Astronomy 101

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Homework Assignment SIX

  1. Graph the distribution of semi-major axes of  the known extrasolar planets.  This would be a plot similar to  Mass Distribution but with the ordinate being semi-major axis rather than mass. You will have to select appropriate bin sizes (e.g., 0.0-0.04 AU, 0.041-0.08 AU, etc.). What conclusions can you draw from this plot? [Note: if any of you can make a nice plot and save it as a gif file and email it to me, I'll add it to the lecture notes for this topic.]
  2. Given the large number of planets in very small orbits, and assuming the "spiraling in" modification of our planet formation theory is correct, do you think it likely that most giant planets spiral in and stop inside of 1 AU or spiral in and crash into their parent stars?
  3. Assume an as yet undetected planet orbits a nearby star that is identical to the Sun. The planet orbits at 0.06 AU (1/16th of the Earth's distance) such that it's orbital velocity is 1/16 that of Earth's, i.e. 1,860 m/sec.  Assume the smallest stellar velocity that you can detect (a real signal above the noise) is 12 m/sec.  What is the smallest mass planet you can detect?
  4. Why should solids form into planets (or protoplanetary cores) before gases, according to the most widely accepted model for planet formation?
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