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" Building a test planet takes serious engineering. Researchers at the University of Maryland have constructed a 30-ton sphere that spins at more than 90 mph to generate magnetic fields. The 10-ft.-dia. sphere is filled with 13.5 tons of liquid sodium to mimic the Earth&amp;#039;s liquid-iron center core. A 3.3-ft.- dia. stainless-steel sphere inside the larger one counterrotates to approximate the motion of the planet&amp;#039;s solid iron inner core. The action of Earth&amp;#039;s inner liquid produces a magnetic field that makes compasses work, deflects harmful cosmic rays and protects the planet from solar wind. The field reverses every couple of hundred thousand years. By using a model instead of a computer simulation, scientists hope to determine how these reversals occur and predict the next one.        Stats of Spin Little Earth: Both spheres are driven by 350-hp electric motors. At full speed the outer sphere spins at 240 rpm; the inner sphere reaches 960 rpm. Dangerous Metal: Sodium is highly conductive and melts more easily than iron, but it can explode if touched by water. (The lab in Maryland has no sprinklers.) Fuel Metal Jacket: The corrugated half-pipes around the sphere are filled with oil, not water or steam, that heats the sodium inside to its melting point, 207.9 F.  RELATED STORIES * PM NEWS: Large Hadron Collider to Turn on Sept. 10, Not End World  * PLUS: Hurricane Lab Will Simulate 155-mph Storm With &amp;quot;Wall of Wind&amp;quot;  * TECH WATCH: 5 Extreme Research Machines You Need to Know  * EARLIER: MIT Fights for Clean Power With Holy Grail of Fusion   "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.popularmechanics.com/science/a12075/4277476/>