 These radial currents are also the source of the magnetic field's azimuthal component, which as a result bends back against the rotation.The particle number density of the plasma decreases from around 2,000 cm−3 in the Io torus to about 0.2 cm−3 at a distance of 35 "R"J.In the middle magnetosphere, at distances greater than 10 "R"J from Jupiter, co-rotation gradually breaks down and the plasma begins to rotate more slowly than the planet.