NASA satellites use very sensitive devices called magnetometers to measure the magnetic fields of planets. Like very sensitive compasses, these devices can measure both direction and strength of planetary magnetic fields.
This animation shows how a magnetometer is used on a satellite to measure a planetary magnetic field.
This silent animation depicts how a fluxgate magnetometer works.
This animation decpicts how three fluxgate magnetometers can be used to get a three-dimensional measurement of a magnetic field.
This animation shows how iron filings can be used to reveal the magnetic field around a bar magnet. It also shows how a compass can be used to infer the magnetic field around the magnet.
Please give credit for this item to:
NASA/Goddard Space Flight Center