Spinning Earth drags space

Our rotating planet’s tug on space-time, known as frame dragging, takes place almost exactly as specified by relativity theory, report Ignazio Ciufolini of the University of Lecce in Italy and Erricos C. Pavlis of the University of Maryland in Baltimore in the Oct. 21 Nature.

The theory predicts that the two satellites LAGEOS and LAGEOS2 should be dragged about 2 meters in the direction of Earth’s rotation as they orbit. Using 11 years’ measurements from laser beams bounced off the satellites, Ciufolini and Pavlis found 99 percent of the expected orbital shift. “This is the first accurate measurement” of frame dragging, claims Ciufolini.

Until recently, measurements of gravity variations around the world had lacked accuracy, fueling distrust of frame-dragging results based on those numbers. This latest measurement is “much more convincing,” says Neil Ashby of the University of Colorado in Boulder.

Still, skepticism about the laser method lingers, especially from researchers associated with a space experiment known as Gravity Probe B (SN: 9/25/04, p. 206: Available to subscribers at Orbiting relativity test gets slow start). Using a gyroscope-based technique, that mission is expected to report by 2006 a frame-dragging result at least 10 times more precise than the latest finding.

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