THE VISCOSITY OF LIQUID-IRON AT THE PHYSICAL CONDITIONS OF THE EARTHSCORE

It is thought that the Earth's outer core consists mainly of liquid ir on and that the convection of this metallic liquid gives rise to the E arth's magnetic field. A full understanding of this convection is hamp ered, however, by uncertainty regarding the viscosity of the outer cor e. Viscosity estimates from various sources span no less than 12 order s of magnitude(1,2), and it seems unlikely that this uncertainty will be substantially reduced by experimental measurements in the near futu re. Here we present dynamical first-principles simulations of liquid i ron which indicate that the viscosity of iron at core temperatures and pressures is at the low end of the range of previous estimates - roug hly 10 times that of typical liquid metals at ambient pressure. This e stimate supports the promotion commonly made in magnetohydrodynamic mo dels that the outer core is an inviscid fluid(3-5) undergoing small-sc ale circulation and turbulent convection(6), rather than large-scale g lobal circulation.