ABOUT MAGNETOMETERS: These are instruments used to measure the strength and orientation of a magnetic field. They can be used in planet-exploring spacecraft -- to measure the magnetic field of Earth and other bodies in space--or to help detect the magnetic components of explosive devices. Most types of magnetometer depend on the relationship between magnetism and electricity. The sensors convert the magnetic field into an electrical current that can be measured, explaining the size and direction of the magnetic field.
WHAT MAKES MATERIALS MAGNETIC? Magnetism is the result of the constant movement of charged electrons in atoms. As electrons swirl around an atom, they create an electrical current, and whenever electricity moves in a current, a magnetic field is created. So magnetism is a force between electric currents: two currents flowing in the same direction attract each other, while those pulling in opposite directions repel each other. The reason some materials are magnetic, while others are not, has to do with how the electrons are arranged. A magnet is an object made of magnetic materials; naturally occurring magnets are known as lodestones. Every magnet has at least one north pole and one south pole. In fact, if you take a bar magnet and break it into two pieces, each of the smaller pieces will still have a north and south pole. The Earth itself is a giant magnet with a north and south pole, which is why the needle of a magnetic compass always points north/south.