IGPP Seminar Series

Turbulence in the Outer Solar Nebula

by Dr. Neal Turner
JPL

Abstract

The Solar system formed from a disk of gas and dust around the young Sun. The disk evolved by the outward transfer of orbital angular momentum and the mixing of material between hot and cold regions. Major uncertainties center on the effects of turbulence in the evolution. I will discuss 3-D MHD calculations of patches of the outer nebula, showing the turbulence driven by the magnetorotational instability is stratified: both angular momentum transfer and mixing are slow near the equatorial plane and rapid in the surface layers, contrasting with the common assumption that the accretion stress is proportional to the pressure. The spreading of a trace species is well-matched by solutions of a damped wave equation, and the damped wave picture will be useful for chemical evolution models. However, even in calculations where mixing reaches a time-averaged steady state, the chemical concentration at any given point fluctuates substantially due to changes in the direction of the flow, so that as well as mixing species formed under widely varying conditions, the turbulence intermittently forces the nebula away from local equilibrium. This effect is missing from diffusion models. The gradient in transport rates between the surface layers and interior and the intermittency of the turbulence will affect estimates of the molecular abundances and models of the growth of solid particles during the formation of the planets.
Tuesday, 17 January 2006
3845 Slichter Hall
Refreshments at 3:45 PM
Lecture at 4:00 PM