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This figure shows a model of the Earth's magnetic field being generated within the Earth.
Click on image for full size
Gary A Glatzmaier (Los Alamos National Laboratory) and Paul H Roberts (University of California, Los Angeles).

Generating a Magnetic Field

Scientists believe there are two essential ingredients for generating a magnetic field. Those two ingredients are

A bar of iron can be made into a magnet by wrapping it with wires and running a current through the wires.

It is thought a planet, or a star, can generate a magnetic field if it has both of the two ingredients above. It must have enough magnetic material, and it must have currents moving inside the magnetic material. If a planet does not have enough of either of these two ingredients, it will not have a magnetic field. Planets which do not have magnetic fields include Venus (moves very slowly), and Mars (most the iron is on the surface, and not molten).

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Earth's Magnetic Poles

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The Magnetic Poles of Mercury

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Planetary Magnets

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A magnetometer is an instrument for measuring magnetic fields. Many spacecraft carry magnetometers to measure the magnetic fields around planets. When a spacecraft makes those measurements, what do the...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA