Scientists from the United States, Europe, and China utilized the Ultraviolet Spectrometer (UVS) on NASA’s Juno spacecraft to meticulously map the auroral patch structure on Ganymede, Jupiter’s moon, revealing similarities to Earth’s auroras. Their groundbreaking research indicates that interactions between magnetic fields and charged particles could be the universal driver of auroras, enhancing our understanding of magnetospheres across the solar system.
Artist’s concept of the aurora borealis on Jupiter’s moon Ganymede. Image credits: NASA/ESA/G. Bacon, STScI/J. Saur, University of Cologne.
Ganymede stands out as the only known moon to possess its intrinsic magnetic field, creating a miniature magnetosphere nested within the vast magnetosphere of Jupiter.
The auroral emissions primarily stem from oxygen at wavelengths of 130.4 nm and 135.6 nm, triggered by precipitating electrons.
In a recent groundbreaking study, researcher Philippe Gusbin from the University of Liège and his team examined ultraviolet observations of Ganymede conducted on June 7, 2021, by the Juno spacecraft.
They identified multiple auroral spots in Ganymede’s leading downstream hemisphere.
These patches typically measure about 50 km in size, with brightness levels soaring to around 200 Rayleigh.
“Auroras on Ganymede are driven by the precipitation of electrons into its thin oxygen atmosphere,” explained Gusbin.
“Previous observations of Ganymede’s auroras were limited in detail due to the spatial constraints of ground-based methods, which couldn’t resolve the fine structures commonly observed in planetary auroras.”
The morphology and scale of Ganymede’s auroras closely resemble the auroral ‘beads’ found on Earth prior to magnetospheric substorms and in Jupiter during ‘dawn storms.’
The lack of a similar patch in the southern hemisphere could stem from observational geometry, but it may also reflect an asymmetry tied to Ganymede’s location in Jupiter’s plasma disk.
“Auroral ‘beads’ are also present in the auroras of Earth and Jupiter, where they correlate with substorms and dawn storms—major magnetospheric reorganizations that release significant energy and induce intense auroral activity,” noted Dr. Alessandro Moirano, a postdoctoral researcher at the University of Liège and the National Institute of Astrophysics in Rome.
This discovery implies that similar physical processes may govern magnetospheres, despite variations in scale and environmental conditions.
“Juno’s close flyby of Ganymede lasted under 15 minutes, and it will not revisit Ganymede, leaving us unsure about the frequency of these patches or how they may evolve,” remarked Dr. Bertrand Bonfont, an astrophysicist at the University of Liège.
“Fortunately, ESA’s JUICE mission is currently en route to Jupiter and is set to arrive in 2031. This mission will conduct detailed observations of Ganymede.”
“Equipped with a similar ultraviolet spectrometer to that of Juno, this spacecraft will facilitate long-term observations that could reveal more about the evolution of Ganymede’s aurora and potentially uncover new mysteries.”
For further reading, refer to a paper published in Astronomy and Astrophysics.
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A. Moirano et al. 2026. High spatial resolution ultraviolet observations of Ganymede’s aurora patches by Juno. Constraints on the magnetospheric source region. A&A 706, L16; doi: 10.1051/0004-6361/202558379
Source: www.sci.news
