# Giant Planet Migration in Viscous Power-Law Discs

## TL;DR

This study systematically examines giant planet migration in viscous power-law discs, revealing that migration rate depends on disc surface density and is governed by angular momentum balance rather than viscous drift speed.

## Contribution

It provides a new understanding of migration dynamics in power-law discs, challenging previous assumptions about viscous drift speed influence.

## Key findings

- Migration rate is proportional to disc surface density.
- Migration governed by angular momentum balance, not viscous drift.
- Results are robust across different simulation parameters.

## Abstract

Many extra-solar planets discovered over the past decade are gas giants in tight orbits around their host stars. Due to the difficulties of forming these `hot Jupiters' in situ, they are generally assumed to have migrated to their present orbits through interactions with their nascent discs. In this paper, we present a systematic study of giant planet migration in power law discs. We find that the planetary migration rate is proportional to the disc surface density. This is inconsistent with the assumption that the migration rate is simply the viscous drift speed of the disc. However, this result can be obtained by balancing the angular momentum of the planet with the viscous torque in the disc. We have verified that this result is not affected by adjusting the resolution of the grid, the smoothing length used, or the time at which the planet is released to migrate.