Is Earth the only planet with a magnetic field?
No, almost every planet and many moons have magnetic fields (though not every moon). The most significant lack of a magnetic field is with our neighbor Venus. Any magnetic field has as of yet been undetectable, though a couple of hits have indicated that it may have a very small field, less than E-5 the strength of Earth’s field. Nearly impossible to detect, and so small that no one can decide whether to even admit that it’s more than a sensor glitch. It is theorized that one large reason for a lack of magnetic field is that it barely rotates on its axis: it has a rotation period of 243 Earth-days.
