NASA’s Juno is studying Jupiter like no other mission before, peering through its cloud layers and delivering breathtaking images of the planet. Now it has returned the first images of Ganymede’s north pole.
Ganymede is not only the largest moon in the Solar System, but it is also the only one with its own magnetic field and a sub-surface ocean (like fellow Galilean moon, Europa) with more water than all of Earth’s surface water combined.
The interaction between its surface ice and magnetic field was one of the reasons NASA chose to conduct these observations. Plasma from Jupiter’s enormous magnetic field travels to the moon, whereby the magnetic field lines bring the charged particles towards the poles. On Earth, we get aurorae when those particles slam into the atmosphere, but Ganymede has no significant atmosphere. Instead, those particles hit the icy surface.
As observed by Juno’s Jovian Infrared Auroral Mapper (JIRAM), the plasma alters the ice. On the equator, the ice is in a crystalline structure. At the pole, the ice is amorphous and the constant bombardment of plasma alters how the water molecules in the ice behave with respect to one another.
"The JIRAM data show the ice at and surrounding Ganymede's north pole has been modified by the precipitation of plasma," Alessandro Mura, a Juno co-investigator at the National Institute for Astrophysics in Rome, said in a statement. "It is a phenomenon that we have been able to learn about for the first time with Juno because we are able to see the north pole in its entirety."
JIRAM’s main job is to study the infrared emission from Jupiter's weather layer, below its swirling cloud cover. However, researchers have also used the instrument for more than just that.
"These data are another example of the great science Juno is capable of when observing the moons of Jupiter," said Giuseppe Sindoni, program manager of the JIRAM instrument for the Italian Space Agency.
The images were collected on December 26, 2019, at about 100,000 kilometers (62,000 miles) from the surface of the Moon. Juno is expected to continue work for another year. On July 30, 2021, the spacecraft will be deorbited into Jupiter to eliminate the risk of contaminating the ice moons that surround the planet.
This won’t be the last we hear about Ganymede this decade. The European Space Agency is planning to launch JUICE (JUpiter ICy moons Explorer) in 2022, which will explore Ganymede, Europa, and Callisto from 2029.