The Pioneer Venus magnetic field measurements have suggested the possibility of a different type of interaction between the solar wind and the ionosphere of a non-magnetized planet than has been envisioned in the past. An unexpected aspect of the observations is that the magnetic field of the shocked solar wind does not penetrate the ionosphere; thus it appears that the ionosphere acts approximately as a superconductor, excluding any substantial penetration of interplanetary magnetic field. The ionosphere on the day side is terminated sharply at an ionopause and is magnetized weakly or not at all. Just beyond the ionopause is a magnetized region with relatively little plasma, and whose magnetic pressure is approximately equal to the impact pressure of the solar wind. This suggests to us the possibility of an interaction where the current system associated with the region of enhanced magnetic field flows along the ionopause and is closed by currents in the shocked solar wind plasma, where the J¿¿B¿ forces act to slow down the plasma approaching the stagnation region and accelerate the plasma flowing away from it. With this concept, the lack of magnetic constraint in the ionosphere would allow ionospheric plasma to flow freely from the day to the night side and this flow, whose magnitude should depend inversely on the solar wind pressure, would probably maintain the nighttime ionosphere.