Theory of planet formation

Abstract

We review the current theoretical understanding how growth from micro-meter sized dust to massive giant planets occurs in disks around young stars. After introducing a number of observational constraints from the solar system, from observed protoplanetary disks, and from the extrasolar planets, we simplify the problem by dividing it into a number of discrete stages which are assumed to occur in a sequential way. In the first stage - the growth from dust to kilometer sized planetesimals - the aerodynamics of the bodies are of central importance. We discuss both a purely coagulative growth mode, as well as a gravoturbulent mode involving a gravitational instability of the dust. In the next stage, planetesimals grow to protoplanets of roughly 1000 km in size. Gravity is now the dominant force. The mass accretion can be strongly non-linear, leading to the detachment of a few big bodies from the remaining planetesimals. In the outer planetary system (outside a few AU), some of these bodies can become so massive that they eventually accrete a large gaseous envelope. This is the stage of giant planet formation, as understood within the core accretion-gas capture paradigm. We also discuss the direct gravitational collapse model where giant planets are thought to form directly via a gravitational fragmentation of the gas disk. In the inner system, protoplanets collide in the last stage - probably after the dispersal of the gaseous disk - in giant impacts until the separations between the remaining terrestrial planets become large enough to allow long term stability. We finish the review with some selected questions.

23 pages, 8 figures, proceedings workshop "Circumstellar disks and planets: Science cases for the second generation VLTI instrumentation", to appear in Astronomy and Astrophysics Review, ed. Sebastian Wolf

References in corpus (7)

• Rapid planetesimal formation in turbulent circumstellar discs
• Towards a Deterministic Model of Planetary Formation I: a Desert in the Mass and Semi Major Axis Distributions of Extra Solar Planets
• Coagulation, fragmentation and radial motion of solid particles in protoplanetary disks
• Models of Giant Planet formation with migration and disc evolution
• The formation and retention of gas giant planets around stars with a range of metallicities
• The evolution of gravitationally unstable protoplanetary disks: fragmentation and possible giant planet formation
• Trapping Solids at the Inner Edge of the Dead Zone: 3-D Global MHD Simulations

Cited by in corpus (7)

• ALMA Observations of Circumstellar Disks in the Upper Scorpius OB Association
• Extrasolar planets and brown dwarfs around AF-type stars. IX. The HARPS southern sample
• No significant correlation between radial velocity planet presence and debris disc properties
• VLT/SPHERE astrometric confirmation and orbital analysis of the brown dwarf companion HR 2562 B
• AB Aurigae: Possible evidence of planet formation through the gravitational instability
• VLA observations of the disk around the young brown dwarf 2MASS J044427+2512
• Adapting a solid accretion scenario for migrating planets in FARGO3D