A series of infrared images taken by the Juno spacecraft provide the first glimpse of Ganymede's icy north pole. Image Credit: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM.

Unprecedented Images Reveal Previously-Unseen Parts of Jupiter’s Moon Ganymede

Never before have we been able to see what the northern pole of Ganymede was like until now.

Scientists have revealed the first images of the north pole of Jupiter’s gigantic moon Ganymede.


NASA’s Juno mission has obtained the first images of the northern edge of Jupiter’s moon Ganymede, the ninth-largest object in the Solar System.

Infrared images collected by the spacecraft’s Jovian Infrared Auroral Mapper (JIRAM) instrument – during a Jupiter flyby on December 26, 2019 – provide the first infrared mapping of the northern border of the huge moon.

The only moon in the solar system that is larger than the planet Mercury, at 5,262 kilometers in diameter, Ganymede is mainly made up of water ice.

Its composition contains fundamental clues to understand the evolution of the 79 Jovian moons from the time of their formation to the present day.

Ganymede is also the only moon in the solar system with its own magnetic field.

On Earth, the magnetic field provides a way for plasma (charged particles from the Sun) to enter our atmosphere and create an aurora.

Since Ganymede has no atmosphere to impede its progress, the surface of its poles is constantly being bombarded by plasma from Jupiter’s gigantic magnetosphere.

Ganymede's North Pole can be seen in this image taken by the JIRAM infrared imager aboard NASA's Juno spacecraft on Dec. 26, 2019. Image Credit: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM.
Ganymede’s North Pole can be seen in this image taken by the JIRAM infrared imager aboard NASA’s Juno spacecraft on December 26, 2019. Image Credit: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM.

The bombardment has a dramatic effect on the Ganymede ice.

“The JIRAM data shows the ice at and surrounding Ganymede’s north pole has been modified by the precipitation of plasma,” revealed Alessandro Mura, a Juno co-investigator at the National Institute for Astrophysics in Rome.

“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.”

The ice near both poles of the moon is amorphous. This is because the charged particles follow the lines of the moon’s magnetic field to the poles, where they impact, wreaking havoc on the ice there, preventing it from having an ordered (or crystalline) structure.

The frozen water molecules detected at both poles do not have an appreciable order for their arrangement, and amorphous ice has a different infrared signature than crystalline ice found at the Ganymede equator.

The Juno mission has greatly contributed to our understanding of not only Jupiter, but the entire Jovian system, and especially its larger moons like Ganymede.

Scientists designed the JIRAM instrument to capture infrared light emerging from inside Jupiter, analyzing the meteorological layer 50 to 70 kilometers below Jupiter’s clouds.

However, the researchers also revealed that the instrument could also be used to study the moons Io, Europa, Ganymede, and Callisto (also known collectively as the Galilean moons by their discoverer, Galileo Galilei).

Knowing that the peak of Ganymede would be in view of Juno on December 26 during a Jupiter flyby, the mission team programmed the spacecraft to rotate so that its instruments such as the JIRAM could see the surface of Ganymede.

As the spacecraft circled its closest approach to Ganymede, some 100,000 kilometers away, JIRAM collected 300 infrared images of the surface, with a spatial resolution of 23 kilometers per pixel.

What Juno learned from its flyby will benefit future exploratory missions to the Jovian system.

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