I'm trying to get a feel for the overall magnitude of the Earth's magnetic field. If I placed a superconducting belt around the Earth magnetic equator, how much current would that loop have to carry to approximate the Earth magnetic field? Currently, the field at the equator is about 31 microT and at 50 degrees latitude is about 58 microT. If I replace the Earth with a vacuum, it looks like I would need on the order of 20MA - but I have no confidence in that estimate. It looks to me as though the Earth's iron content might bring this number down.