EARTH'S INNER CORE MAY ROTATE FASTER THAN REST OF PLANET, SCIENTISTS SAY.

Byline: William J. Broad The New York Times

Scientists Wednesday reported finding strong evidence that the Earth's inner core is spinning freely and slightly faster than the rest of Earth, making it virtually a planet within a planet.

The scientists, at Columbia University, said the inner core was moving fast enough to lap the surface once every 400 years or so.

Such inner freedom has never been reported before for any rocky body or planet in the cosmos.

The discovery is expected to advance knowledge of how heat flows through Earth, how its interior evolved over the ages, and how its magnetic field forms and periodically reverses.

Earth's inner core is a solid mass of blisteringly hot iron 1,500 miles wide, roughly the distance between New York and Dallas, making it slightly smaller than the moon. The inner core is very difficult to study because of its remoteness, but recent advances in seismic measurement and computer modeling are beginning to unveil some of its secrets.

Scientists have speculated for more than a decade that the inner core might spin independently of the rest of the planet and recently predicted it in some detail. But evidence was lacking.

The discovery was reported by Dr. Xiaodong Song and Dr. Paul Richards, seismologists at Columbia's Lamont-Doherty Earth Observatory in Palisades, N.Y. Their findings were announced Wednesday at a news conference in New York City and appear today in the journal Nature.

A team based at Harvard University has also found evidence of the core's independent spin and has submitted a paper to the journal Science.

``It's quite remarkable,'' Dr. David Stevenson, a planetary scientist at the California Institute of Technology in Pasadena, said of the twin findings in an interview. ``We've never had information about motions near the center of the Earth. It's one of those things that we didn't expect to get.''

Dr. Gary Glatzmaier, a geophysicist at the Los Alamos National Laboratory in New Mexico, said: ``It's a breakthrough. It's the beginning of a new field.

``In the past,'' he continued, ``people thought changes in the interior of the Earth were very slow. Now we can see something changing on a time scale of 10 years. That's remarkable.''

The reported speed of the independent rotation is lightning fast compared with many geological movements, which tend to occur over millenniums.

The Columbia team estimates that the speed of the core's independent spin is between 0.4 and 1.8 degrees per year. With 360 degrees in a circle, that equals roughly one lap every 400 years.

Dr. Adam Dziewonski, leader of the Harvard team, which also has a member at the University of California, Berkeley, said it had found evidence of a spin rate up to 3 degrees per year, which yields a lap every 100 years or so.

``If astronomers picked up something like this they would send a satellite,'' Dziewonski said of the independent spin in an interview. ``We need more seismic stations and better computers.''

Scientists say the independent motion is most likely caused by the inner core's interaction with powerful magnetic fields generated by moving fluids in Earth's outer core, which is molten. These fields are thought to create a torque that makes the core spin faster, much as the moving magnetic fields in an electric motor cause its armature to turn.

Moreover, the low viscosity, or low internal friction, of material in the outer core makes it ``easy for the inner core to rotate,'' the Columbia team said in its Nature paper.

The finding, the team added, raises many questions, such as whether the rate of rotation ever changes and whether the spin produces observable fluctuations in the strength of the gravitational field at the Earth's surface.

``This is just the beginning,'' Richards of Columbia said in an interview. ``There've been hundreds of fine theory papers. But now there's a hard observation to hang the theory on.''

By weight, the Earth is mostly iron. Four and a half billion years ago, during the planet's fiery birth, most of that iron sank into the planet's deep interior because of its enormous weight and eventually formed inner and outer cores.

The outer core is molten iron. Deeper still, pressures and densities become so monumental that the iron is solid despite temperatures believed to be above 7,000 degrees Fahrenheit. This solid inner core makes up less than 1 percent of the Earth's volume. Since its discovery 60 years ago, scientists have usually considered it obscure, featureless and having little or no observable impact on the planet.

The main way of studying this remote domain is with sensors that pick up faint vibrations in the ground, which let scientists map the paths and speeds of shock waves that radiate out from big earthquakes and explosions the way ripples move across a pond.