Earth's magnetic field is changing
Observing fluid motions in core could
help scientists predict future changes
By Jeremy Hsu
innermost part of the earth. The outer core extends
from 2500 to 3500 miles below the earth's surface
and is liquid metal. The inner core is the central
500 miles and is solid metal.
Something beneath the surface is changing Earth's
protective magnetic field, which may leave satellites
and other space assets vulnerable to high-energy
The gradual weakening of the overall magnetic
field can take hundreds and even thousands of
years. But smaller, more rapid fluctuations within
months may leave satellites unprotected and catch
scientists off guard, new research finds.
A new model uses satellite data from the past
nine years to show how sudden fluid motions within
the Earth's core can alter the magnetic envelope
around our planet. This represents the first time
that researchers have been able to detect such
rapid magnetic field changes taking place over
just a few months.
"There are these changes in the South Atlantic,
an area where the magnetic field has the smallest
envelope at one third [of what is] normal,"
said Mioara Mandea, a geophysicist at the GFZ
German Research Center for Geosciences in Potsdam,
Even before the newly detected changes, the South
Atlantic Anomaly represented a weak spot in the
magnetic field — a dent in Earth's protective
The Earth's magnetic field extends about 36,000
miles into space, generated from the spinning
effect of the electrically-conductive core that
acts something like a giant electromagnet. The
field creates a tear-drop shaped bubble that has
constantly shielded life on Earth against much
of the high-energy radiation flowing from the
The last major change in the field took place
some 780,000 years ago during a magnetic reversal,
although such reversals seem to occur more often
on average. A flip in the north and south poles
typically involves a weakening in the magnetic
field, followed by a period of rapid recovery
and reorganization of opposite polarity.
Some studies in recent years have suggested the
next reversal might be imminent, but the jury
is out on that question.
Measuring interactions between the magnetic field
and the molten iron core 1,864 miles down has
proven difficult in the past, but the constant
observations of satellites such as CHAMP and Orsted
have begun to bring the picture into focus.
Mandea worked with Nils Olsen, a geophysicist
at the University of Copenhagen in Denmark, to
create a model of the fluid core that fits with
the magnetic field changes detected by the satellites.
However, the rapid weakening of the magnetic
field in the South Atlantic Anomaly region could
signal future troubles for such satellites. Radiation
storms from the sun could fry electronic equipment
on satellites that suddenly lacked the protective
cover of a rapidly changing magnetic field.
"For satellites, this could be a problem,"
Mandea told SPACE.com. "If there are magnetic
storms and high-energy particles coming from the
sun, the satellites could be affected and their
connections could be lost."
The constant radiation bombardment from the sun
blows with the solar wind to Earth, where it flows
against and around the magnetic field. The effect
creates the tear-drop shaped magnetosphere bubble,
but even the powerful field cannot keep out all
the high-energy particles.
A large sunspot set off a major radiation storm
in 2006 that temporarily blinded some sun-watching
satellites. Astronauts on the International Space
Station retreated to a protected area as a precaution
to avoid unnecessary radiation exposure.
The Earth's overall magnetic field has weakened
at least 10 percent over the past 150 years, which
could also point to an upcoming field reversal.
Mandea and Olsen hope to continue refining their
model with updated observations, and perhaps to
eventually help predict future changes in the
Earth's magnetic field.
The study was detailed in the May online edition
of the journal Nature Geoscience.
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