Juno captured this view of the northern Ganymede regions on December 26, 2019. Annotations are added and the thick white line is 0 degrees longitude.
NASA / JPL-Caltech / SwRI / ASI / INAF / JIRAM
Jupiter has a lot of moons but one in particular reigns supreme: Ganymede. The largest Jovian moon is larger than Mercury and Pluto and has its own magnetic field. It’s an unusual world, with an inner ocean, an incredibly thin atmosphere, and an icy shell, and has fascinated astronomers since Galileo first discovered it in 1610.
Galileo’s discovery was monumental, but he did not have the tools at his disposal to really examine the moon. But 410 years later, NASA does. On December 26, 2019, the Jovian Infrared Auroral Mapper (JIRAM) in NASA Juno spacecraft He took the first images of the moon’s icy north pole, mapping the region for the first time.
The images show that there is an unusual form of ice on the pole, a type that we did not find on Earth, because the magnetic field filters particles from the sun, plasma, towards it. Without a decent atmosphere, it’s basically raining plasma on Ganymede’s ice.
“The JIRAM data shows that the ice in and around the north pole of Ganymede has been modified by plasma precipitation,” Alessandro Mura, Juno co-researcher at the National Institute of Astrophysics in Rome, said in a NASA statement. .
“It is a phenomenon that we have been able to learn for the first time with Juno because we can see the North Pole in its entirety.”
Plasma prevents ice from taking over the structure that we are used to seeing on Earth. When the water freezes here, it forms a crystalline structure: layer after layer of water molecules form a network of hexagonal rings. At the Ganymede poles, the ice takes an amorphous shape. Its molecular structure is disordered; there is no lattice, there are no rings. Analyzing and understanding these structures will provide further clues to the formation of Jupiter’s moons and the forces at play during their evolution.
And Juno should receive help in the next decade. The European Space Agency will seek to explore Ganymede when it launches JUICE, the Jupiter Icy Moons Explorer spacecraft in 2022. By 2029, it will arrive at Jupiter and should start doing close-up science on Ganymede around 2032. NASA will explore another interesting Jupiter Moon around the same time with the Europa Clipper, an orbiting spacecraft established in study a moon that could harbor microbial life.
