Jupiter’s small moons may tell the story its famous icy moons cannot

The European Space Agency’s Jupiter Icy Moons Explorer (JUICE) is on a eight-year journey to the gas giant, carrying instruments designed to study the planet’s three largest icy moons: Ganymede, Europa, and Callisto. But while these moons dominate the mission’s scientific objectives, JUICE’s trajectory will also place it within range of Jupiter’s 94 other satellites—many of which have never been studied in detail.

According to a recent paper in Space Science Reviews, JUICE’s bonus science could transform our understanding of these minor moons, particularly Io, the most volcanically active body in the solar system.

JUICE’s JANUS camera will capture Io’s surface at resolutions of 6–12 kilometers per pixel, tracking changes in its lava flows and volcanic plumes. Meanwhile, the probe’s UVS instrument will monitor sulfur dioxide emissions and auroral activity, offering clues about Io’s interaction with Jupiter’s powerful magnetosphere. These observations could help explain how tidal forces from Jupiter generate the moon’s extreme volcanic activity, which releases 80 trillion watts of energy during its largest eruptions.

For context, that’s roughly equivalent to the output of 8,000 nuclear power plants—all from a moon just slightly larger than Earth’s own.

Beyond Io, JUICE’s instruments will also scrutinize Amalthea, a small inner moon whose unusual brightness has puzzled scientists for decades. Dubbed “Amalthea’s Paradox,” the moon reflects far more light than its surface composition should allow, suggesting the presence of unknown materials or processes. JUICE’s spectral data could finally resolve this mystery, providing insights into the moon’s origins and its role in Jupiter’s ring system.

Perhaps the most ambitious of JUICE’s secondary objectives is a potential flyby of Kallichore, an irregular moon orbiting Jupiter at a distance of over 23 million kilometers. If executed, this would mark the first close-up study of an irregular Jovian moon, offering a rare glimpse into the outer reaches of the Jupiter system. The data could help scientists determine whether these distant moons are captured asteroids or remnants of the planet’s early formation.

While JUICE’s primary mission remains focused on the big three icy moons, its bonus science could prove just as transformative for our understanding of Jupiter’s complex and dynamic satellite system.

For more details on JUICE’s mission objectives, see the full paper in Space Science Reviews.

For source context, compare NASA Science, European Space Agency and Wikipedia background.