The Earth is a good example of a planetary dipole, where the lines of force point in a direction out of the South (magnetic) Pole and into the North (magnetic) Pole. Planets can also show evidence of quadrupoles (4 poles) and octupoles (8-poles).
Not every planet has a magnetic field. It takes special conditions to make a magnetic field within a planet. Other planets known to have a magnetosphere include Mercury, Mars (perhaps), Jupiter, Saturn, Uranus, and Neptune. Venus is special case of a rocky planet with no magnetic field.
source : windows to the universe