On 26 December, 2019, the Juno spacecraft’s orbit around Jupiter brought it near the north pole of the ninth-largest object in the solar system, the moon Ganymede. The spacecraft’s Jovian Infrared Auroral Mapper (JIRAM) instrument took the first infrared images of the massive moon’s north pole.
Ganymede only moon in the solar system that is larger than the planet Mercury. It’s mostly water ice. It is also the only moon in the solar system with its own magnetic field. On Earth, the magnetic field provides a pathway for plasma (charged particles from the Sun) to enter our atmosphere and create aurora. Ganymede has no atmosphere to impede the progress of those charged particle, so the surface at its poles is constantly being bombarded by plasma from Jupiter’s gigantic magnetosphere. The bombardment has a dramatic effect on Ganymede’s ice.
The ice near both poles of the moon is amorphous. This is cause by the impact of the plasma on the surface. That pounding prevents the ice from having a crystalline structure.
Image Credit: NASA/ JPL / SWRI / ASI / INAF