The Webb Space Telescope has allowed us to see Neptune glowing with bright auroras for the first time – a visually stunning phenomenon that has long eluded scientists studying the icy giant.
Using the Webb Near-Infrared Spectrograph, astronomers have obtained new images of Neptune that finally reveal the planet’s mysterious auroral activity. Faint hints of Neptune’s aurorae were first detected during Voyager 2’s flyby of the planet, but Webb’s latest discovery is the first direct evidence of the phenomenon.
“It turns out that it was really only Webb’s near-infrared sensitivity that allowed us to image the auroral activity on Neptune,” said Henrik Melin, a researcher at Northumbria University and lead author of the new paper published in the journal Nature Astronomy. “It was so stunning that not only did I see the aurorae, but the detail and clarity of the signature really shocked me.”
Neptune lies at the outer edge of the solar system, about 3 billion miles (4.8 billion kilometers) from the Sun. At such a great distance, it proved difficult to visit the most distant planet and observe it up close. The famous Voyager 2 interstellar probe was the only spacecraft to do so in 1989, discovering Neptune’s atmosphere, rings, and moons. Voyager 2 also discovered that the icy giant has auroras, magnetically induced displays that light up the sky when charged particles interact with the planet’s atmosphere.
The first evidence of auroras beyond Earth was gathered in the 1970s by the Pioneer and Voyager missions, which found hints of auroras on Jupiter, Saturn, Uranus, and Neptune. Since then, Neptune has remained the only planet without direct evidence of aurorae. With Webb’s latest images, scientists finally have a complete picture of auroral activity throughout the solar system.
Scientists received 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 strange about Neptune’s aurorae. Unlike other planets, where auroras are confined to the north and south poles, Neptune’s aurorae occur in the geographic middle latitudes of the planet (roughly where South America is located on Earth).
According to the study, this is due to Neptune’s unique magnetic field, which is tilted 47 degrees from the planet’s rotation axis. Since auroras are centered around the place where a planet’s magnetic field meets its atmosphere, Neptune’s aurorae are far from its rotation poles.
“As we look to the future and dream of future missions to Uranus and Neptune, we now know how important it is to have instruments tuned to infrared wavelengths to continue to study the aurorae,” said Lee Fletcher, a planetary scientist at the University of Leicester and co-author of the paper, “We have finally opened a window into a recent but very important chapter in history. “This observatory has finally opened a window into the last, previously hidden ionosphere of the giant planets.”
