Webb Maps Neptune Auroras After 35 Years, Detects H3+ in Cooler Atmosphere

2 articles · Updated · spacedaily.com · May 26

June 2023 Webb observations have delivered the first clear map of Neptune’s auroras, confirming them through detection of trihydrogen cation, H3+, in the planet’s upper atmosphere.
Several-hundred-degree cooling since Voyager 2’s 1989 measurement helps explain why the signal long eluded Earth-based searches: colder upper-atmosphere gas glows more faintly in the infrared.
Neptune’s magnetic field—tilted about 47 degrees from its rotation axis and offset from the planet’s center—pushes auroral ovals away from the geographic poles and toward mid-latitudes.
That geometry, combined with faint emissions and older instrument limits, helps explain why Voyager 2 saw only indirect auroral signatures rather than the mapped ovals Webb has now resolved.
The result closes a three-decade gap in planetary science, but repeat Webb observations would be needed to tell whether the temperature drop reflects a long-term trend, seasonal change, or something else.

Sources

spacedaily.com19d ago

Webb Telescope Confirms and Maps Neptune's Auroras, Detects H3+ and Cooler Atmosphere

Facebook19d ago

🌌 After decades of mystery, Neptune's hidden auroras have finally been revealed. Using the incredible infrared vision of the James Webb Space Telescope, astronomers captured the first direct images of glowing auroras

Webb solved Neptune's aurora mystery, but uncovered a bigger one: Why is the ice giant's atmosphere rapidly getting colder?

Neptune’s auroras aren't at its poles. Could this mean many distant exoplanets lack the magnetic shields necessary for life?

Completing the Giant Planet Auroral Set: JWST Unveils Neptune’s Auroras and Unexpected Atmospheric Cooling

Overview

In June 2023, the James Webb Space Telescope (JWST) made history by confirming auroras on Neptune for the first time, completing the set of auroral detections for all four giant planets. Using its advanced infrared capabilities, JWST directly imaged bright auroral activity as distinct cyan splotches and detected the trihydrogen cation (H₃⁺) emission line, a key marker of energetic particle precipitation in Neptune’s atmosphere. This discovery provides unprecedented insights into Neptune’s magnetic field and atmospheric dynamics, revealing how energetic particles excite hydrogen molecules to form H₃⁺, which then emits light, making Neptune’s hidden auroras visible at last.

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