Measuring Earth’s Magnetism

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. 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. It also provides the basis for navigation with a compass.

Based 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. The second image shows changes in that field over the same period. 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, a minuscule but still detectable change in a field that reaches 60,000 nanotesla.

Geophysicists have noted that the strength of Earth’s magnetic field has been decaying—about 5 percent globally over the past century. However, it is not changing in a uniform way; it grows growing stronger in some places and weaker in others.

The changes are a natural variation due to processes in the deep interior of the Earth, explained Nils Olsen, a Swarm team member from the Technical University of Denmark. The movement of molten iron in the core creates electric currents, and changing electric currents create a magnetic field. So every change in the flow of the iron core means changes in the magnetic field.

“The magnetic field changes in a chaotic manner, and we do not know why it changes in the way it does nor how it will evolve in the future,” said Olsen. “There is no periodic behavior, and it is therefore rather difficult, if not impossible, to predict how the magnetic field evolves over time. We can just observe how it has changed in past and what it looks like today.”

1. References

2. European Space Agency (2014, June 19) Swarm Reveals Earth’s Changing Magnetism. Accessed September 5, 2014.
3. NASA Earth Observatory (2011, April 23) Earth’s Magnetosphere.
4. NASA Earth Observatory (2004, May 22) Earth’s Surface Magnetism.
5. NASA Earth Observatory (2004, March 30) Gravity Recovery and Climate Experiment.

Images and video courtesy of European Space Agency/Technical University of Denmark (ESA/DTU Space). Caption by Mike Carlowicz, based in part on a story from the European Space Agency.

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Model - NASA