Geophysicists have noted that the strength of Earth’s magnetic field has been decaying-about 5 percent globally over the past century. Though the colors in the second image are just as bright as the first, note that the greatest changes were plus or minus 100 nanotesla in a field that reaches 60,000 nanotesla. The second image shows changes in that field over the same period. It also provides the basis for navigation with a compass.īased on data from Swarm, the top image shows the average strength of Earth’s magnetic field at the surface (measured in nanotesla) between January 1 and June 30, 2014. Generated by the motion of molten iron in Earth’s core, the magnetic field protects our planet from cosmic radiation and from the charged particles emitted by our Sun. Launched in November 2013 by the European Space Agency (ESA), the three-satellite Swarm constellation is providing new insights into the workings of Earth’s global magnetic field.
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