The Distorted Shape of Jupiter's North Auroral Oval - A Possible Magnetic Anomaly

Repeated imaging of Jupiter's aurora has shown that the northern main oval has a distorted "kidney bean" shape in the general range of 40-100 deg magnetic longitude, which appears unchanged since 1994. More recently, improved accuracy in locating the satellite footprint auroral emissions has provided new information about the geometry of Jupiter's magnetic field in this and other areas. The persistent pattern of the main oval implies a disturbance of the local magnetic field, and the increased latitudinal separation of the locus of satellite footprints from each other and from the main oval implies a locally weaker field strength. It is possible that these phenomena result from a magnetic anomaly in Jupiter's intrinsic magnetic field, as was proposed by A. Dessler in the 1970's. There is presently only limited evidence from the scarcity of auroral footprints observed in this longitude range. Similarly, while it is difficult to observe the conjugate regions in the southern aurora, there does not appear to be any corresponding distortion in the south. We will present the observational evidence that we have accumulated to date, propose future observations to determine the nature of this disturbance, and speculate on its causes and implications.