NASA's James Webb Space Telescope has successfully captured the aurora borealis on the planet Neptune in spectacular detail for the first time in history.
This fascinating atmospheric phenomenon occurs when charged particles from the Sun collide with gas atoms in the planet's atmosphere, producing enchanting, colorful glows.
For the past few decades, astronomers had managed to capture only fleeting glimpses of auroral activity on Neptune—most notably during a 2 flyby by NASA's Voyager 1989 spacecraft. But unlike its gas giant neighbors like Jupiter, Saturn, and Uranus, Neptune's auroras had remained elusive—until the Webb telescope finally cracked the mystery.
In June 2023, the James Webb Telescope used its near-infrared spectrograph to observe auroras on Neptune with unprecedented precision. In addition to the image of the planet, scientists obtained a spectrum that allowed them to analyze its composition and measure the temperature of the upper atmosphere (ionosphere).
In a groundbreaking discovery, observations revealed strong emission from an ion called H₃⁺ (trihydrogen ion), a molecule well known for its role in auroral phenomena.
Surprisingly, Neptune's auroras are nothing like those seen on Earth, Jupiter, or Saturn. Instead of being concentrated around the poles, as is usually the case, Neptune's lights appear at mid-latitudes—roughly where South America is located on Earth.
Researchers attribute this peculiarity to the strange tilt of Neptune's magnetic field, a phenomenon also discovered by Voyager 2 in 1989.
Another surprise: scientists were able to measure the temperature of Neptune's upper atmosphere for the first time since Voyager 2's passage. And the results were astonishing: it has cooled by several hundred degrees since the last measurement, which could explain why auroras have been so difficult to detect until now.
This breakthrough offers a new way to explore the interaction between Neptune's magnetic field and solar particles reaching the outer reaches of the solar system. The team now plans to observe the planet throughout a full 11-year solar cycle using the James Webb telescope, which could reveal even more secrets about this enigmatic icy planet.
"It wasn't just the sighting of the aurora that was extraordinary," says Henrik Melin of Northumbria University, lead author of the study, "it was the clarity and detail that really blew me away."
The results, published in the journal Nature Astronomy, mark an exciting advance in understanding the atmospheric dynamics of the icy giants in our solar system.
