  We analyze the ionization state of the magnetohydrodynamically turbulent
protoplanetary disks and propose a new mechanism of sustaining ionization.
First, we show that in the quasi-steady state of turbulence driven by
magnetorotational instability in a typical protoplanetary disk with dust
grains, the amount of energy dissipation should be sufficient for providing the
ionization energy that is required for activating magnetorotational
instability. Second, we show that in the disk with dust grains the energetic
electrons that compose electric currents in weakly ionized gas can provide
collisional ionization, depending on the actual saturation state of
magnetorotational turbulence. On the other hand, we show that in the
protoplanetary disks with the reduced effect of dust grains, the turbulent
motion can homogenize the ionization degree, leading to the activation of
magnetorotational instability even in the absence of other ionization
processes. The results in this Letter indicate that most of the regions in
protoplanetary disks remain magnetically active, and we thus require a change
in the theoretical modeling of planet formation.
