For the first time, new images made possible by NASA’s James Webb Space Telescope have revealed the glow of Neptune’s elusive aurora.
Although auroras have been observed on other planets in our solar system, the phenomenon has never been documented in imagery of the eighth planet from the Sun. The new Webb images reveal the planet’s aurora as areas of hazy cyan blue (see below).
Auroras result from highly energetic particles from the Sun trapped in a planet’s magnetic field, which carries them toward its upper atmosphere. As these particles release energy, they produce the luminous phenomenon often associated with the polar regions when seen here on Earth.
Past studies had already hinted at the presence of auroral activity on Neptune, although no direct observations had ever been made until now.
Neptune's aurora
In the images above, earlier images of Neptune obtained with the Hubble Space Telescope appear on the left, with new composite imagery that combines the Hubble view with Webb Near-Infrared Spectrograph (NIRSpec). Neptune’s aurora is revealed in areas in the image to the right shown in cyan (Credit: NASA, ESA, CSA, STScI, Heidi Hammel (AURA), Henrik Melin (Northumbria University), Leigh Fletcher (University of Leicester), Stefanie Milam (NASA-GSFC)).
Henrik Melin, a researcher with Northumbria University and lead author of a new paper discussing the discovery, said the imagery of Neptune’s aurora wouldn’t have been possible without Webb’s powerful near-infrared imaging capabilities.
“It was so stunning to not just see the auroras,” Melin recently said, adding that “the detail and clarity of the signature really shocked me.” Melin participated in the research while at the University of Leicester.
Neptune’s Aurora Comes into Focus
With help from Webb’s powerful Near-Infrared Spectrograph, Melin and the team initially obtained the imagery of Neptune’s elusive aurora in June 2023. Accompanying the new planetary imagery, Webb’s instruments also provided spectrographic information that allowed the team to examine the composition and temperature of the Neptunian ionosphere.
During their groundbreaking observations, Melin and the research team spotted a prominent emission line caused by electromagnetic radiation being released as electrons move from a higher to a lower energy state. In this case, the emission line indicated the presence of H3+, a trihydrogen cation associated with aurora generation.
Heidi Hammel, a Webb interdisciplinary scientist and leader of the Guaranteed Time Observation program for the Solar System, which was responsible for collecting the new data, said that H3+ is one of the prime indicators of auroral activity on all the gas giant planets.
Although auroras were long expected during ground observations of Neptune, none were seen before the new Webb images were collected.
“Only with a machine like Webb have we finally gotten that confirmation,” Hammel said in a statement.
Unearthly Auroras
The research team says Neptune’s aurora differs significantly from the kinds we often see on Earth and those observed on giant planets like Saturn and Jupiter.
Normally associated with the poles of these planets, Neptune’s auroras appear closer to its geographic mid-latitudes. This phenomenon originates from its odd magnetic field, which is offset by around 47 degrees from the planet’s rotational axis. As a result, Neptune’s auroras are similarly displaced from its poles.
The research team says their first detection of the planet’s unusual auroras will provide deeper insights into interactions between Neptune’s magnetic field and particles emanating from the Sun, which are propelled to distant solar system regions.
Additionally, new measurements of Neptune’s temperature—the first such measurements collected since NASA’s Voyager 2 made its famous flyby of the planet decades ago—provide additional insights into why its auroras remain elusive. Neptune’s atmosphere appears to have cooled by several hundred degrees since those initial measurements, a factor that likely may have influenced the intensity of Neptune’s auroras.
levitation bioprinting
The recent images aren’t the first time Webb has revealed unprecedented views of Neptune. In 2022, Neptune’s rings were revealed in stunning detail in images collected by the Webb telescope, which included a view of several of the planet’s moons.
Neptune rings
Neptune’s rings and several of its moons were revealed in striking Webb images collected by the telescope in 2022 (Credit: NASA).
Going forward, future observations of Neptune throughout an entire 11-year solar cycle could provide additional insights into the behavior of the planet’s magnetic field.
Leigh Fletcher, a Leicester University researcher and co-author of the new study detailing the findings, said that in lieu of the ability to send crewed missions to distant giant planets like Neptune anytime soon, robotic probes that visit such destinations can be equipped with instruments that can be finely tuned to collect additional information on Neptune’s auroras.
Fletcher added that NASA’s Webb telescope “has finally opened the window onto this last, previously hidden ionosphere of the giant planets.”
The team’s paper, “Discovery of H3+ and infrared aurorae at Neptune with JWST,” was published in Nature Astronomy on March 26, 2025.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. He can be reached by email atmicah@thedebrief.org. Follow his work atmicahhanks.comand on X:@MicahHanks.