  The most remarkable feature of the ultraviolet auroras at Jupiter is the ever
present and almost continuous curtain of bright emissions centered on each
magnetic pole and called the main emissions. According to the classical theory,
it results from an electric current loop transferring momentum from the Jovian
ionosphere to the magnetospheric plasma. However, predictions based on these
mainstream models have been recently challenged by observations from Juno and
the Hubble Space Telescope. Here we review the main contradictory observations,
expose their implications for the theory and discuss promising paths forward.
