Voyager 2 flew past Neptune in 1989 and detected faint hints of auroras it couldn't explain — because the magnetic field is tilted 47 degrees off the rotation axis and the auroras were glowing in enti

Key Points:

• The James Webb Space Telescope (JWST) has provided the first direct evidence of auroras on Neptune by detecting the trihydrogen cation (H3+) in its upper atmosphere, using its Near-Infrared Spectrograph in June 2023.
• Neptune's auroral ovals are located away from the planet's rotational poles due to its magnetic field being tilted about 47 degrees and offset from its center, explaining why earlier searches based on Earth-like assumptions failed to detect clear auroras.
• The study also found Neptune’s upper atmosphere to be several hundred degrees cooler than measurements taken by Voyager 2 in 1989, which contributed to the difficulty in detecting auroral emissions from Earth.
• Voyager 2’s 1989 flyby instruments were limited by sensitivity and assumptions about auroral location, whereas JWST’s infrared capabilities and ability to image the whole planet allowed it to detect faint auroras despite the cooler atmosphere.
• While confirming Neptune’s auroras and refining knowledge of its magnetic field, the findings raise questions about the significant atmospheric cooling observed over three decades, suggesting the need for ongoing observations to understand potential long-term or seasonal changes.