PLANETS
Do all planets have magnetic fields?
Earth’s poles are a consequence of its magnetic field
The magnetic field of a planet is generated by fluid motions in an electrically conducting region of its interior; without such motions, or if they are not vigorous enough, a planet will not have a magnetic field. For Earth, this region is the liquid outer core, which is dominantly composed of iron and nickel. Heat escaping the core powers turbulent convective flows. In a good electrical conductor, magnetic field lines tend to remain attached to material particles. These flows can twist and shear an existing magnetic field, and this is the process that can sustain it. Take away this stirring, and the field decays. For Earth, this would take about 30,000 years.