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Incoming links: Planetary system
Philip J. Armitage Created 2026-10-20 Updated 2026-11-05
Philip J. Armitage develops the theory of planet formation and the early evolution of planetary systems. His lecture notes follow the sequence from the evolution of protoplanetary disks through planetesimal growth to terrestrial and gas giant formation.
An important physical connection is that formation and orbital evolution occur together. Planets exchange angular momentum with their surrounding gas, scatter smaller bodies and interact gravitationally with other planets. The resulting planetary migration means that an observed orbit need not identify the location where a planet originally acquired its mass.[ref]
Lecture notes on the formation and early evolution of planetary systems by Philip J. Armitage. Abstract and topical outline: disk evolution, planetesimal growth, migration, scattering and tides
Portrait of Philip J. Armitage
. External portrait hosted by JILA, University of Colorado Boulder. Source. Planetary system 2026-11-05
A planetary system consists of planets and associated smaller bodies orbiting a star or stellar multiple. Satellites, rings, debris and residual gas can contribute to its dynamics even when only the planets are easily observed.
The bodies interact gravitationally rather than following permanently independent ellipses. Orbital resonances, close encounters and tidal evolution can change their arrangement. Observations also sample different components: transit measurements constrain projected geometry and radius ratios, while stellar radial velocities constrain masses through the system's reflex motion. Combining such measurements provides a more complete description than counting detected planets alone.