Jupiter’s moons have been found to significantly influence the planet’s auroral displays by interacting with its vast magnetic environment. Observations from the James Webb Space Telescope (JWST) revealed unexpected effects, including a cold spot in Jupiter’s atmosphere and a surge in the density of charged particles. These findings enhance our understanding of the complex interactions between Jupiter and its four largest moons—Io, Europa, Ganymede, and Callisto.
The interaction between the moons and Jupiter’s magnetic field generates highly energetic particles. These particles travel along magnetic field lines and collide with the planet’s atmosphere, creating auroral footprints that correspond to the moons’ orbits. According to Katie Knowles, a Ph.D. researcher at Northumbria University, “The moons constantly interact with the magnetic field and plasma surrounding the planet, leading to the creation of these auroral footprints.”
Jupiter’s auroras resemble those on Earth, formed when charged particles from the solar wind encounter the planet’s magnetic field. These particles are funneled towards the poles, where they collide with atmospheric atoms and molecules, producing bright displays. However, the Galilean moons leave distinct imprints on these auroras. The phenomenon is intensified by the Io Plasma Torus, a ring of charged particles released by Io’s numerous volcanoes.
In September 2023, researchers Henrik Melin and Tom Stallard utilized the JWST to capture images of Jupiter’s auroral events. Their study focused on the edge of Jupiter’s disk, allowing them to examine the atmosphere beneath an aurora. The data analysis revealed an intriguing anomaly—one snapshot showed a cold spot beneath Io’s auroral footprint. While the surrounding aurora had a temperature of 919 degrees Fahrenheit (493 degrees Celsius), this cold spot measured only 509 degrees Fahrenheit (265 degrees Celsius).
The density of ions entering Jupiter’s upper atmosphere in this region was astonishingly high. Notably, the presence of the trihydrogen cation (H3+) was significant, with densities averaging three times greater than in the rest of the aurora. Within the cold spot, fluctuations in ion density were observed, varying by as much as 45 times within a short distance. Knowles remarked, “We found extreme variability in both temperature and density within Io’s auroral footprint that happened on the timescale of minutes.”
Jupiter’s auroral lights are the most powerful in the solar system, but other planets also exhibit auroras influenced by their moons. Earth’s moon, for example, does not affect our planet’s auroras due to its weak interaction with Earth’s magnetic field. In contrast, Saturn’s moon Enceladus influences the ringed planet’s auroras by releasing particles from its water geysers, suggesting that similar cold spot phenomena could occur there as well.
This research opens new avenues for studying not only Jupiter and its moons but also other giant planets and their moon systems. Knowles stated, “We’re seeing Jupiter’s atmosphere respond to its moons in real-time, which gives us insights into processes that occur throughout our solar system and perhaps beyond.”
Despite these discoveries, questions remain about the nature of the cold spots. The cold spot was observed in only one image, raising inquiries about their frequency and the underlying mechanisms that cause them to appear and disappear. To investigate further, Knowles has been awarded observing time on NASA’s Infrared Telescope Facility on Mauna Kea, Hawaii, in January 2026. She plans to monitor various auroral footprints over six nights as they rotate with the planet.
The JWST observations are detailed in a paper published on March 3, 2024, in the journal Geophysical Research Letters. This groundbreaking work not only enhances our comprehension of Jupiter’s atmospheric dynamics but also invites further exploration of the intricate relationships between celestial bodies within our solar system.
