The main objective of the European mission Juice to the icy moons of Jupiter will be Ganymede, the largest of the planet’s satellites and a true natural laboratory for the study of the icy worlds of the Solar System. After eight years of travel, in fact, and despite the fact that the spacecraft will fly over Europa twice and Callisto another 21 times, the greatest research efforts of the European Space Agency (ESA) will not be carried out on either of these two moons.
But why Ganymede and not, for example, Europe itself, which at first seems the most promising? One good reason, no doubt, is that very soon, in 2024, NASA’s Clipper mission will reach the Jovian system and focus precisely on that enigmatic moon. Juice, therefore, will limit itself to providing a series of data on Europe that will facilitate this subsequent mission. Data, above all, on the presence of pools of liquid water on its surface and the possible columns of water vapor that emanate from its underground ocean and are launched into space.
Despite this, Juice is a unique mission, as it will be the first spacecraft to orbit a moon other than our own, and also the first to switch from a planet’s orbit to one of its moons. In fact, it will first orbit Jupiter, flying over Europa, Callisto and up to 12 times over Ganymede itself as it circles the gas giant. The spacecraft will then jump to Ganymede, around which it will stay for an entire year, and begin its in-depth study of that moon. To do this, it will come close to only 400 km from its surface.
Reasons to study Ganymede
As the ESA explains, there are “a good handful” of reasons why Juice will focus on Ganymede. The first is that scientists believe that a vast ocean of salt water lurks beneath its icy shell. One that could be large enough to engulf Ganymede entirely, though its composition and depth are not entirely clear.
For this reason, one of Juice’s main missions will be, precisely, to explore this large body of water and compare it with the available data from the subterranean oceans of other icy moons, and thus have a clearer image of how suitable these can be. worlds when it comes to harboring life.
But that is not the only reason. Ganymede, in fact, is the only moon (and one of the only three bodies in the Solar System) capable of generating its own magnetic field. On Earth, the magnetic field is created by the rotation of the liquid iron outer core around the solid core, but how does Ganymede do it? What drives its inner ‘dynamo’, and why don’t we see the same on other moons?
Ganymede’s magnetic field forms a small magnetosphere, which exists within the much larger magnetosphere of Jupiter itself. That little ‘magnetic bubble’ therefore constantly interacts with the powerful Jovian field, giving rise to powerful auroras. Juice will measure these magnetic fields, as well as surrounding particles, atoms, and molecules, and will study the processes taking place around the Jovian moon and how those processes relate to Jupiter itself, its radiation belts, and the other moons. . This is essential information to understand how these satellites that, in principle, are so promising for life, form and evolve around the gas giants.
A unique geology
Lastly, and in terms of its geology and evolution, Ganymede occupies a unique position in the Jovian system, which makes it a true ‘window’ open to study the history of the giant planet and its moons over thousands of years. of millions of years.
The complex surface of Ganymede, in fact, shows a great variety of ages and compositions, and is made up of both ancient and cratered terrain, such as those seen on Callisto, as well as new, smooth surfaces, such as those seen on in Europe. By studying the features of Ganymede’s varied surface, scientists will gain insight into how space impacts and geological processes, such as tectonics, have shaped Jupiter’s moons over time. Of course, Juice will also try to determine the physical properties of the moon’s icy shell, which is believed to be up to 130km thick and underlies the supposedly global underground ocean.
In short, Juice will study everything from Ganymede’s rotation to its gravity and geophysics, its shape and interior structure, its magnetic field and atmosphere, its composition and mineralogy, its icy crust and surface features, its emissions into space, its interactions with its environment and, more importantly, its underground ocean. It will also complete what will be the first ‘tomography’ of this Jovian moon, reconstructing a view of its interior and evaluating its biological signatures, that is, the elements that are considered biologically essential, although not sufficient, for life, such as carbon. , oxygen, magnesium, iron and liquid water.
To carry out these tasks, the spacecraft is equipped with 10 state-of-the-art scientific instruments, from optical cameras to infrared spectrometers, radars, laser altimeters, magnetometers…, as well as an experiment (PRIDE) and a radiation monitor. (RADEM). Taken together, Juice will paint a complete new picture of Ganymede and add a wealth of valuable data to what already exists about the enigmatic icy moons of our Solar System.