Diagram of the conjunction of Jupiter and Saturn with their moons. / Federation of Astronomical Associations of Spain
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.
Source: AFP
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 the AFP. astrophysicist Athena Coustenisone of the scientific leaders of the European probe.
But the discoveries made by the probes Galileo (1995) about Jupiter and Cassini (2004) around Saturn expanded the field of investigation.
This one focuses not on these giant, gaseous planets, not conducive to life, but on their icy moons: Europa and Ganymede on Jupiter and Enceladus and Titan for Saturn.
The European Space Agency (ESA) JUICE (Jupiter Icy Moons Explorer, Explorer of the Icy Moons of Jupiter) mission will depart there on Thursday, which will focus especially on Ganymede, while NASA’s next mission, Europa Clipper, will focus on Europe.
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, head of JUICE for ESA in January from the Airbus headquarters, which conceived the probe.
The probe should reach the orbit of Ganymede in 2034the largest satellite in the solar system and also the only one that has its own magnetic field to protect it from radiation.
– Gigantic ocean –
All these features suggest a stable environment, another condition for the emergence of life and its maintenance.
“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 allows “to dissipate the heat inside the moons and keep the water in a liquid state,” he explains. Francis Rocard, planetologist at the National Center for Space Studies (CNES).
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.
– Complementary missions –
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.
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 spaceshiphe. The American probe Europa Clipper, which will reach its destination at the same time as JUICE, will only be able to fly over it.
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 this time, he added.
