Before NASA’s Juno objective, 3 of Jupiter’s 4 biggest moons, called Galilean moons– Io, Europa, and Ganymede– were revealed to produce these unique auroral signatures.

Callisto, the most far-off of the Galilean moons, stayed a secret.

Regardless of numerous efforts utilizing the NASA/ESA Hubble Space Telescope, Callisto’s footprint had actually shown evasive, both due to the fact that it is faint and since it usually lies atop the better primary auroral oval, the area where aurorae are shown.

NASA’s Juno objective, orbiting Jupiter because 2016, uses unmatched close-up views of these polar light programs.

To image Callisto’s footprint, the primary auroral oval requirements to move aside while the polar area is being imaged.

And to offer Juno’s toolbox of instruments studying fields and particles, the spacecraft’s trajectory need to bring it throughout the electromagnetic field line connecting Callisto and Jupiter.

These 2 occasions serendipitously took place throughout Juno’s 22nd orbit of the huge world, in September 2019, exposing Callisto’s auroral footprint and offering a sample of the particle population, electro-magnetic waves, and electromagnetic fields connected with the interaction.

Jupiter’s electromagnetic field extends far beyond its significant moons, taking a huge area (magnetosphere) covered by, and buffeted by, the solar wind streaming from our Sun.

Simply as solar storms in the world press the northern lights to more southern latitudes, Jupiter’s aurorae are likewise impacted by our Sun’s activity.

In September 2019, a huge, high-density solar stream buffeted Jupiter’s magnetosphere, briefly exposing– as the auroral oval approached Jupiter’s equator– a faint however unique signature connected with Callisto.

This discovery lastly validates that all 4 Galilean moons leave their mark on Jupiter’s environment, which Callisto’s footprints are continual just like those of its brother or sisters, finishing the household picture of the Galilean moon auroral signatures.

“Our observations verify the electrodynamic coupling in between Callisto and Jupiter,” stated Dr. Jonas Rabia, a scientist at the Institut de Recherche en Astrophysique et Planétologie and CNRS, and associates.

“This coupling will be additional evaluated by NASA’s JUICE objective, effectively released in April 2023, which will consistently go to Callisto and its regional environment, making it possible for a much better characterization of the interaction of Callisto with Jupiter’s magnetosphere.”

“The reported in situ and remote observations finish the household picture of Galilean moon auroral footprints, and deal with the longstanding secret regarding whether Callisto’s electro-magnetic interaction is essentially various from the inner 3 Galilean satellites.”

“The observed resemblances, both in the auroral structure and the electron in situ residential or commercial properties, point towards a universal physical system at work for moon-planet and planet-star magnetospheric interactions, pertinent for other double stars that are just available from another location, in the Solar System and beyond.”

The group’s paper was released today in the journal Nature Communications

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J. Rabia et al2025. In situ and remote observations of the ultraviolet footprint of the moon Callisto by the Juno spacecraft. Nat Commun 16, 7791; doi: 10.1038/ s41467-025-62520-4