01-04-2025
North East scientists help capture stunning images of Neptune auroras
Scientists at Northumbria University have captured images of auroral activity on Neptune.
This was achieved using NASA's James Webb Space Telescope, which observes space in infrared radiation.
Auroras occur when energetic particles, often from the sun, are caught in a planet's magnetic field and collide with the upper atmosphere, releasing energy which creates a glow.
Neptune's auroras were previously hinted at during NASA's Voyager 2 flyby in 1989, but have remained elusive to astronomers, unlike successful detections on Jupiter, Saturn, and Uranus.
The James Webb Space Telescope, launched in December 2021, has now made these sightings possible.
Neptune's auroras as captured by the Hubble Space Telescope and James Webb Space Telescope (Image: Space Telescope Science Institute Office of Public Outreach)
The telescope's infrared capability allowed it to capture images of Neptune's auroras and a surprising temperature change over the past 30 years.
Details of these findings were published in the journal Nature Astronomy.
Dr Henrik Melin, a researcher at Northumbria University, said: "It turns out, actually imaging the auroral activity on Neptune was only possible with Webb's near-infrared sensitivity.
"It was so stunning to not just see the auroras, but the detail and clarity of the signature really shocked me."
In addition to imaging the auroras, researchers also characterised the planet's upper atmosphere.
An illustration of the Webb telescope showing the segmented mirror and layered sunshield (Image: Northumbria University)
They found an emission line indicating trihydrogen cation (H3+), which can be created in auroras.
In Webb's images of Neptune, the glowing auroras appear as splotches of cyan.
Heidi Hammel of the Association of Universities for Research in Astronomy, said: "H3+ has been a clear signifier on all the gas giants – Jupiter, Saturn, and Uranus – of auroral activity, and we expected to see the same on Neptune as we investigated the planet over the years with the best ground-based facilities available.
"Only with a machine like Webb have we finally gotten that confirmation."
Neptune's auroras are different from those on Earth, Jupiter, or Saturn.
Instead of being confined to the poles, Neptune's auroras are located at the geographic mid-latitudes due to its unusual magnetic field, which is tilted by 47 degrees from the planet's rotation axis.
The detection of Neptune's auroras will aid understanding of how the planet's magnetic field interacts with particles from the sun.
The team also measured the temperature of Neptune's upper atmosphere for the first time since 1989.
Dr Melin said: "I was astonished — Neptune's upper atmosphere has cooled by several hundreds of degrees.
"In fact, the temperature in 2023 was just over half of that in 1989."
This colder temperature suggests why Neptune's auroras have remained undetected for so long as it would result in much fainter auroras.
This cooling suggests that the region of the atmosphere can change greatly despite the planet's distance from the Sun.
Astronomers now hope to study Neptune over a full solar cycle, which can provide insights into the origin of Neptune's tilted magnetic field.
Leigh Fletcher, co-author of the paper and a researcher at Leicester University, said: "As we look ahead and dream of future missions to Uranus and Neptune, we now know how important it will be to have instruments tuned to the wavelengths of infrared light to continue to study the auroras.
"This observatory has finally opened the window onto this last, previously hidden ionosphere of the giant planets."
