Earth’s core (1:106 scale)

This unusual device is a laboratory model of Earth’s core. The experiment aims to study the self-generation of magnetic fields as occurs in the geodynamo. The temperature of Earth’s iron core precludes ferromagnetism; our planetary field instead comes from induction, analogous to processes converting mechanical motions to electric currents in an electric generator. Yet deep mysteries remain about the structure and dynamics of Earth’s magnetic field. The need to understand it is driving experimental efforts worldwide (see the article on page 40 ), including this 3-meter-diameter model dynamo at the University of Maryland.

Shown here is the outer spherical vessel, whose temperature-regulating jacket gives it a ribbed appearance. Inside is a 1-meter-diameter sphere that simulates Earth’s solid inner core. Both spheres rapidly rotate (see http://www.youtube.com/user/n3umh ), but the more hazardous aspect is the 12 tons of liquid sodium that will fill the intervening space to model the liquid iron of the outer core. In early studies conducted using water, the kinetic energy provided by the two rotating spheres induced a variety of complex states, including turbulent bi-stability—the switching between two distinct states over long time periods, suggestive of the polarity reversals of Earth’s magnetic field. (D.S.Zimmerman. D.S.Zimmerman, S.A.Triana. S.A.Triana, D.P.Lathrop. D.P.Lathrop, Physics of Fluids 23 6 065104 (2011). 10.1063/1.3593465 10706631; image courtesy of Dan Lathrop.)

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