Question

What are the 3 conditions for a planet to have a global magnetic field?  Explain why Mars and Venus have or do not have a global magnetic field  based on those conditions.

Answer 1

Three basic conditions to have global magnetic field.

1) Earth's core is filled with molten metal which makes it a region with electrically conducting fluid. As we know a conductor with electricitiy will have magnetic field set up around it.

2) The rotation of the planet. It must be fast.

3) Convection in the layer fluid.

Mars and venus doesn't have strong magnetic field because for venus,  because of its slow rotation (243 days) and its predicted lack of internal thermal convection, any liquid metallic portion of its core.

In case of mars, the liquified core solidifies too early due to cooler temperarature.s.