Astronomy final exam question: IAU classification of Pluto and asteroids

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

[20 points.] According to the "Friends of Pluto," Pluto has been downgraded to an asteroid. Explain why Pluto and asteroids are each placed in different categories under the International Astronomical Union classification scheme.

(Photo credit: harlanm, "Eyewitless News: Save Pluto" contest, http://www.worth1000.com/emailthis.asp?entry=312604).

Solution and grading rubric:

• p = 20/20:
  Correct. Asteroids satisfy only the first IAU planetary requirement --that they orbit the sun--and because of their irregular shape, and their shared, non-dominating orbits, are classified as solar system debris. Pluto satisifes the first IAU requirement as well as the second (being rounded in shape), but because it does not dominate its orbit, is classified as a dwarf planet.
  
• r = 16/20:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
  
• t = 12/20:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. Problematic discussion, but at least understands IAU classification scheme. May discuss how asteroids and Pluto are different from the planet category, and/or placing them in the same non-planet category.
  
• 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 30674
p: 18 students
r: 1 student
t: 13 students
v: 7 students
x: 0 students
y: 1 student
z: 0 students

Section 30676
p: 23 students
r: 3 students
t: 15 students
v: 9 students
x: 14 students
y: 4 students
z: 0 students

A sample "p" response (from student 7272):


Another sample "p" response (from student 2569):


A terse sample "p" response (from student 1415):


A sample "p" response (from student 7615), insulting the intelligence of asteroids:


A sample "p" response (from student 1105), with a sad Pluto:


A sample "v" response (from student 1825), placing Pluto in the asteroid belt:


A sample "x" response (from student 4000):


A sample "y" response (from student 8282), with a commonly-held sentiment: