 The magnetic field lines point away from Jupiter above the sheet and towards Jupiter below it.The load of plasma from Io greatly expands the size of the Jovian magnetosphere, because the magnetodisk creates an additional internal pressure which balances the pressure of the solar wind.In the absence of Io the distance from the planet to the magnetopause at the subsolar point would be no more than 42 "R"J, whereas it is actually 75 "R"J on average.