An electrical current produces a magnetic field. Movement of a metallic liquid will generate an electrical current. A planet's iron core will produce an electrical current as the planet rotates if the core is molten. Mars's core is solid iron. Yet, Mars has a very weak magnetic field. It is over 10,000 times weaker than Earth's. Perhaps the core was molten in the planet's early history. The weak magnetic field that Mars has now may be left over from the period billions of years ago when the core was molten.
