Astronomy midterm question: provisional IAU classification of 2014 UZ224?

Astronomy 210 Midterm 2, fall semester 2016
Cuesta College, San Luis Obispo, CA

Solar system object 2014 UZ224 was recently discussed in the news[*]:
Scientists have discovered a new object orbiting the sun in the Kuiper belt, called 2014 UZ224, which measures about 330 miles across. The smallest object in the solar system that has earned the title of "dwarf planet" (prior to this new discovery) is Ceres, which lies in the asteroid belt between Mars and Jupiter. Ceres is 590 miles across. The object 2014 UZ224 might not be a dwarf planet, but that will have to be decided by the International Astronomical Union.
Discuss why 2014 UZ224 may not qualify as a dwarf planet. Explain using the International Astronomical Union classification scheme.

[*] Calla Cofield, "New Dwarf Planet Found in Our Solar System" (October 12, 2016), scientificamerican.com/article/new-dwarf-planet-found-in-our-solar-system/.

Solution and grading rubric:
  • p:
    Of the three IAU requirements (orbits the sun directly, has a rounded shape, cleared/dominates its orbit), a dwarf planet satisfies the first two. Since UZ224 orbits the sun, in the Kuiper belt (satisfying the first and third requirement), in order to not be classified as a dwarf planet, UZ224 must not be so large that its shape has been rounded (which would classify it as solar system debris).
  • r:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Understands how IAU requirements apply in correctly arguing how UZ224 would not be classified as a dwarf planet, but discussion of requirements is not explicit, or only implied, or contains extraneous information.
  • 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:
Grading distribution:
Section 70158
Exam code: midterm02sU6A
p: 30 students
r: 3 students
t: 3 students
v: 5 students
x: 0 students
y: 0 students
z: 0 students

Section 70160
Exam code: midterm02NbnW
p: 23 students
r: 0 students
t: 1 student
v: 0 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 0022):

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