Astronomy final exam question: Interpreting IAU classification of Pluto

Astronomy 210 Final Exam, Fall Semester 2010
Cuesta College, San Luis Obispo, CA

[20 points.] An astronomy question on an online discussion board (http://answers.yahoo.com/question/index?qid=20060816202219AA5qzCL) was asked and answered:

ne0aes0p: Why is Pluto not a planet anymore?

crown1114: Well, because based on [the IAU] definition of a planet, Pluto...satisfies only 1 criteria and according to them, 2 criteria must be satisfied in order to be called a planet.

Discuss whether this statement is correct or incorrect, and how you know this. Explain using the International Astronomical Union classification scheme.

Solution and grading rubric:

• p = 20/20:
  Correct. The online comment is incorrect, as Pluto needs to satisfy three requirements (orbits the sun, has a rounded shape, cleared/dominates its orbit) to be a planet, of which only the first two are actually satisfied.
  
• r = 16/20:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Discussion of IAU requirements, or why online comment is incorrect is not clear.
  
• t = 12/20:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. Problematic discussion of IAU requirements and why online comment is incorrect.
  
• v = 8/20:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Discussion of criteria only tangentially related to the IAU requirements.
  
• x = 4/20:
  Implementation/application of ideas, but credit given for effort rather than merit. Discussion of criteria unrelated to the IAU requirements.
  
• y = 2/20:
  Irrelevant discussion/effectively blank.
  
• z = 0/20:
  Blank.
  

Grading distribution:
Section 70160
p: 25 students
r: 5 students
t: 4 students
v: 1 student
x: 2 students
y: 0 students
z: 1 student

A sample "p" response (from student 7133), successfully applying a recreation of the IAU classification flowchart from memory:

Another sample "p" response (from student 9890), with a personal opinion regarding Pluto:

Another sample "p" response (from student 0802), with another personal opinion about Pluto, and kudos for the instructor: