By Jeremy Hsu, Staff Writer
posted: 18 August 2008 06:35 am ET
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- The 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. Credit: John Lahr, USGS Open-File Report 99-132
- The solar wind is a continuous flow of particles from the Sun consisting of electrically charged particles in a state known as plasma. The Earth’s magnetic field is distorted by the solar wind to a droplet-shaped magnetic bubble called the magnetosphere. On the nightside, the Earth’s magnetic field is stretched into a long tail, the magnetotail, much like the tail of a comet. The blue cavity represents the magnetosphere. The red area denotes the region where a large amount of charged particles reside and intense electric currents flow within the magnetosphere. The four Cluster satellites encountered a flow reversal region in the magnetotail. Credit: Tony Lui, JHU/APL
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 the high-energy radiation flowing from the sun.
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 (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 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.
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.
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