Cuesta College, San Luis Obispo, CA
An astronomy question on an online discussion board[*] was asked:
Pd: Pluto is orbited by Styx (smaller and irregular in shape). Why is Styx classified as a moon and not solar system debris? Or can it be both a moon and solar system debris?Discuss why this answer is incorrect, and how you know this. Explain using the International Astronomical Union classification scheme.
t153: It can be (and is) both.
Solution and grading rubric:
Correct. Of the three IAU requirements for a planet (orbits the sun directly, has a rounded shape, cleared/dominates its orbit) Styx does not meet the first question (orbits the sun directly), which immediately categorizes it as a moon. If Styx had met the first question (orbits the sun directly), its irregular shape would make it not satisfy the second question (has a rounded shape), and would then categorize it as solar system debris if it was not orbiting Pluto. Thus it is not possible in the IAU classification scheme to be both a moon and solar system debris.
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Discussion of either IAU classification scheme, or why online comment is incorrect is not clear.
Contains right ideas, but discussion is unclear/incomplete or contains major errors. Problematic discussion of both IAU classification scheme and why online comment is incorrect.
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.
Implementation/application of ideas, but credit given for effort rather than merit. Discussion unrelated to the IAU classification scheme.
Irrelevant discussion/effectively blank.
Exam code: finalst0P
p: 18 students
r: 4 students
t: 11 students
v: 0 students
x: 1 student
y: 0 students
z: 0 students
Exam code: finaln3rF
p: 13 students
r: 10 student
t: 5 students
v: 1 student
x: 0 students
y: 2 students
z: 0 students
A sample "p" response (from student 7433):
A sample "y" response (from student 9426):