20190502

Astronomy midterm question: possible IAU classification of "cubewano" 
2014 MU69?

Astronomy 210 Midterm 2, spring semester 2019
Cuesta College, San Luis Obispo, CA

A "cubewano" is defined as a Kuiper belt object whose orbit around the sun is not gravitationally controlled by Neptune or other planets[*]. Discuss whether or not a "cubewano" such as 2014 MU69 (nicknamed "Ultima Thule," shown at right[**]) could be considered a dwarf planet, and why. Explain using the International Astronomical Union classification scheme.

[*] wiki.pe/Cubewano.
[**] nasa.gov/sites/default/files/thumbnails/image/ultima-thule-1-ca06_022219.png.

Solution and grading rubric:
  • p:
    Correct. Discusses IAU classification scheme to argue that 2014 MU69 would meet qualification I (orbits the sun directly), but with its irregular shape would not meet qualification II (rounded shape), and thus be classified as solar system debris. (Note that as a Kuiper belt object, 2014 MU69 does not meet qualification III (dominates its orbit), but this does not affect its solar system debris classification. But may instead interpret 2014 MU69's shape is "round enough" in order to conclude that it would be classified as a dwarf planet.)
  • r:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
  • t:
    Contains right ideas, but discussion is unclear/incomplete or contains major errors. Explicitly lists IAU requirements, but does not apply them correctly/consistently.
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Discussion only tangentially related to the IAU classification scheme.
  • x:
    Implementation/application of ideas, but credit given for effort rather than merit. Discussion unrelated to the IAU classification scheme.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Section 30676
Exam code: midterm02SpsR
p: 27 students
r: 4 students
t: 5 students
v: 3 students
x: 2 students
y: 0 students
z: 0 students

A sample "p" response (from student 7563):

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