Observations of Jovian polar auroral filaments

In this paper we report a phenomenon hitherto unobserved in Jupiter's ultraviolet polar auroras, specifically thin (~0.6° wide), long-lived quasi-sun-aligned polar auroral filaments (PAFs) of brightness ~100 kR spanning the highly variable region poleward of the main oval. This observation, made using Hubble Space Telescope images, is significant since no coherent structures have previously been observed in Jupiter's very high latitude auroral region, and it may help shed light on the dynamics of Jupiter's under-explored magnetotail. PAFs have been observed in 4 sets of observations over 6 days in 2007, and their occurrence appears to be independent of impinging solar wind conditions. The feature comprises two components: the section toward noon remains fixed in orientation toward the sun, while the anti-sunward section rotates. We estimate overall rotation rates of ~0--45% of corotation, values which may indicate the rotation rate of Jupiter's polar ionosphere and tail lobes.