Though previous observations had detected auroras on Jupiter produced by three of its four Galilean moons — Io, Europa, and Ganymede — scientists had until now been unable to detect a similar aurora produced by the fourth, Callisto.
The Jupiter orbiter Juno finally accomplished this observation for the first time.
[T]o image Callisto’s footprint, the main auroral oval needs to move aside while the polar region is being imaged. And to bring to bear Juno’s arsenal of instruments studying fields and particles, the spacecraft’s trajectory must carry it across the magnetic field line linking Callisto and Jupiter.
These two events serendipitously occurred during Juno’s 22nd orbit of the giant planet, in September 2019, revealing Callisto’s auroral footprint and providing a sample of the particle population, electromagnetic waves, and magnetic fields associated with the interaction.
The research paper describing this detection has just been published.
These secondary auroras are caused by Jupiter’s powerful magnetic field.
The Juno mission itself is about to end. NASA did not approve a mission extension, and next month the science team will send the spacecraft into Jupiter’s atmosphere, where it will burn up. We will then have to wait five years for Europa Clipper to arrive in Jupiter orbit, followed a year later by Europe’s Juice orbiter.
While the propaganda press is condemning this decision, there is some logic to it. Juno has mostly completed its work. While new knowledge can certainly be gained if it remained operations for three more years, the amount of knowledge will be relatively small. And NASA does face a budget crunch. Better to spend its money on other things that can produce more bang to the buck.
