The James Webb Space Telescope (JWST) has uncovered surprising interactions between Jupiter’s moons and the planet’s auroras, revealing a cold spot in its atmosphere linked to these celestial bodies. This phenomenon occurs as the moons influence Jupiter’s vast magnetic field, effectively creating “footprints” in the auroral displays that light up the gas giant.
The research, led by Katie Knowles, a Ph.D. researcher at Northumbria University, highlights how Jupiter’s four largest moons—Io, Europa, Ganymede, and Callisto—interact with the planet’s magnetic environment. This interaction causes charged particles to travel along magnetic field lines, leading to collisions in Jupiter’s atmosphere that produce these auroras. In a statement, Knowles explained that, “the moons constantly interact with the magnetic field and plasma surrounding the planet, creating auroral footprints that map to where the moons orbit around Jupiter.”
Jupiter’s auroras are generated similarly to those on Earth, where charged particles from the solar wind collide with the planet’s magnetic field. However, the unique contributions from its moons significantly affect the brightness and structure of these auroras. Notably, the phenomenon is intensified by the Io Plasma Torus, formed from the volcanic activity on Io, which ejects vast amounts of charged particles into the surrounding space.
In September 2023, researchers Henrik Melin and Tom Stallard utilized the JWST to capture snapshots of Jupiter’s auroras, focusing on the area where these events rotate into view. In analyzing the data, Knowles discovered an unexpected cold spot associated with Io’s auroral footprint. While the overall temperature of the aurora was recorded at a steady 919 degrees Fahrenheit (493 degrees Celsius), the cold spot measured only 509 degrees Fahrenheit (265 degrees Celsius). This significant temperature disparity indicates a unique interaction between the charged particles and Jupiter’s atmosphere.
Furthermore, the density of ions in this cold region was notably higher than any previously recorded. The trihydrogen cation (H3+) was particularly prevalent, with its ion density averaging three times greater than the rest of the aurora. Within the cold spot, variations in ion density reached an astonishing 45 times, demonstrating extreme fluctuations over mere minutes. Knowles remarked, “We found extreme variability in both temperature and density within Io’s auroral footprint that happened on the timescale of minutes.”
While Jupiter is known for having the most powerful auroras in the solar system, it is not the only planet with such phenomena. Earth also has auroras, but the Moon does not impact them due to its weaker interaction with Earth’s magnetic field. In contrast, Saturn’s moon Enceladus, which releases particles through its geysers, does influence the auroras on its host planet. This raises the possibility that similar cold spot phenomena could exist in other planetary systems.
This research opens up new avenues for studying Jupiter and its moons, as well as other gas giants. According to Knowles, “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 further afar.”
Despite these findings, many questions remain unanswered. The cold spot observed was only captured in a single image, prompting inquiries about its frequency, the mechanisms that trigger its appearance, and how the magnetic environment of Jupiter influences its occurrence. To further investigate, Knowles has been awarded observation time on NASA’s Infrared Telescope Facility in Hawaii, scheduled for January 2026. This project will track various auroral footprints over six nights as they rotate with Jupiter, providing deeper insights into these dynamic atmospheric phenomena.
The results of the JWST’s observations were detailed in a paper published on March 3, 2024, in the journal Geophysical Research Letters.
