A space expedition leaves to explore the planet and three of its satellites, Callisto, Ganymede and Europa, likely to harbor life.
By Chloe Durand-Parenti
Space. The Juice probe is due to take off on April 13 towards Jupiter and three of its four largest moons – Ganymede, Callisto and Europa (from left to right) in order to unravel their mysteries.
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AT Kourou, in Guyana, the European space probe Juice (Jupiter Icy Moons Explorer), laden with scientific instruments, is biding its time. She is due to take off on April 13 to the planet Jupiter and three of its four largest moons: Ganymede, Callisto and Europa.
Never had the European Space Agency (ESA) and its partners – including the National Center for Space Studies (Cnes) – ventured into the exploration of bodies so far away: around 630 million kilometers from the Earth (around 1,630 times the Earth-Moon distance!). A prime objective because the Jovian system remains poorly understood. Only one mission has been devoted to it so far, that of the American Galileo probe launched in 1989, which suffered from technical difficulties that compromised part of its results. As for the American mission Juno, with Jupiter since 2016, it is only centered on the planet.
Oceans. Fascinatingly, Jupiter is the largest planet in the solar system and the archetype of the many gas giants discovered over the past thirty years around stars other than the Sun. Exoplanets too distant to be approached. But the Jovian system has other attractions too! It features a very complex invisible facet made up of magnetic fields that emanate, in part, from Jupiter itself and interact with its moons. Nothing comparable exists in our vicinity, if not the Sun itself! Enough to make it a natural laboratory to better understand electromagnetic phenomena. There is also its astonishing diversity: “While we thought it was so cold there that everything was inert, Galileo showed us that the moons of Jupiter were all different”, explains Olivier Grasset, researcher at the Planetology and Geosciences Laboratory at the University of Nantes (CNRS). Some present an old cratered surface like Ganymede, or even very old, long frozen like Callisto, or still young and smooth with probable geysers gushing at the South Pole like Europa. Better still, each of these three moons would hide, under its ice, an ocean capable of sheltering life.
Exception. How is it possible ? The tidal forces exerted by massive Jupiter warming these moons may not be the whole story. “For the search for life, the ocean of Europa has the greatest potential: it is believed that, as on Earth, liquid water is found there in direct contact with the rocky mantle of the moon”, notes the scientist. However, this mantle can provide the minerals necessary for a complex chemistry of the type that led to the appearance of life on Earth. On the other two moons, the configuration is different. “On Callisto, we are not sure that the moon has a well-differentiated internal structure. As for Ganymede, its ocean would be sandwiched between surface ice and a layer of high-pressure ice separating liquid water from the mantle. » Which makes it less fertile. But Ganymede has another rare characteristic, favorable to the living: it is, with the Earth, one of the rare solid bodies of the Solar System to have a magnetic field protecting it from cosmic particles. “Ganymede is the richest object. With its size close to that of Mars, its complex composition, its magnetic field and its ocean, it is a planet in itself. Studying its geological history is essential to understanding the formation of the Jupiter system, and even that of the solar system, in which the giant planet played an important role. » Ganymede could, moreover, constitute a typical model of certain icy worlds detected around other stars. This is why, after having focused on Jupiter’s atmosphere and magnetic environment, having flown over Europa twice, Callisto 21 times and Ganymede 12 times, Juice will end its mission in orbit around the latter in order to study in detail§
The particularities of Jupiter and its satellites
JUPITER. Diameter : 140,000 km. 11 times the size of Earth and 318 times its mass. Gas giant composed of approximately 86% hydrogen and 14% helium. Average surface temperature: – 145° C. Has at least 92 moons.
GANYMEDE. Diameter : 5,300 km – close to that of Mars (6,800 km). Curiosities: Its ocean, caught between two layers of ice; its own magnetic field; its composition and complex structure; its dawns.
CALLISTO. Diameter : 4,800 km. Curiosities: Its very old surface studded with craters makes it a vestige of the primitive Jovian system; its internal structure, of which we do not know if it is well differentiated; Geologically dead, Callisto would however hide a thin layer of liquid water.
EUROPE. Diameter : 3,100 km. Curiosities: Its young and active surface; the geysers spotted near its South Pole; its ocean, in direct contact with its rocky mantle, which is particularly favorable to the emergence of a complex chemistry likely to lead to life.
The instruments of the Juice probe
1.Majis, spectro-imagervisibleAndinfrared Characterization of Jupiter’s clouds, ices and minerals on the surface of the moons.
2.Gala,laseraltimetric Study of the deformations of Ganymede by the tides; study of the morphology and topography of Europa and Callisto.
3.SWI,instrumentTowavessubmillimeter Investigation of the structure, composition and dynamics of Jupiter’s atmosphere; study of the atmosphere and the surface of the moons.
4. PEP,detectorsofparticles Characterization of the Jovian environment.
5.3GM experience Study of gravity fields.
6. Pride Experience Accurate measurements of Juice’s position and velocity.
7.Radar Rime Sounding through the ice to determine the structure of the subsurface of the moons up to 9 km deep.
8. RPWI Instrument Measurement of radio and plasma waves.
9.J-MAG, magnetometer Study of the magnetic fields of Jupiter and Ganymede, detection of hidden oceans.
10. UVS, ultraviolet spectrometer Sounding of atmospheres, study of auroras.
11. Janus, cameraoptical
The stages of a very long journey
Prateek Sarpal © CC NC SA – NASA/JPL/DLR (x3) – SEBASTIAN KAULITZKI/Science Photo Library AFP/SPL