Telescope reveals surprising secrets in Jupiter's northern lights

An international team of scientists, led by a PhD researcher from Northumbria University, has made groundbreaking discoveries about a spectacular feature of Jupiter’s northern lights, revealing a never-before-seen temperature structure and dramatic density changes within the top of the giant planet’s atmosphere.

The research, published today in Geophysical Research Letters, provides the first spectral measurements of the infrared  auroral footprints of Io and Europa – brilliant glowing patterns produced by Jupiter’s Galilean moons interacting with its powerful magnetic field.

The observations were captured using the James Webb Space Telescope (JWST), led by an international partnership between NASA, the European Space Agency (ESA), and Canadian Space Agency (CSA), which uses infrared radiation to look deep into space.

Speaking about the findings, lead author Katie Knowles, explains: “These emissions have been measured previously at ultraviolet and infrared wavelengths, but only sporadically in how brightly they shine.  With Webb’s incredible sensitivity, we have been able to extract the physical properties of the auroral footprints for the first time, including the temperature of the upper atmosphere and the ion density, which has never been reported on before.”

Unlike Earth's northern lights, which are primarily driven by the solar wind, Jupiter's aurora includes the impact of its four large Galilean moons – Io, Europa, Ganymede, and Callisto – which create their own ‘mini aurora’ on the planet.

Jupiter is an incredibly fast rotator, and its powerful magnetic field rotates once approximately every 10 hours along with the planet, carrying charged particles with it. However, the moons orbit much more slowly – Io, the innermost Galilean moon, takes around 42.5 hours to complete one orbit around the planet.

As Katie explains: “The moons continuously interact with the magnetic field and plasma surrounding the planet, and that interaction leads to highly energetic particles travelling down magnetic field lines and then crashing into the planet’s atmosphere, creating the auroral footprints, which magnetically map to where the moons orbit.

“Jupiter's aurora is the most powerful and continuously observable of any aurora in the Solar System. What we're seeing with the Webb gives us an unprecedented window into how Jupiter's moons directly affect the top of the planet's atmosphere, as well as the moons themselves, their local environment and their interaction with Jupiter’s magnetic field.”

The study is based on Webb data taken during the time awarded to Dr Henrik Melin and Professor Tom Stallard of Northumbria University. During a 22-hour window of observation time which took place in September 2023, the research team carried out a scan around the edge of Jupiter, chasing the northern lights as they rotated into view. It was during these observations that they also happened to capture the auroral footprints.

However, the footprints created by Io and Europa, did not have the characteristics expected from Jupiter’s main aurora, which contains a lot of hot material. Instead, in one snapshot, they discovered a cold spot within Io's auroral footprint that registered temperatures much lower than expected, with extraordinarily high densities.

Jupiter’s moon, Io, is the most volcanically active body in our solar system, with its volcanoes ejecting about 1,000 kilograms of material into space every second, feeding the dense plasma surrounding Jupiter. Some of this material becomes ionised and forms a doughnut-shaped cloud around Jupiter called the Io plasma torus. As Io moves through its orbit, it generates powerful electrical currents that create Io’s bright auroral footprint.

Katie and her colleagues found that Io’s auroral footprint contained trihydrogen cation  (H₃⁺) densities three times higher than those found in Jupiter's main aurora, with the ion densities changing by a factor of 45 within the same small area.

“We found extreme variability in both temperature and density within Io's auroral footprint on the timescale of minutes,” said Katie. “This tells us that the flow of high-energy electrons crashing into Jupiter's atmosphere is changing incredibly rapidly.

“The cold spot registered temperatures of just 538 Kelvin, or 265°C, compared to 766 Kelvin, or 493°C in the rest of Jupiter’s aurora. The cold spot also contained material three times denser than Jupiter's main aurora, with the highest densities we have ever recorded.”

The findings could extend far beyond Jupiter and open questions about other planetary systems. Saturn's moon, Enceladus, also creates an auroral footprint on the planet, and scientists wonder whether similar phenomena occur there.

“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,” said Katie, who is currently finishing her PhD. “We're seeing Jupiter respond to its moons in real-time, which gives us insights into processes that occur throughout our solar system and perhaps further afar.

“We only saw this phenomenon in one of our five snapshots, which leave us with questions. How often does this occur? Do our current observations represent the “typical” variability? How does it change with space, time, and under different conditions?”

To answer these questions, Katie was awarded over 32 hours of observation time with NASA's Infrared Telescope Facility (IRTF) in Hawaii across six nights in January 2026. This allowed her to watch as the auroral footprint rotated with the planet., She hopes analysis of this data will enable her to determine whether this extreme variability is common or rare.

FURTHER INFORMATION:

Visit the Northumbria University Research Portal to find out more about Katie Knowles’ work.

The paper Short-Term Variability of Jupiter's Satellite Footprints as Spotted by JWST was published in Geophysical Research Letters on 2 March 2026.

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