Showing papers by "Andrew F. Cheng published in 1978"
TL;DR: The outer portion of the rings of Saturn is probably immersed in intense particle radiation belts and sputtering by high energy protons from the ice particles in the outer portion leads to a net erosion rate there of 10−6 cm yr−1 after allowance for the rapid recapture, and thus the redistribution, of water molecules on the ring particles as discussed by the authors.
Abstract: The outer portion of the rings of Saturn is probably immersed in intense particle radiation belts. We scale Pioneer 10 and 11 measurements to the Saturnian radiation belts and estimate that sputtering by high-energy protons from the ice particles in the outer portion of the rings leads to a net erosion rate there of 10−6 cm yr−1 after allowance for the rapid recapture, and thus the redistribution, of water molecules on the ring particles. The lifetime of ice particles in the outer portions of the rings against sputtering may then be less than the age of the solar system. We show that such water ice sputtering can maintain the neutral H atmosphere around the rings detected by Weiser et al. (1977). We also suggest that the very low albedo recently reported for the rings of Uranus could result from the sputtering away of primordial ices on the ring grains by Uranian radiation belt particles.
65 citations
TL;DR: In this article, simple exact solutions of the magnetohydrodynamic equations are found for rotating, magnetic stars, where the velocity and magnetic field are axisymmetric and purely toroidal, and the magnetic energy density equals the kinetic energy density.
Abstract: Simple exact solutions of the magnetohydrodynamic equations are found for rotating, magnetic stars. The velocity and magnetic field are axisymmetric and purely toroidal, and the magnetic energy density equals the kinetic energy density. For constant mass density, the solution reduces to that of Chandrasekhar (1956), which is stable even against non-axisymmetric perturbations. For an ideal gas equation of state, the condition for radiative thermal equilibrium is solved to lowest order in the non-spherical perturbation. The velocity, magnetic field and non-spherical pressure and temperature perturbations all vanish within cones centered around the rotation axis, |cos θ|>xi a zero of a Legendre polynomial. Low-order, long-period stellar oscillations may be excited by MHD instabilities near the equatorial region which become damped near the axis.
1 citations