CAPTURE/TIDAL THEORY OF ZARA

• Jeans’ tidal theory

  James Jeans (1917) proposed a dualistic theory that separated formation of Sun from formation of planets.
• What does Jeans' Theory involve regarding the interaction between the Sun and a massive star?

  It involves three stages of interaction.
• What happens when a massive star passes within the Roche Limit of the Sun?

  It pulls out material in the form of a filament.
• What occurs to the filament after it is formed?

  It becomes gravitationally unstable and breaks into blobs that collapse to form proto-planets.
• What is the outcome of the proto-planet formation process described by Jeans' tidal theory?

  Planets are left in orbit about the Sun.
• What are the steps in Jeans' tidal theory of proto-planet formation?

  1. Filament forms from material pulled by the Sun.
  2. Filament breaks into proto-planets due to gravitational instability.
  3. Planets are left in orbit around the Sun.
• What does Jeans' tidal theory suggest about the stability of the filament?

  Jeans showed that the filament would be unstable and break into proto-planets.
• What are the difficulties associated with Jeans' tidal theory?

  • Very massive stars are rare and distant.
  • Low probability of a massive star coming close to another star.
  • Similar rotational period of Sun and Jupiter is expected if Jupiter's material was from the Sun.
  • In 1935, Henry Russell argued that material from the Sun cannot explain Mercury and other planets.
  • Spitzer noted a minimum mass for collapse of ~100 times that of Jupiter.
• Who proposed the modified version of Jeans' theory known as capture theory?M. Woolfson proposed capture theory in 1964.
• What does capture theory suggest about the Sun's interaction with nearby protostars?

  It suggests that the Sun drags a filament from a nearby protostar.
• How does capture theory explain the low rotation speed of the Sun?

  It explains that the Sun formed before the planets, leading to its low rotation speed.
• What does capture theory propose about the formation of terrestrial planets?


  It proposes that terrestrial planets formed due to collisions between protoplanets close to the Sun and giant planets.
• According to capture theory, how do planetary satellites form?


  They form due to condensation in drawn-out filaments.
• What are the difficulties associated with capture theory?

  • Space between local stars is too large for 9 planets and 60 moons to be caught by the Sun.
  • Millions would have to pass for one to be caught.
  • Planets would tend to spiral into the Sun, not encircle it.
  • Moons would not begin orbiting around planets; they would crash into the Sun or planets.
  • Cannot explain why the Sun and planets have the same apparent age (4.5 Gyrs).
• What happens to material at points B and B' in Jeans' tidal theory?

  Gravitational attraction causes material at B and B' to move towards A.

  
• What occurs to material at points C and C' in the context of Jeans' tidal theory?

  Material at C and C' experiences an outward force, producing high-density regions at D and D'.