We develop a 2-D model for the standing slow-mode expansion fan that is expected to exist downstream of the Jovian moon Io. The leading edge of the expansion fan makes an angle of 45¿ with the upstream magnetic field direction, and the fan width is about 114¿. The plasma flow returns to its upstream direction by way of a slow-mode shock behind Io where the MHD parameters return asymptotically to their upstream conditions. The magnetic field perturbation within the fan is much smaller than that associated with the Alfv¿n wing, which lies farther upstream. ¿ American Geophysical Union 1991