Mars magnetosphere?

Question

ok this has been bugging me for a while now. if supposedly venus, earth, and mars had/have a molten core then why is earth the only one with a magnetic field. does it have something to do with plate tectonics and the moon.

Answer 1

Actually, Venus is the only one WITHOUT a magnetic field.  

Mars may have a magnetic field.  

But Earth, Mercury, Jupiter, Saturn, Uranus and Neptune all have magnetic fields.  

*below is copied and pasted from source link  

Scientists believe, although it is not certain, there are two essential ingredients for generating a magnetic field. Those two ingredients are

magnetic material

currents

A bar of iron can be made into a magnet by wrapping it with wires and running a current through the wires.

It is believed that a planet, or a star, can generate a magnetic field if it has both of the two ingredients above. It must have enough magnetic material, and it must have currents moving inside the magnetic material. If a planet does not have enough of either of these two ingredients, it will not have a magnetic field. Planets which do not have magnetic fields include Venus (moves very slowly), and Mars (most the iron is on the surface, and not molten).

Answer 2

Earth's core rotates relative to the surface, making its field much stronger, although I'm not sure how that works or if the Moon is responsible.

Answer 3

Earth is the only terrestrial planet with a significant magnetic field because it is the only one that has all the ingredients: a conducting liquid, convection, and rotation.

Venus, because of its lack of plate tectonics, lacks convection.  Mars lacks a conducting liquid because its core solidified.