These images that the JIRAM instrument on board NASA’s Juno spacecraft took on December 26, 2019, provide the first infrared mapping of the northern Ganymede border. The frozen water molecules detected at both poles do not have an appreciable order of arrangement and a different infrared signature than ice at the equator. Image credit: NASA / JPL-Caltech / SwRI / ASI / INAF / JIRAM
Juno’s infrared images provide the first glimpse of Ganymede’s icy north pole.
On the way to December 26, 2019, flyby of Jupiter, POTThe Juno spacecraft flew in proximity to the north pole of the ninth largest object in the solar system, the moon Ganymede. Infrared images collected by the spacecraft’s Jovian Infrared Auroral Mapper (JIRAM) instrument provide the first infrared mapping of the northern border of the massive moon.
Larger than the planet Mercury, Ganymede is primarily 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 path for plasma (charged particles from the Sun) to enter our atmosphere and create auroras. 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. The bombardment has a dramatic effect on the Ganymede ice.
Ganymede’s north pole can be seen in the center of this annotated image taken by the JIRAM infrared camera aboard NASA’s Juno spacecraft on December 26, 2019. The thick line is 0 degrees longitude. Credit: NASA / JPL-Caltech / SwRI / ASI / INAF / JIRAM
“The JIRAM data shows that the ice at and around the north pole of Ganymede has been modified by plasma precipitation,” said Alessandro Mura, a Juno co-researcher at the National Institute of Astrophysics in Rome. “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.”
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. In fact, 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.
“These data are another example of the great science that Juno is able to observe when observing Jupiter’s moons,” said Giuseppe Sindoni, program manager of the JIRAM instrument for the Italian Space Agency.
JIRAM was designed to capture infrared light emerging from inside Jupiter, testing the weather layer up to 30 to 45 miles (50 to 70 kilometers) below Jupiter’s clouds. But the instrument can also be used to study the moons Io, Europa, Ganymede, and Callisto (also known collectively as the Galilean moons for their discoverer, Galileo).
Knowing that the summit of Ganymede would be in sight of Juno on Dec. 26 flyby of Jupiter, the mission team programmed the spacecraft to rotate so that instruments such as JIRAM could see the surface of Ganymede. As it circled its closest approach to Ganymede, at about 62,000 miles (100,000 kilometers), JIRAM collected 300 infrared images of the surface, with a spatial resolution of 14 miles (23 kilometers) per pixel.
The secrets of Jupiter’s largest moon revealed by Juno and JIRAM will benefit the next mission to the frozen world. ESA’s (European Space Agency) JUpiter ICons moons Explorer mission is slated to begin a 3 1/2 year exploration of Jupiter’s giant magnetosphere, its turbulent atmosphere, and its icy moons Ganymede, Callisto, and Europe from 2030. NASA is providing an Ultraviolet Spectrograph Instrument, along with subsystems and components for two additional instruments: the Particle Environment Package and the Radar for Icy Moon Exploration experiment.
NASA’s Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, administers the Juno mission for principal investigator Scott Bolton of the Southwest Research Institute in San Antonio. Juno is part of NASA’s New Frontiers Program, which is managed at NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Scientific Mission Directorate in Washington. The Italian Space Agency (ASI) contributed the Jovian Infrared Auroral Mapper. Lockheed Martin Space in Denver built and operates the spacecraft.
