How does a planet get a magnetic field?

Many planets generate magnetism through a dynamo process in their interiors. In Earth’s case, the motion of molten iron in the outer core, combined with rotation, produces the magnetic field that helps shield the planet from solar wind. Jupiter’s field likely comes from electrical currents in metallic hydrogen deep inside the planet, while Mercury’s weaker field probably comes from a partially molten iron core. Planets without an active dynamo, like Mars today, have lost most of their global magnetic field. Magnetic fields are important because they can protect atmospheres and influence space weather.