For those with electronic access to Science, reprints are available through Science Online . Since this emission is visible across the entire slit, we see an image of the slit at this wavelength. Note that there are peaks in the emission at the position of Io at many of the wavelengths in the image.
Additional views are available here and here .
In the second sequence, a wireframe representation has been overlaid at the calculated position of Io. The direction of the magnetic field at Io also changes as a result of this wobbling motion. It appears that the bright regions of oxygen and sulfur emission near Io's equator move in response to changes in the superimposed magnetic field, and are located in a plane roughly perpendicular to the field direction. There must certainly be perturbations introduced by local variations in the magnetic field, created by electric currents flowing along magnetic field lines and through Io's ionosphere. These phenomena are currently under investigation.