Jupiter’s moons can have surprising effects on the world’s displays of the aurora borealis by “stepping down” on the planet’s giant magnetic environment.
These surprising effects, discovered in observations from the James Webb Space Telescope (JWST), include a cold spot in Jupiter’s atmosphere, and a rapid increase in the density of charged particles.
The article continues below
Jupiter’s northern lights are created in a similar way to Earth’s as charged particles that ride on solar wind slams into Jupiter’s magnetic field and is guided down towards the gas giant’s poles. When they enter the atmosphere, they collide with atoms and molecules, causing them to glow. However, by interacting with Jupiter’s magnetic field, the four largest moons – the Galilean moons Io, Europe, Ganymede and Callisto — can leave an imprint on the northern lights.
The footprints are exacerbated by a phenomenon known as the Io Plasma Torus. Io is the solar systemits most volcanic body, and the volcanoes spew tons of charged particles that drift into orbit around Jupiter, forming the plasma torus held in place by Jupiter’s magnetic field. As the Galilean moons orbit Jupiter, they interact with the plasma torus and magnetic field, driving ions toward Jupiter’s atmosphere, contributing to the aurora and generating electrical currents that affect how bright the aurora footprint is.
Previous multi-wavelength measurements have tracked how bright the northern lights, and these footprints, can get. In September 2023, however, Northumbria’s Henrik Melin and Tom Stallard used to take snapshots of the area on Jupiter where auroral events rotated into view. By looking at the edge of Jupiter’s disk, JWST was able to examine the side profile of Jupiter’s atmosphere just below an aurora.
When Knowles analyzed this data, she found something unexpected.
JWST took five snapshots, and in four of them everything looked normal. But in one snapshot, a cold spot appeared in the atmosphere beneath an aurora linked to Io’s footprint. While the rest of the aurora had a steady temperature of 919 degrees Fahrenheit (493 degrees Celsius), the cold spot was “only” 509 degrees Fahrenheit (265 degrees Celsius).
The density of ions flowing into the upper atmosphere to drive the aurora around the cold spot was also far higher than had ever been measured before. A particularly abundant ion present was the trihydrogen cation (H3+) and the ion density was on average three times greater than the rest of the northern lights. Also, within the cold spot, densities can vary by up to 45 times in just that small area.
“We found extreme variability in both temperature and density within Io’s auroral footprint that occurred on the time scale of minutes,” Knowles said. “This tells us that the stream of high-energy electrons crashing into Jupiter’s atmosphere is changing incredibly quickly.”
Jupiter’s auroras are the most powerful in the solar system, but they’re not the only auroras found in our corner of the neighborhood. Of course it’s the Earth’s Northern Lights – but Earth’s moon does not leave a footprint on our planet’s aurora borealis because it does not interact strongly enough with Earth’s magnetic field. However Saturnits moon Enceladuswhich spew particles into space via their water geysers, affect the aurora borealis on the ringed planet. It is therefore possible that this freezing point phenomenon also occurs there.
“This work opens up entirely new ways of studying not only Jupiter and its other Galilean moons, but potentially other giant planets and their moon systems,” Knowles said. “We see Jupiter’s atmosphere reacting to the moons in real time, giving us insight into processes occurring throughout our solar system and perhaps further afield.”
However, questions remain.
For example, the cold spot was only seen in one image. How often do they occur, what causes them to turn on and off, and how are they affected by the conditions of Jupiter’s magnetic environment?
Knowles is already searching for answers. In January 2026, she was assigned time at NASA’s Mauna Kea Infrared Telescope Facility in Hawaii to track the various aurora footprints over six nights as they rotate with the planet, and she is currently analyzing the data.
The JWST observations are described in an article published on March 3 in the journal Geophysical Research Letters.
