The moon Ganymede of Jupiter, the largest planetary satellite in the solar system, is the only moon with its own magnetic field, not to mention being the most differentiated of all of its kind, and it possibly possesses "a subsurface ocean of liquid water."

According to a Phys.org article, what's said to be the most intriguing moon was studied by "the early Jupiter flybys" which Pioneer and Voyager spacecraft made, although today's understanding rests extensively on the observation made by the Galileo orbiter of NASA from 1995 to 2003.

A group of researchers now present some of the firsts in situ observations of the Jupiter moon since the Galileo mission's conclusion.

Specifically, the team used a tool known as JIRAM or the Jovian Infrared Auroral Mapper, onboard Juno spacecraft of NASA to capture images and spectra of the moon's north polar region.

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Science Times - Water Ice Mapped Across Northern Part of Ganymede, the Largest Moon in the Solar System
(Photo: Wikimedia Commons)
Diameter comparison of Ganymede, Moon, and Earth. The scale is approximately 29 kilometers per pixel.


JIRAM Enabled

In December 2016, Juno passed this Jupiter moon at a roughly 100,000-kilometer distance, allowing JIRAM to map this particular region at a maximum spatial resolution of 23 kilometers a pixel.

As the spacecraft Juno flies past Ganymede, it can observe physical sites on the moon's surface from different angles.

By comparing the brightness of such regions throughout a range of observation, as well s illumination geometries, the authors devised a photometric model for the surface reflectance of Ganymede.

The study investigators observed that wavelength-reliant reflectance associations sometimes break down in the vicinity of comparatively fresh craters, probably due to a larger average size of ice grains in these sites.

In relation to the tool, the JIRAM image was developed in December 2018. Its instrument uncovers excessively high temperatures at the areas of a volcanic eruption on Io.

Such an observation was taken during the similar fully-eclipsed period of images produced from the JunoCam and Stellar Reference Unit.

Mapping the Distribution of Water Ice

Integrating their model with spectral observations of the "two-micrometer water ice absorption band" enabled the authors to map the north polar region's water ice distribution.

Where such approximations overlapped with maps that resulted from Earth-based telescopic observations, the study authors discovered essentially good agreement.

Furthermore, such a resemblance allowed them to extend the worldwide water ice map for the Jupiter moon to much more latitudes the north.

Observations in other spectral bands exposed the presence or existence of non-water chemical species on Ganymede's surface.

As indicated in the study, the said chemical species comprises possible discovery of "hydrated magnesium salts, carbon dioxide, and a range of organic molecules."

The Ganymede Moon

Ganymede is said to be named for a boy who was made "cupbearer" by Zeus for the ancient Greek gods: Jupiter to the Romans.

Essentially, this largest moon in the solar system comprises three main layers. One is the metallic icon's sphere at the center. Another layer is the rock's spherical shell that surrounds the core. The third and last is a spherical shell, mostly of ice surrounding the rock shell and the center.

The ice shell on the outside is described to be very thick, approximately 497 miles thick. The surface is the topmost of the ice shell.

Even though it is mostly ice, the ice shell might comprise some rocks mixed in. According to scientists, they believe, there must be a "fair amount of rock in the ice near the surface." The Magnetic field of Ganymede is embedded inside the massive magnetosphere of Jupiter.

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