Detection of the infrared aurora at Uranus with Keck-NIRSPEC

Near-infrared (NIR)-wavelength observations of Uranus have been unable to locate any infrared aurorae, despite many attempts to do so since the 1990s. While at Jupiter and Saturn, NIR investigations have redefined our understanding of magnetosphere–ionosphere–thermosphere coupling, the lack of NIR auroral detection at Uranus means that we have lacked a window through which to study these processes at Uranus. Here we present NIR Uranian observations with the Keck II telescope taken on the 5 September 2006 and detect enhanced H 3 + emissions. Analysing temperatures and column densities, we identify an 88% increase in localized H 3 + column density, with no significant temperature increases, consistent with auroral activity generating increased ionization. By comparing these structures against the Q 3 mp magnetic-field model and the Voyager 2 ultraviolet observations, we suggest that these regions make up sections of the northern aurora.