ISP205 Lecture #14, Feburary 22, 2001

  1. Review: terrestrial Planets:
    1. Order of geological activity: (most active to least active)
      Earth, Venus, Mars, Mercury + Moon
    2. This can be explained with the different sizes
    3. Except Venus all terrestrial planets have older highlands
      and younger lowlands.
    4. Only Earth and Venus have active volcanoes.
      Mars might have rare, occasional volcanic eruptions.
    5. Only Venus, Earth, and Mars have atmospheres
      Venus: ~100 times thicker atmosphere than earth
                  made mainly of CO2 and N2
      Mars  : ~100 times thinner atmosphere than earth
                  same composition than Venus atmosphere
      Earth: made mainly of N2 and O2
                 (modified because of life on earth)
    6. The very different surface conditions on Venus, Earth, and
      Mars are a consequence of the different greenhouse effects.
    7. Only Mercury and Earth have a detectable magnetic field.
    8. Water is found on Mercury, Earth, Moon, Mars but not
      on Venus.
    9. Liquid water is only found on Earth.
    10. There are indications that Mars had liquid water in the past.
      1. There are flow channels, mostly dating back to 3 billion years
        (flowing water requires a thicker atmosphere to prevent rapid
        evaporation - or an ice layer)
      2. There are hints of more recent floods
  2. The Giant Planets - Overview
    (see picture of size comparison)
    (see pictures of the giant planets)
    Planet Size (1 = earth) Spin Orbit Axis tilt (degree)
    Jupiter 11 10 hours 12 years 3.1
    Saturn 9.4 10 hours 29 years 27
    Uranus 4.0 17 hours 84 years 98
    Neptun 3.9 16 hours 165 years 29
  1. Whats inside ? The Galileo Mission to Jupiter
    (Redshift demo of orbit)
    (Picture sequence of Mission)
    (Picture sequence of Mission results)
    Going beyond the probe:
    Distance from center Composition Temp. Pressure
    Probe destroyed   426 K (153oC) 22 bar
    59-71 Tkm H2,He gas/liquid    
        11,000 K 3 Mio bar
    14-59 Tkm metallic H    
        25,000 K 12 Mio bar
    7-14 Tkm "ice" (C,N,O + H)    
    0-7 Tkm "rock" (Si, O, ...)    
    center   40,000 K 50 Mio bar
  2. Internal Composition of the Giant Planets - comparison
    (picture from book)
    1. Jupiter
      1. Outer atmosphere: 86% H2, 14%He, traces of CH2, NH3
      2. Inner composition: metallic H, and small core of ice, and rock
    2. Saturn
      1. Very similar to Jupiter, but much less Helium:
        97%H, 3%He
      2. Explanation: He rained down towards center (fractionation)
    3. Uranus
      1. Outer atmosphere: 83% H2, 15% He, 2% CH4
      2. Inner composition: Largely Ice and Rock
    4. Neptun
      1. Similar to Uranus - but somewhat more CH4:  3%
              
  3. Formation of the Giant Planets
    1. Why are the Giant Planets so different from the terrestrial ones ?
    2. Temperatures in the outer solar system much lower throughout 
      the history of the solar system. Therefore:
      1. Gravity of a terrestrial planet size object is enough to bind
        H and He (because molecule velocities are lower)
      2. Less solar wind (inverse square law) doesnt blow gas away
      3. Hydrogen can be bound in molecules like CH4 and NH2 
        that are stable at low temperatures and can form ice.
    3. Therefore outer planets could accumulate all H,He gas that 
      was around.
    4. Initial composition of the solar system: 84% H and 16% He !!
      (see picture)
      therefore giant planets can be much bigger than terrestrial ones
                 
  4. Atmospheric activity
    1. All giant planets have high speed winds because of rapid rotation
      and no friction with a solid surface.
    2. Typical windspeeds are:
      Jupiter: 200 m/s
      Saturn: 300 m/s
      Uranus: 200 m/s
      Neptun: 600 m/s
          
    3. Spots are hurricanes reflecting tubulence, bands are winds
      in opposite directions for upward moving hotter gas and 
      downward moving cooler gas.
           
    4. Degree of Turbulence/ Band formation is very different:
      1. Jupiter has the most turbulent wheather with many "hurricanes"
        and pronounced bands.
            (see pictures, movie)
      2. Saturn shows sometimes hurricanes in summer (every 30 years)
        and some band structure
      3. Neptun had hurricanes in 1986 (Dark spot) but not in 1994 anymore
        shows some band structure
      4. Uranus shows no signs of turbulence or bands
             
    5. Turbulence/ Band formation requires:
        - rapid rotation
        - internal heat source that triggers convective motion perpendicular 
          to rotation
      1. Jupiter, Saturn have a strong internal heat sources
      2. Neptun has a small internal heat source
      3. Uranus has no internal heat source
      4. Possible heat sources are:
        1. Primordial heat leftover from formation (Jupiter)
        2. Ongoing contraction
        3. He fractionation (Saturn - see low He in atmosphere)
  5. Magnetic fields
    1. Magnetic field formation requires rotation and a liquid, conducting
      core
    2. All giant planets have strong magnetic fields, but only Jupiter and
      Saturn have a liquid, conducting core of metallic hydrogen.
    3. The origin of the magnetic fields of Uranus and Neptun is unknown