Astronomy midterm question: IAU classification of centaurs

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

In our solar system, "centaurs" are objects that:
...circulate [around the sun] between Jupiter and Neptune on unstable orbits that cross the paths of one of the jovian planets. That means they're probably doomed, within ten million years or so, to be flung into the inner solar system or out into interstellar space... There's a lot that's not known about centaurs, including how many have enough gravity to pull themselves into a round shape, which would earn them the title of "dwarf planet."[*]
Discuss how centaurs that are not dwarf planets should be classified. Explain using the International Astronomical Union classification scheme.

[*] Marcus Woo, "First Asteroid With Rings Discovered" (March 26, 2014), on.natgeo.com/1h3G1oI.

Solution and grading rubric:
  • p:
    Correct. Of the three IAU requirements (orbits the sun directly, has a rounded shape, cleared/dominates its orbit), a dwarf planet satisfies the first two. A centaur that is not able to be a dwarf planet would then not be rounded in shape, but still share an orbit around the sun with the jovian planets, classifying 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 categorizing centaurs that aren't dwarf planets must be solar system debris, but discussion of requirements is not explicit, or only implied.
  • 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 30674
Exam code: midterm02n4s5
p: 10 students
r: 3 students
t: 7 students
v: 2 students
x: 0 students
y: 0 students
z: 0 students

Section 30676
Exam code: midterm02sLoX
p: 28 students
r: 6 students
t: 18 students
v: 1 student
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 1597) using the IAU classification flowchart:

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