The Webb Space Telescope has given us our first glimpse of Neptune glowing with bright auroras, a visually stunning phenomenon that has long evaded scientists studying the ice giant.
Using Webb’s near-infrared spectrograph, astronomers have captured new images of Neptune that finally reveal the planet’s mysterious auroral activity. Faint hints of Neptune’s auroras were first detected during Voyager 2’s flyby of the planet, but Webb’s latest discovery is the first direct evidence of the phenomenon.
“Turns out, actually imaging the auroral activity on Neptune was only possible with Webb’s near-infrared sensitivity,” Henrik Melin, a researcher at Northumbria University and lead author of a new paper published in the journal Nature Astronomy, said in a statement. “It was so stunning to not just see the auroras, but the detail and clarity of the signature really shocked me.”
Neptune lies on the outer edges of the solar system, around 3 billion miles (4.8 billion kilometers) away from the Sun. At such great distance, it’s proven difficult to visit the farthest planet and be able to observe it up close. The famous interstellar probe, Voyager 2, was the only spacecraft to do so in 1989, revealing Neptune’s atmosphere, rings, and moons. Voyager 2 also revealed that the ice giant has auroras—magnetically induced displays that light up the skies when charged particles interact with the planet’s atmosphere.
Scientists collected the first evidence of auroras beyond Earth in the 1970s through the Pioneer and Voyager missions, which detected hints of auroras on Jupiter, Saturn, Uranus, and Neptune. Since then, Neptune has remained the only planet not to have direct evidence of its auroras. With Webb’s latest images, scientists finally have the full picture of auroral activity throughout the solar system.
Scientists obtained the data in June 2023, using it to characterize the composition and measure the temperature of the planet’s upper atmosphere. They also noticed something odd about Neptune’s auroras. Unlike on other planets, in which the auroras are confined to the northern and southern poles, Neptune’s auroral activity takes place at the planet’s geographic mid-latitudes (around where South America is on Earth).
This is caused by Neptune’s unique magnetic field, which is tilted by 47 degrees from the planet’s rotation axis, according to the study. Since auroral activity is located around where a planet’s magnetic field meets its atmosphere, Neptune’s auroras are far from its rotational poles.
“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,” Leigh Fletcher, a planetary scientist from the University of Leicester and co-author on the paper, said in a statement. “This observatory has finally opened the window onto this last, previously hidden ionosphere of the giant planets.”
