Jupiter’s colorful hair

Abstract

Auroral emissions on Jupiter form intricate structures. They may be conveniently separated by transient and more permanent features. Transient features often appear in the poleward-most sector of the auroral polar region and are usually found to depend on the direction of the Sun. Interestingly, the brightness and morphology of these polar emissions, at least in the north, appear to depend both on local time, but also on the sub-solar longitude. On the other hand, the permanent or longer lifetime auroral emissions are frequently associated with the main and outer emissions and are found to move close to corotation with Jupiter. However, this distinction between transient auroral features that are poleward and fixed in local time, and permanent features that are equatorward and corotating is somewhat artificial and may not include other types of auroral emissions. The dawn storm and the polar bright spot are two examples of such auroral emissions not following this simple categorization. The global morphology of Jupiter’s aurora was largely constrained by observations with HST, which only sees Jupiter’s dayside hemisphere. Thanks to the polar orbit of Juno, we now have access to views of the aurora at all local times and in particular to the night side hemisphere. We have combined HST-STIS, Juno-UVS and Juno-JIRAM observations of Jupiter’s UV and IR aurora to bring forward a new type of auroral structure - Jupiter’s hair - forming long-term multiple arcs whose orientation and location are influenced by local time. They extend from the poleward boundary of the main emission to the polar region, in the afternoon sector. This structure presumably encompasses previously found auroral features like the poleward auroral filament, transpolar arcs, and the auroral bridge structure