Jupiter Auroras and Callisto Footprint Discovery by Juno

Introduction
Jupiter auroras and Callisto footprint are now at the center of an exciting breakthrough in planetary science. For years, scientists knew that Io, Europa, and Ganymede each created auroral signatures in Jupiter’s atmosphere. But Callisto, the most distant Galilean moon, remained elusive — until NASA’s Juno spacecraft finally captured its mark.

The Missing Footprint

While Hubble observations showed auroral “satellite footprints” from Jupiter’s other moons, Callisto’s was hidden. It was both faint and often masked by the planet’s main auroral oval.

A Serendipitous Discovery

During Juno’s 22nd orbit in September 2019, two rare conditions aligned: the auroral oval shifted aside, and Juno crossed the magnetic field line linking Callisto to Jupiter. This serendipitous timing finally revealed Callisto’s faint aurora.

Solar Wind’s Role

Jupiter’s auroras are shaped by solar wind, much like Earth’s northern lights. In September 2019, a powerful solar stream struck Jupiter, briefly pushing the auroral oval toward the equator. This movement exposed Callisto’s footprint and confirmed its presence.

The Complete Galilean Family

With this discovery, scientists confirmed that all four Galilean moons leave unique auroral imprints. Callisto’s signature completes the auroral “family portrait,” deepening our understanding of Jupiter’s magnetosphere.

Scientific Publication

The discovery was led by Jonas Rabia and an international team at IRAP, CNRS, CNES in Toulouse, France. Their paper, “In situ and remote observations of the ultraviolet footprint of the moon Callisto by the Juno spacecraft,” appeared in Nature Communications on September 1, 2025.