Chapter 13. Ionization State and Magnetic Fields in the Solar Nebula

The densities of various charged particles in the solar nebula are investigated. The ionization fraction is found to be smaller than 10-10 in most parts of the gaseous nebula. Dust grains with the electric charge e and -e are dominant charged particles in the region of the terrestrial planets. By comparing the dissipation time of magnetic fields with the Keplerian period, the fields are found decoupled from the gas in the region of the terrestrial planets. The fields couple strongly with the gas and their effects on the structure of the nebula may be important only in the region of the giant planets. In the region with the temperature T \gtrsim 1 × 103 K the gas is strongly coupled with magnetic fields because the ionization fraction is enhanced by the thermal ionization of alkali metals.