Webb Detects Neptune Auroras, Finds Upper Atmosphere Near 358K vs Voyager’s 750K
Updated
Updated · spacedaily.com · Aug 23
Webb Detects Neptune Auroras, Finds Upper Atmosphere Near 358K vs Voyager’s 750K
3 articles · Updated · spacedaily.com · Aug 23
Summary
358 kelvin—plus or minus 8—was the upper-atmosphere temperature Webb derived from Neptune’s June 2023 spectra, far below Voyager 2’s roughly 750 kelvin estimate from 1989 and leaving scientists without a full explanation.
H3+ emission gave Webb the first definitive auroral detection on Neptune, confirming charged-particle activity that earlier observations had only hinted at.
Southern mid-latitude auroral hotspots matched Neptune’s unusually tilted, off-center magnetic field, which channels particles away from a simple polar-cap pattern.
The colder ionosphere also helps explain why decades of ground-based searches missed Neptune’s H3+ signal: at about 358 kelvin, the molecule radiates much more weakly in infrared.
34 years between the two measurements span nearly a Neptunian season, but researchers say seasonality, solar wind, atmospheric waves and chemistry all remain possible drivers that repeated Webb observations must test.