Europa's FUV auroral tail on Jupiter

Abstract

Ultraviolet images of Jupiter's northern aurora obtained in 2005 confirm the existence of an electromagnetic interaction between Europa and the Jovian ionosphere. The auroral signature shows a two-component structure: a quasi-circular Europa spot, followed by a previously undetected faint tail emission trailing in the direction of corotation flow. The characteristic brightness for the auroral spot is ~14 +/- 1 kR above background, and approximately 7 +/- 1 kR for the tail. The spot's size is ~1100 km, magnetically mapping to an interaction region <=15 Europa diameters. The auroral tail extends over ~5000 km, which maps along a region of at least 70 Europa diameters. The ultraviolet power emitted by both components varies from a fraction to several GW. The present study suggests auroral interaction at Europa similar to that at Io, but scaled-down by an order of magnitude, including a sub-corotating plasma plume in the geometrical wake of Europa.