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AST 309L
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Review for Test 2

AST. 309L - REVIEW FOR TEST #2
  1. Factors Important For n(e)
    1. Formation of the solar system
      1. Regularities in motion, condensation sequence in materials due to temp.
      2. Collapse of material to disk, accumulation of larger particles, gravitationally unstable collapse of planetesimals; collapse of gas onto cores in outer part of solar system to make giant planets
    2. Earth (and habitable planet) properties
      1. Formation of the earth, and "differentiating" of materials
      2. Atmosphere - produced by outgassing (more with more massive planet), not original accretion, much CO2 (but dissolved in oceans), left N2; all O2 produced by living organisms
      3. Liquid water probably essential - defines CHZ (CHZ smaller than HZ)
      4. CHZ size depends on: distance from star, albedo, rotation, greenhouse eff,...
      5. Range of CHZ uncertain due to Greenhouse effect
    3. Properties of a habitable solar system
      1. Luminous stars have large CHZ but short lifetime, so not good
      2. Main sequence star, < 1.25 Msun, Pop I (with heavy elements), for long enough life and enough heavy elements
      3. Very low mass stars also have problems, small CHZ, flares,tidal locking
      4. Binary stars mostly no good (2/3 of all stars)
  2. Life in the Solar System
    1. Venus
      1. Most like Earth, except for distance from sun; atm ~ 90X Earth, mostly CO2
      2. Runaway greenhouse effect - too hot for liquid water, gaseous water decomposed by UV, no way to get CO2 dissolved in liquid
      3. Significant volcanic activity, sulfuric acid clouds
    2. Mars
      1. Atmosphere about .006X Earth, mostly CO2, polar ice caps, pressure too low for liquid water, even though temp ok some places
      2. Old volcanoes (previous outgassing), no current ones, dry river beds
      3. Liquid water first 1 to 1.5 billion yrs probably?
      4. Evidence for more atmosphere in past from deuterium, etc.
      5. Viking life experiments; camera, GCMS (for organic compounds, i.e. dead things)
      6. Gas Exchange Experiment - look at gas products after "feeding" vitamins, amino acids; oxygen released by reactions with O-rich inorganic components
      7. Labelled Release Exp. - Miller-Urey nutrients; look for release of radioactive C; found but again probably reaction with peroxides, etc
      8. Pyrolytic Release Exp. - feed "activated" CO2 gas (like Mars atm), look for processing by life - unrepeatable results - exhaust gas contamination
    3. The Outer Solar System
      1. Jupiter - likely organic molecules - maybe "floaters and sinkers"; lightning, Giant Red Spot, suggestive of organic compounds in atmosphere
      2. Titan (moon of Saturn) - atmosphere of N and methane, denser than Earth's
      3. Tidal heating in moons (example, Io) provides source of energy
      4. Europa (moon of Jup.) - ice crust, maybe liquid water below from tidal heat
  3. Mars fossil evidence
    1. Background
      1. Antarctic meteorite, 4.5 bil yrs old, 16 mil yrs in space
      2. Composition -> from Mars
    2. Evidence
      1. Mineral deposits in crack - calcium carbonate (like limestone), plus iron sulfide and magnetite, rarely found together unless life
      2. Organic compounds, mostly PAH's also in crack - common byproduct of life
      3. Small rounded structures shaped like cells
    3. Controversy (counterarguments)
      1. Many processes can make observed minerals, may require high temperatures
      2. PAH's are common in interstellar space and chemical processes
      3. Cell-like shapes are MUCH smaller than typical Earth bacteria







 





4 October 2006
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