Astr1210 - Exam 3

Note that there were 101 points on this test total.  Posted scores
are to be thought of as out of 100 points 


          1 11111 11112 22222
12345 67890 12345 67890 12345
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DCBAE CCBBC DDABA DADBD DEBCB 

26.  Which regions of the Earth surface are the youngest?

    the ocean basins 

27.  Which terrestrial planet has the largest iron core (as a fraction of its total size)?

   Mercury

28.  Which terrestrial planet rotates slowly "backwards"?

   Venus

29.  Which of the two methods for planetary detection depends strongly on how the planetary system orbits 
        are tilted from our perspective, requiring almost exact alignment?
        

   Transits

30.  What is the name of the geological boundary associated with the disappearance of the dinosaurs (just
       two letters will do)?
                                                                                                                                  KT                                                                                               

31.  How long ago did the Solar System form?

  4.6 billion years ago

32.  Satellites of the Jovian planets are primarily made of what material?

  ice

SHORT Answer (6 points each).

33.  What is planetary migration?  What problem does it solve?


     During solar system formation the orbital distance of a planet from its
     star can change (typically decrease) due to coupling between the planet's
     gravity and that of the particles in the disk.  

     Migration is used to explain why we find Jovian-sized worlds closer 
     to their stars than Mercury is to the Sun when the expectation is that
     these worlds form out where Jupiter forms.

34. What evidence is there for ice on the planet Mercury?  Where is it located?


     The MESSENGER spacecraft has returned images of deep craters at the poles of
     Mercury that are cold at the bottom because the crater floor is always in
     shadow.   You also needed to mention that radar observation from Earth show
     high reflectivity regions (consistent with ice) at Mercury's poles - and those
     locations correspond exactly to the locations of deep shadowed craters.

35.  LIST the steps involved in the evolution of the composition of the Earth's atmosphere from its initial
       formation to the present day. 


       - Production of an initial CO2 dominated atmosphere through outgassing and impacts
          with Nitrogen as the 2nd most abundant gas
 
       - Formation of liquid water oceans which removed the CO2 and deposited it as rock
           leaving Nitrogen as the main constituent of the atmosphere.

       - Production (much later) of oxygen by plant photosynthesis leading to today's 
          Nitrogen + Oxygen atmosphere.


36.  Make a SKETCH to illustrate how the greenhouse effect works (labels only, no sentences).

       see http://www.astro.virginia.edu/class/skrutskie/images/greenho.gif

     Important in a complete answer

        -VISIBLE sunlight reaches the surface through a TRANSPARENT
          CO2 atmosphere and warms the surface  (note you had to identify 
          a greenhouse gas - ideally CO2)
  
        - The warmed surface glows with INFRARED light.  CO2 is
           OPAQUE to infrared light.  The energy is effectively 
           trapped.


37.  Define the following terms in a short sentence (or less):

Differentiation:  Gravitational separation of rock from iron in a molten planet (dense stuff sinks
                 to the center.


Keyhole:  A small region of space that, if an asteroid passes through it, it will be directed onto
               a collision course with the Earth, striking Earth on it's next pass.




Breccia:  A rock consisting of many different rock types (regolith) fused together by the heat of
           impact.




Half-life: The time it takes for 1/2 of the atoms in a sample of a radioactive isotope to decay.




Accretion:  Particle growth to larger size via sticking and gravitational accumulation in 
               a planet-forming disk.