Astronomy final exam question: making Pluto a planet (again)?

Astronomy 210 Final Exam, Fall Semester 2009
Cuesta College, San Luis Obispo, CA

[20 points.] Write down the three qualifications established by the International Astronomical Union for a planet. Discuss how one or more of these qualifications should be changed/eliminated such that Pluto would again be considered a planet.

(Photo credit: Untitled, Zara Evans, November 19, 2006, http://www.flickr.com/photos/zara/301724221/).

Solution and grading rubric:

• p = 20/20:
  Correct. Pluto already satisfies the first two IAU classification requirements (orbits the sun, and has spherical shape), but does not satisfy the third requirement, as Pluto does not clear/dominate its orbit. If this rule were eliminated, then Pluto would again become a planet.
  
• r = 16/20:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Instead of eliminating the third IAU requirement, argues that Pluto should instead satisfy it if were to somehow clear/domintate its orbit.
  
• t = 12/20:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. Problematic discussion, but at least understands IAU classification scheme.
  
• v = 8/20:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Only partial understanding of 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: 30 students
r: 5 students
t: 3 students
v: 2 students
x: 0 students
y: 1 student
z: 0 students

Section 70158
p: 40 students
r: 0 students
t: 0 students
v: 4 students
x: 1 student
y: 0 students
z: 2 students

A sample "p" response (from student 8260):

Another sample "p" response (from student 8624), with an appeal to the head of Abraham Lincoln:

A sample "r" response (from student 7094), where it would be easier to change Pluto's orbit than to change the IAU rules?

A sample "v" response (from student ):

Another sample "v" response (from student 2857):

A speculative "x" response (from student 2388):

Cf. a similar question (Cuesta College, Spring 2009) regarding Pluto's status in an earlier post:
Astronomy final exam question: Pluto not a planet?.