
It does not focus on these giant, gaseous planets, not conducive to life, but on their icy moons:
Europa and Ganymede
for Jupiter and
Enceladus and Titan
for Saturn.
The European Space Agency (ESA) JUICE mission (Jupiter Icy Moons Explorer, Explorer of the Icy Moons of Jupiter) will depart there this Thursday, which will focus especially on Ganymede, while NASA's next mission, Europa Clipper, will focus on Europe.
environment conducive to life
The main attraction of these satellites of the largest planet in the solar system are the oceans of liquid water that hide under their frozen surface, an
environment conducive to life.
"This is the first time that we are going to explore habitats beyond the ice line, where liquid water can no longer exist on the surface," explained Nicolas Altobelli, JUICE manager for ESA in January from the Airbus headquarters, which conceived the probe.
The probe must reach the orbit of Ganymede in 2034, the largest satellite in the solar system and also the only one that has its own magnetic field to protect it from radiation.
All these features suggest a stable environment, another condition for the emergence of life and its maintenance.
Jupiter is very far from the Sun (Nasa - AP).
"It is not a question of life appearing, but of its being maintained," says Athéna Coustenis, a researcher at the LESIA laboratory at the Paris Observatory.
Unlike missions to Mars, which search for the remains of life that has now disappeared, the exploration of the icy moons looks for
environments that are still habitable
, which is not the case on the red planet.
Habitability also requires a source of energy.
But in the freezing temperatures of Jupiter's environment, this does not come from the Sun but from the gravity that the huge planet exerts on its satellites, with "tidal effects" similar to those that occur on Earth with its moon.
This phenomenon makes it possible to "dissipate the heat inside the moons and keep the water in a liquid state," explains Francis Rocard, a planetologist at the National Center for Space Studies (CNES).
Jupiter's moon Ganymede and its halo of water (NASA).
The ocean of Ganymede is "gigantic"
, describes Carole Larigauderie, JUICE project manager at CNES.
Wedged between two thick layers of ice, it can be several tens of kilometers deep.
"On Earth, we have come to find life forms at the bottom of the abysses," he says.
Indeed, some terrestrial ecosystems are capable of maintaining themselves without light and are a hotbed of microorganisms such as bacteria and archaea.
This ecosystem needs nutrition to maintain itself.
"The question is whether the Ganymede ocean contains them," says Coustenis.
It would be necessary, for example, for the ocean to be able to absorb components deposited on its surface to dissolve them later in the water, develops astrophysics.
eight months orbiting
JUICE's instruments will survey this ocean from all sides to assess its depth, its distance from the surface and, they hope, composition as well.
The probe will orbit around the satellite for about eight months
and will be able to approach up to 200 km in height, sheltered from radiation.
Without this magnetosphere, its sister Europa is less hospitable to a spacecraft.
The American probe Europa Clipper, which will reach its destination at the same time as JUICE, will only be able to fly over it.
An artist's rendering of the possible "Great Lake" of the moon Europa (Britney Schmidt / Dead Pixel VFX / Univ. of Texas - Austin).
However, the data collected by the two missions will be complementary, the scientists note.
If Ganymede is shown to meet all the requirements to support life, "the next logical step" would be to send
a lander
, said Cyril Cavel, Airbus' chief scientist.
"This is part of the dream," although not yet part of the project at the moment, he added.
AFP Agency.
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