Jupiter’s moons are having an unexpected impact on the planet’s auroral displays, as revealed by recent observations from the James Webb Space Telescope (JWST). These findings indicate that the moons create cold spots in Jupiter’s atmosphere, along with a notable increase in the density of charged particles. This interaction occurs as the moons influence Jupiter’s extensive magnetic environment, leading to unique signatures in the planet’s auroras.
The Galilean moons—Io, Europa, Ganymede, and Callisto—continuously interact with Jupiter’s magnetic field and the surrounding plasma. This interaction causes highly energetic particles to travel along magnetic field lines, impacting the planet’s atmosphere and generating auroral footprints that correspond to the moons’ orbits. According to Katie Knowles, a Ph.D. researcher at Northumbria University in the U.K., the moons significantly affect the auroral phenomena through a process involving the Io Plasma Torus.
Io, known as the most volcanic body in the solar system, ejects vast amounts of charged particles that drift into orbit around Jupiter. These particles form the plasma torus, which is held in place by Jupiter’s magnetic field. As the Galilean moons orbit, they engage with this torus and the magnetic field, driving ions towards Jupiter’s atmosphere, thereby enhancing the auroras and generating electrical currents that influence the brightness of the resulting footprints.
In September 2023, researchers Henrik Melin and Tom Stallard from Northumbria University utilized the JWST to capture snapshots of auroral events on Jupiter. The telescope focused on the planet’s edge, allowing it to probe the atmospheric profile beneath an aurora. Knowles analyzed data from five snapshots, noting that four showed typical patterns. However, one image revealed an unexpected cold spot associated with Io’s auroral footprint. While the rest of the aurora maintained a temperature of approximately 919 degrees Fahrenheit (493 degrees Celsius), the cold spot registered at just 509 degrees Fahrenheit (265 degrees Celsius).
Furthermore, the density of ions entering the upper atmosphere around the cold spot was exceptionally high, far exceeding previous measurements. Notably, the trihydrogen cation (H3+) was present in densities that were, on average, three times greater than the surrounding aurora. Within the cold spot, ion densities exhibited fluctuations of up to 45 times in a small area. “We found extreme variability in both temperature and density within Io’s auroral footprint that happened on the timescale of minutes,” Knowles stated. This rapid change suggests that the flow of high-energy electrons striking Jupiter’s atmosphere is highly dynamic.
While Jupiter hosts the most powerful auroras in the solar system, it is not alone in this phenomenon. Earth’s auroras exist, but the Moon does not influence them due to its insufficient interaction with Earth’s magnetic field. In contrast, Enceladus, a moon of Saturn, actively ejects particles through its water geysers, impacting Saturn’s auroras. The findings from Jupiter’s auroras suggest that similar cold spot phenomena might also occur in other planetary systems.
“This work opens up entirely new ways of studying not just Jupiter and its other Galilean moons, but potentially other giant planets and their moon systems,” Knowles remarked. The ability to observe Jupiter’s atmosphere responding to its moons in real-time offers valuable insights into processes that occur throughout our solar system and potentially beyond.
Despite these breakthroughs, questions remain regarding the cold spots. The phenomenon was only observed in one image, prompting inquiries about its frequency, causes, and the influences of Jupiter’s magnetic environment. Knowles is actively pursuing answers; she has been awarded time in January 2026 on NASA’s Infrared Telescope Facility in Hawaii to monitor various auroral footprints over six nights as they rotate with the planet. This ongoing research aims to deepen the understanding of Jupiter’s complex atmospheric dynamics.
The JWST observations are documented in a paper published on March 3, 2024, in the journal Geophysical Research Letters, marking a significant advancement in planetary science and our comprehension of auroral phenomena.
