Jupiter's auroras form when high-energy particles enter the planet's atmosphere near its magnetic poles and collide with gas atoms. Unlike Earth's auroras, which are driven mainly by solar storms, Jupiter's immense magnetic field draws in charged particles not only from the solar wind but also from its volcanic moon Io. Io's volcanic eruptions eject particles that can escape the moon's gravity and enter Jupiter's magnetosphere, adding to the auroral spectacle. As these particles are accelerated to extreme speeds, they collide with Jupiter's atmosphere, generating the powerful light displays observed.
Webb's Near-InfraRed Camera (NIRCam) captured this dynamic activity on Christmas Day 2023. Jonathan Nichols, leading the study from the University of Leicester, described the experience as a thrilling surprise. "What a Christmas present it was - it just blew me away!" he said. "We wanted to see how quickly the auroras change, expecting it to fade in and out ponderously, perhaps over a quarter of an hour or so. Instead, we observed the whole auroral region fizzing and popping with light, sometimes varying by the second."
Their findings reveal that the trihydrogen ion (H3+) emissions are far more variable than previously thought, providing new clues about the heating and cooling processes in Jupiter's upper atmosphere.
In an unexpected twist, simultaneous ultraviolet observations by the Hubble Space Telescope revealed a puzzling discrepancy. "Bizarrely, the brightest light observed by Webb had no real counterpart in Hubble's pictures," Nichols explained. "This has left us scratching our heads. In order to cause the combination of brightness seen by both Webb and Hubble, we need to have an apparently impossible combination of high quantities of very low energy particles hitting the atmosphere - like a tempest of drizzle! We still don't understand how this happens."
Future studies will compare these Webb observations with data from NASA's Juno spacecraft, aiming to unravel the mysterious bright emission. These insights may also inform the upcoming Jupiter Icy Moons Explorer (Juice) mission by the European Space Agency, which is set to study Jupiter and its ocean-bearing moons Ganymede, Callisto, and Europa. Juice will use its seven scientific instruments, including two imagers, to further investigate Jupiter's complex magnetic environment.
These findings were published in Nature Communications and were part of Webb's Cycle 2 observing programme #4566 and Hubble's observing programme #17471.
Webb is the largest, most powerful telescope ever launched into space. ESA contributed to the mission by providing the launch service, including the adaptation of the Ariane 5 launch vehicle, as well as the NIRSpec spectrograph and 50% of the MIRI instrument, developed in collaboration with JPL and the University of Arizona.
Research Report:Nature Communications
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