Our first encounter with Aurora on Neptune

For the first time, researchers discovered infrared aurora swirling in Neptune’s atmosphere, examining decades of scientific speculation.

When NASA’s Voyager 2 mission was flew by Neptune in 1989, I found an appetizing hint of aurora activity in the clouds of Ice Giant. However, scientists were unable to verify the phenomenon at the time because existing equipment was too weak. Now, James Webb Space Telescope (JWST) has finally provided the power to detect them.

“This really was a fulfillment of long-standing expectations.” Heidi Hammel Washington, DC, Astronomical Research Association.

Hammel and her colleagues used NirSpec from JWST, a powerful infrared imaging tool, to capture spectral images of Neptune and analyze light at various wavelengths emitted by the planet. In 2023, researchers used musical instruments to detect Uranus’ infrared aurora. This time I found it on Neptune too.

The images allowed Hammel and her team to begin building a map of Neptune’s magnetic field. This is particularly exciting as the planet is known to have some of the rarest magnetic poles in the solar system.

Unlike Earth, Jupiter, and Saturn, Neptune’s magnetic poles are not at the center of their rotating poles. Instead, “they are offset by almost half the planet’s radius,” says Hammel. As a result, the aurora appears as an irregular mass far closer to the equator.

In addition to detection of Auroras, observations of JWST showed that the ionosphere of Neptune, a layer of charged particles that covers several planets, was cooled. Now, on average, it’s about 10% colder than when the Voyager 2 passed 34 years ago. A similar change was detected on Uranus.

The authors of the new study are unclear why this cooling occurred, but they hope that the upcoming JWST observation period, scheduled for 2026, will provide more clues.