Space telescope captures Neptune’s auroras for first time

Images of bright auroral activity on Neptune have been captured for the first time.

A team of scientists, led by Northumbria University, and including a University of Reading space expert, used NASA’s James Webb Space Telescope to look deep into space. Using data captured by Webb, researchers have for the first time captured images of auroras occurring on Neptune.

Their findings, published today (Wednesday, 26 March) in the journal Nature Astronomy, also describe a surprising change in Neptune’s temperature over the past 30 years.

Dr James O’Donoghue co-authored the study from the University of Reading. He said: “Nobody has seen Neptune’s auroras since 1989, despite our team’s best efforts using the world's largest telescopes. It has been a real head-scratcher. Thanks to the sensitivity of the James Webb Space Telescope, we've finally found it. 

“What's most exciting to me is that we can even measure its temperature. It turns out that Neptune has cooled by hundreds of degrees since 1989, which means it now emits just 1% the amount of light it did more than three decades ago. This explains why it has been impossible to detect until now.”

More studies to come

Auroras occur when energetic particles from the Sun get trapped in a planet's magnetic field and strike the upper atmosphere, creating a signature glow. Though astronomers had seen hints of auroral activity on Neptune during Voyager 2's 1989 flyby, confirming them remained elusive until now, despite successful detections on Jupiter, Saturn, and Uranus.

Using the James Webb Space Telescope, which launched in December 2021, scientists obtained data in June 2023 that revealed the presence of trihydrogen cation (H3+), a clear marker of auroras. In Webb's images, Neptune's auroras appear as cyan-coloured splotches. Unlike Earth's auroras which appear at the poles, Neptune's auroras are located at mid-latitudes – roughly equivalent to where South America is located on Earth – due to its unusual magnetic field, which is tilted 47 degrees from its rotation axis.

The Webb observations also showed Neptune's upper atmosphere has cooled dramatically since 1989, with temperatures just over half of what they were then. This explains why the auroras remained hidden for so long, as colder temperatures result in much fainter auroras. This cooling is particularly surprising given Neptune sits over 30 times farther from the Sun than Earth.

Scientists now plan to study Neptune over a full 11-year solar cycle to better understand its bizarre magnetic field and atmospheric changes, potentially revealing why its magnetic field is so unusually tilted.

Image: Neptune’s auroras as captured by the Hubble Space Telescope and James Webb Space Telescope. Image credit: NASA, ESA, CSA, STScI, Heidi Hammel (AURA), Henrik Melin (Northumbria University), Leigh Fletcher (University of Leicester), Stefanie Milam (NASA-GSFC)

Melin, H., Moore, L., Fletcher, L. N., Hammel, H. B., Stallard, T. S., Milam, S. N., Roman, M., King, O. R., Thomas, E. E., Wang, R., Tiranti, P. I., Harkett, J., & Knowles, K. L. (2025). Discovery of $${{\bf{H}}}_{\mathbf{3}}^{\mathbf{+}}$$ and infrared aurorae at Neptune with JWST. Nature Astronomy, 1-6. https://doi.org/10.1038/s41550-025-02507-9