4.2 Early solar system dynamics and planetary migrations

Planetary migration reshapes solar systems, explaining hot Jupiters and our own planets' positions. This process moves planets closer or farther from their stars, scattering smaller bodies and affecting terrestrial planet formation.

The Nice model shows how our gas giants' migration led to the Late Heavy Bombardment. This event heavily cratered the inner planets, potentially delivering water and volatiles crucial for Earth's habitability.

Early Solar System Dynamics

Concept of planetary migration

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• Planetary migration describes the process of planets changing their orbital distances from their host star over time
• Planets can migrate inward (closer to the star) or outward (farther from the star) relative to their initial orbits
• Planetary migration plays a crucial role in shaping the architecture of planetary systems
  • Explains observed orbital configurations that differ from initial positions (hot Jupiters)
  • Affects the distribution of smaller bodies (asteroids, comets) influencing impact frequency and intensity on planets
  • Inward migration of gas giants can disrupt terrestrial planet formation or cause ejections (WASP-47)
  • Outward migration of gas giants creates reservoirs of icy bodies (Kuiper Belt, Oort Cloud)

Nice model implications

• The Nice model proposes a scenario to explain the current orbital configurations of the solar system's outer planets
• Initially, Jupiter, Saturn, Uranus, and Neptune formed in a more compact configuration than their current orbits
• A disk of icy planetesimals existed beyond the orbits of the gas giants
• Gravitational interactions between the gas giants and planetesimals caused planetary migration
  1. Jupiter migrated slightly inward
  2. Saturn, Uranus, and Neptune migrated outward
• Migrating gas giants scattered planetesimals, ejecting some from the solar system and sending others into the inner solar system
• Scattered planetesimals likely caused the Late Heavy Bombardment, a period of intense cratering on terrestrial planets and the Moon
• The final post-migration orbital configurations of the gas giants match their current positions

Evidence and Impact of Planetary Migration

Evidence for planetary migration

• Hot Jupiters provide evidence for planetary migration
  • Gas giants orbiting very close to their host stars with orbital periods < 10 days (51 Pegasi b)
  • Likely formed farther out in the protoplanetary disk and migrated inward through disk interactions or planet-planet interactions
  • Prevalence of hot Jupiters suggests migration is common in planetary systems
• Late Heavy Bombardment (LHB) supports the occurrence of planetary migration
  • Period of intense cratering on terrestrial planets and the Moon ~4.1 to 3.8 billion years ago
  • High impact frequency during LHB suggests a sudden influx of impactors
  • Migrating outer planets in the Nice model could have caused the LHB
  • Cratering records on the Moon and terrestrial planets provide evidence for the LHB and indirectly for planetary migration

Impact on terrestrial planets

• Inward migration of gas giants can disrupt terrestrial planet formation
  • Perturbs orbits of forming terrestrial planets causing collisions or ejections (Kepler-10)
  • Results in fewer, more massive terrestrial planets or complete absence of terrestrial planets
• Outward migration of gas giants can deliver water and volatiles to terrestrial planets
  • Scatters icy planetesimals from outer regions into inner regions of the solar system
  • Impacting planetesimals deliver water and volatiles to terrestrial planets (Earth)
  • Delivery of these materials may be crucial for developing habitable conditions
• Migration of gas giants influences the final orbital configurations of terrestrial planets
  • Gravitational influence of migrating gas giants affects the settling of terrestrial planets into their current orbits
  • Resulting orbital configurations impact planets' climates, tidal heating, and long-term orbital stability (TRAPPIST-1)