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 electric currents create a magnetic field. So every change in the flow of
the 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.”
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