First Measurement of Earth's Inner Magnetism Made
Tuesday, December 28, 2010 The northern lights hang along the planet's magnetic field. For the first time, scientists have measured the strength of the field in Earth's core.
Credit: NASA

For the first time ever, a scientist has measured the strength of the magnetic field inside Earth's core, some 1,800 miles (2,896 kilometers) underground.

It turns out the magnetic field in Earth's core is about 50 times stronger than on the planet's surface, and the new number may help scientists narrow down the possible heat sources that fuel the mysterious processes of the planet's interior.

"A measurement of the magnetic field tells us what the energy requirements are and what the sources of heat are," said Bruce A. Buffett, a professor of Earth and planetary science at the University of California, Berkeley, who made the measurement.

Scientists think that Earth's heat comes from three sources: the residual heat from the formation of the planet around 4.5 billion years ago, when the planet was hot and molten; the release of gravitational energy as heavy elements sink to the bottom of the liquid core; and the radioactive decay of long-lived elements such as potassium, uranium and thorium.

The cooling Earth originally captured its magnetic field from the planetary disk in which the solar system formed. That field would have disappeared within 10,000 years if not for the planet's internal dynamo, which regenerates the field thanks to heat produced inside the planet.

The heat makes the liquid outer core ? which is about 1,400 miles (2,253 km) thick ? boil, or convect, and as the conducting metals rise and then sink through the existing magnetic field, they create electrical currents that maintain the magnetic field. This roiling dynamo produces a slowly shifting magnetic field at the surface.

Buffet pulled off the geophysics milestone by harnessing the aid of some distant helpers: the moon and quasars ? extremely bright and distant active galaxies.

Quasars hurl from their luminous hearts a steady stream of radio waves that provide a consistent backdrop against which Earth's most minute wigglings are noticeable, and measurements of these radio waves from ground-based and satellite telescopes allow for very precise data on changes in Earth's rotation axis.

By looking at these changes, and how they are affected by the moon's gravitational tug on the Earth, Buffet was able to make his calculations.

"I still find it remarkable that we can look to distant quasars to get insights into the deep interior of our planet," Buffett said.

He's now at work on a second-generation model, and admits that a lack of information about conditions in the Earth's interior has been a big hindrance to making accurate models.

This article was provided by OurAmazingPlanet, a sister site to LiveScience.