Sloshing Inside Earth Changes Protective Magnetic Field
By Jeremy Hsu
Staff Writer
posted: 18 August 2008
06:35 am ET
  Something beneath the surface is changing Earth's protective
magnetic field, which may leave satellites and other space assets vulnerable to
high-energy radiation.
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, Germany.
Even before the newly detected changes, the South Atlantic
Anomaly represented a weak spot in the magnetic field — a dent in Earth's
protective bubble.

Bubble bobble

The Earth's magnetic field extends about 36,000 miles
(58,000 km) 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 thehigh-energy radiation flowing from the sun.
The last major change in the field took place some 780,000
years ago during a magneticreversal, 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 (3,000 km) 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.

Electric storm

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 AtlanticAnomaly 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.

Topsy-turvy history

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.