ISP205 Lecture #15, Feburary 27, 2001

  1. Announcements
    1. New feature on the Web Site: Quiz Answers
    2. Bonuspoint Project #2 available on web site
      Due: March 18
    3. Special Bonuspoint Project #3 will be opened after spring 
      break: Write about an astronomy related experience
      during spring break.
      Rules:
      • One brief paragraph is sufficient
      • PG-13 max !
      • Good for 2 special Joker Bonuspoints
        (can be applied to anything)
      • There will be a vote for the best story
        2 best stories obtain another 4 points each
            
  2. Review Giant Planets
    1. Giant Planets have no surface as terrestrial planets, but
      have a huge atmosphere and a liquid and solid core.
    2. Very fast winds in the atmosphere, because of rapid
       rotation and no surface where friction could slow them.
    3. "Surface" features formed by winds:
      1. Zones and Belts are bands where convection moves
        gas upward or downward respectively
      2. Winds in zones and belts go in opposite directions
      3. Spots are "Hurricanes" forming around high pressure
        regions (Turbulence) at interface of opposite wind
        streams.
        (see picture)
    4. Giant Planets formed in colder region of solar system:
      Ices (CH2, H2O, ...) and light gases (H, He) can be used to built a planet and are the main constituents
    5. Giant Planets spin fast (10-17 hours) but orbit slow
    6. Jupiter:
      1. Very active atmosphere: permanent spots ("great red spot")
        pronounced zones and belts, lots of turbulence.
      2. Strong internal heat source, probably primordial heat
        from formation.
      3. Very strong magnetic field (100 x earth)
      4. Composition: H, He atmosphere, liquid metallic H ocean,
        some ices, "small" rocky core
      5. 3 cloud layers, top layer are Ammonia clouds (most visible)
      6. Hear Jupiter
    7. Saturn:
      1. Atmosphere shows zones and belts, but spots only
        temporarily during summer
      2. Internal heat source, probably He raining from atmosphere
        into core (Atmosphere is He depleted!)
      3. Strong magnetic field (comparable to earth)
      4. Composition and cloud layers similar to Jupiter
    8. Uranus:
      1. No atmospheric activity visible
      2. No internal heat source
      3. Strong magnetic field (comparable to earth)
      4. Composition: H,He,CH2 atmosphere, large amounts of
        ice and "small" rocky core.
      5. Ammonia cloud layer missing - condensed into snow
        Therefore darker, blueish surface compared to Jupiter/Saturn
      6. Uranus spins on its side - strongest seasons in the solar
        system.
    9. Neptune:
      1. Showed some atmospheric turbulence in 1986 (Voyager)
        (spots, scooter), but not today
      2. Internal heat source (contraction ?)
      3. Very strong magnetic field
      4. Composition similar to Uranus
      5. Record wind speeds in solar system: 1350 mph
        (supersonic winds)
  3. Pluto:
    1. Discovery of Neptune
      1. Predicted to exist by mathematicians John Adams,
        and Urbain Leverrier 1854,1846.
        (they determined size and position from deviations of
        Uranus orbit from Keplers Laws)
      2. Found by Johan Galle in 1846
    2. Discovery of Pluto
      1. Parcival Lowell calculated Plutos size and position
        from remaining, unexplained deviations in Uranus
        orbit - but deviations were not real !
      2. 1929 (13 years after Lowells death) search resumed
        at Lowells observatory.
      3. 1930 Clyde Tombaugh discovered Pluto after comparing
        hundreds of photographs (each with 160,000 stars).
        (picture of discovery)
           
    3. Plutos/Charons properties:
      1. Pluto: 2200 km diameter (half of Mercury)
      2. Orbits in 249 years and spins in 6.4 days, but
        spins "on its side" similar to Uranus
      3. Pluto has a moon: Charon
        1200 km diameter (biggest moon in solar system compared
        to its planet)
      4. Charon was discovered 1978 by James Christy from
        distortions in Plutos position (but not resolved)
        In 1987 Pluto and Charon were in occultation (Demo)
        and orbit/sizes could be measured (happens only every
        124 years !)
        (see HST movie)
      5. Charon and Pluto are tidally locked (orbit AND spin)
        seen from  Pluto the Moon doesn't move or spin at all
        (angular size of Charon: 3.5 degrees )
        what about moon phases ?
    4. Density: 2.1 g/cm2 - probably mixture of rock and water ice
    5. Surface temperature 50K (farthest from sun) to 60K (summer)
      Pluto also spins on its side - so summer lasts 124 years !
    6. Frozen surface, mainly water ice
    7. During summer a thin atmosphere of evaporated N2 (97%)
      and some CH2
    8. Origin: maybe a previous member of the Kuiper belt that
      accumulated material in collisions. Later collision formed
      Charon and explains tilted orbit and spin.
      This would mean that Pluto is not really a planet !
          
  4. Moons of the Giant planets
    1. Moon count:
        Book end of 2000
      Jupiter 16 28
      Saturn 19 22
      Uranus 18 21
      Neptune 8  

      Most new discovered moons are about 1-10 km large
          

    2. There are regular and irregular moons:
      regular moons: counter clockwise orbit (seen from north), 
              not very eccentric, in equatorial plane 
      irregular moons: "retrograde" clockwise orbit, highly eccentric,
              inclination out of equatorial plane
    3. Example: Jupiter has 8 regular moons, and 20 irregulars
      Redshift Demo
    4. 23 moons are larger than 200 km:
      (see picture)
      (discuss  6 largest)
    5. Triton (Neptune moon) (picture)
      1. Size: 80% of earth's moon
      2. Composition (and distance from sun) very similar
        to Pluto - related ?
      3. Lowest surface temperatures measured in the solar system:
        35-40 K, because high reflectivity (ice surface)
      4. Few impact craters - lots of geological activity ?
        Cyro-vulcanism: "Lava" of Ammonia/Water mixture,
        lakes and vapor geysers of Nitrogen
        (DEMO)
    6. Callisto (Jupiter moon) (picture)
      1. Size: exactly Mercury size
      2. Deep frozen, 
        not fully fractionated mixture of water ice and rock
      3. Surface older than 4 billion years - no geological
        activity
      4. Lots of craters, but fuzzy edges as ice evaporates
        somewhat
      5. Recent indication of liquid salt water ocean under
        thick ice layer (see Europa) 
    7. Ganymede (Jupiter moon) (picture)
      1. Size: slightly larger than Mercury
      2. Fractionated: Water ice crust, rock core
      3. Has magnetic field
      4. Some regions only ~1 billion years old
        geologically active ! (plate tectonics ?)
      5. New findings about liquid water, probably 
        sandwiched between ice layers (see Europa)
      6. What heats Ganymede ?
        Tidal forces from Jupiter (DEMO)
    8. Europa (Jupiter moon) (picture)
      1. Size: 65% Mercury (slightly bigger than earths moon)
      2. Mainly rocky interior with ice surface, hot metallic core
      3. Strong indications of liquid water ocean extending down 
        to rocky interior underneath thin ice crust 
        1. Recently formed surface features consistent
          with thin ice crust and underlying liquid ocean
        2. Presence of salt detected
        3. Magnetic field changes consistent with currents in liquid
          salt water induced by Jupiters magnetic fields.
      4. Deep sea volcanic activity likely - life ?
           
    9. Io (Jupiter moon) (movie and picture)
      1. Size: 75% Mercury
      2. Highest level of volcanism in solar system
      3. Lava is hot silicate lava as on earth (>1000 oC)
      4. Large parts of the surface replaced within decades
        (huge changes since Voyager flybys)
      5. Large deposits of sulfur snow - if snow melted by
        eruption: huge gas plumes visible from space
      6. Sulfurdioxide atmosphere
            
    10. Titan (Saturn) (picture)
      1. Size: Slightly larger than Mercury
      2. A moon with a fuzzy, orange atmosphere that blocks
        the view on the surface.
      3. Atmospheric pressure at surface: 1.6 bar (similar to earth)
      4. Atmospheric composition: mainly Nitrogen (similar to earth)
        plus lots of compounds: CO, Hydrocarbons, Hydrogen
        cyanide ...
        Complex molecules form at high altitudes under impact
        of UV light and block view
      5. Surface temperature: constant 90 K
        (picture of surface layers)
      6. Surface images in infrared show inhomogeneous surface
        (picture)
      7. Ethane and Methane could form lakes, rivers, on the
        surface (maybe an ethane wheather cycle, including
        ethane rain).
      8. Visibility at surface might be good, surface illumination
        in a dark orange.
      9. The Cassini space craft is on the way to Saturn and
        will drop a probe (Huygens) to land on Titan.
        (see picture)
  5. Rings of the Giant planets (pictures of rings pg 226/227 other
    book)
    1. All Giant Planets have rings; only Saturns are easily visible
    2. Rings are numerous pieces of ice, ranging in size from
      dust grains to meter sized boulders
    3. Mostly water ice (white) but organic compounds on
      surface can lead to dark rings
    4. Each particle orbits the planet like a little moon in a well
      confined plane (only 10-100 m thick)
    5. Rings are kept in place and structured by "shepards"
      1. Shepard moons within the ring systems sweep gaps
        into the rings
      2. Gravity from all moons confine little pieces to their
        orbits (and sweep them out of certain unstable orbits)
        keeping the rings in shape over time.
    6. Rings are probably very young (~50 Million years old)
    7. Rings form if a massive objects forms/enters the zone
      within the tidal stability limit of a massive planet.
      The object is disrupted and the pieces form a ring
    8. Triton is on the way and might be disrupted in ~100 Mio years
    9. Jupiters rings: mainly smooth dust (dark), probably from inner moons
    10. Saturns rings: Main rings A,B,C with Cassini Gap (4600 km)
      between A and B. Plus thin outer F ring.
      The A,B,C rings are very broad, very thin (~20 m)
              quite bright and easily visible from earth
      Closeup: really >1000 individual rings  (picture)
    11. Uranus rings (9 main): narrow, many meter sized boulders, hardly dust
      and very dark (among darkest objects in solar system)
    12. Neptune rings (4): very inhomogeneous (look like thin arcs)
      (picture)