Planet Formation

1
Planet Formation

• stars formed by gas/dust cloud contracting due
  to gravity
• gives swirling disk of material. Hot near center,
  cooler further away
• material can condensate if cool enough
  (gas-gtliquid/solid)
• density falls with distance. Planet formation
  occurs when not too far and not too close

2
Planet Formation II

• once condensation starts, protoplanets can grow
  in size
• -objects collide and stick together
• -gravity pulling together
• if big enough, and cool enough, can
  gravitationally hold on to light gases (H,He)
  JUPITER
• but if H,He dispersed by new star, never grabbed
  EARTH

3
Planet Formation III

• close to star have planets made from heavy
  elements (iron,nickel,silicon)
• -water probably came later from comets
  hitting surface after it had cooled
• further from star are Gas Giants as ices (water
  H2O, methane CH4) froze out early allowing more
  material to accrete
• mostly circular orbits as rest collided with
  larger protoplanets

4
Planets in other Star Systems

• test out how planets are formed with more
  examples
• first extrasolar planet observed in 1995. In Jan
  2000, 28 observed and now more than 40. At least
  one system with 2 observed planets
• perhaps in the future observe light (visible or
  IR)
• now mostly look for wobble of Star (Doppler
  shift) due to gravity of planets
• if multiple planets need to sort out
  complications - takes years

5
Planetary Atmospheres

• composition of a planets atmosphere depends on
• Surface Gravity
• Temperature
• light atoms/molecules move faster than heavy
  molecules
• if velocity escape velocity gas leaves planet
• Mercury, Moon all escape
• Earth lightest (H,He) escape
• Jupiter none escape

6
Familiar Molecules

• molecule mass
• H2 hydrogen 2
• He helium 4
• CH4 methane 16
• NH3 ammonia 17
• H20 water 18
• N2 nitrogen 28
• O2 oxygen 32
• CO carbon monoxide 28
• CO2 carbon dioxide 44