Evolution of the Solar Nebula and Planet Growth Under the Influence of Photoevaporation

Abstract

The recent development of a new minimum mass solar nebula, under the assumption that the giant planets formed in the compact configuration of the Nice model, has shed new light on planet formation in the solar system. Desch previously found that a steady state protoplanetary disk with an outer boundary truncated by photoevaporation by an external massive star would have a steep surface density profile. In a completely novel way, we have adapted numerical methods for solving propagating phase change problems to astrophysical disks. We find that a one-dimensional time-dependent disk model that self-consistently tracks the location of the outer boundary produces shallower profiles than those predicted for a steady state disk. The resulting surface density profiles have a radial dependence of Sigma(r) \alpha r^(-1.25+0.88-0.33) with a power-law exponent that in some models becomes as large as ~Sigma(r) \alpha r^(-2.1). The evolutionary timescales of the model disks can be sped up or slowed down by altering the amount of far-ultraviolet flux or the viscosity parameter alpha. Slowing the evolutionary timescale by decreasing the incident far ultraviolet flux, or similarly by decreasing alpha, can help to grow planets more rapidly, but at the cost of decreased migration timescales. Although they similarly affect relevant timescales, changes in the far ultraviolet flux or alpha produce disks with drastically different outer radii. Despite their differences, these disks are all characterized by outward mass transport, mass loss at the outer edge, and a truncated outer boundary. The transport of mass from small to large radii can potentially prevent the rapid inward migration of Jupiter and Saturn, while at the same time supply enough mass to the outer regions of the disk for the formation of Uranus and Neptune.