Astronomy final exam question: Ceres as dwarf planet

Astronomy 210 Final Exam, fall semester 2008
Cuesta College, San Luis Obispo, CA

Discuss why Ceres, which orbits in the asteroid belt, is now a dwarf planet under the International Astronomical Union classification scheme.

Solution and grading rubric:

• p :
  Correct. Discuss how Ceres directly orbits the sun (and thus not a moon), and has a rounded shape (and thus not an asteroid), but because it neither has cleared nor dominates its orbit, it is not a planet, but 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. Problematic discussion of IAU classification scheme.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner.
  
• x:
  Implementation/application of ideas, but credit given for effort rather than merit.
  
• y:
  Irrelevant discussion/effectively blank.
  
• z:
  Blank.
  

Grading distribution:
Section 70160
p: 13 students
r: 8 students
t: 6 students
v: 0 students
x: 0 students
y: 3 students
z: 0 students

A sample "p" response, listing the IAU planetary criteria (from student 8187):

Another sample "p" response detailing how the IUA planetary criteria apply to Ceres (from student 4731):

A concise "p" response (from student 3111):

A whimsical "p" response (from student 8945), referring to a "Certificate of Achievement" awarded to each student on the last day of instruction:

A passionate "p" response (from student 0911), relating to fellow dwarf planet Pluto on a personal basis:

A sample "t" response (from student 1186), at least conveying the main idea with an illustration, despite questionable legibility: