Cuesta College, San Luis Obispo, CA
[20 points.] Discuss why Pluto is now a dwarf planet under the International Astronomical Union classification scheme.
Solution and grading rubric:
- p = 20/20:
Correct. Discuss how Pluto orbits the Sun (and thus is not a moon), and has a rounded shape (and thus not an asteroid), but because it has neither cleared nor dominated its orbit, Pluto is not a planet, but a dwarf planet. - r = 16/20:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. At least recognizes how two out of the three IAU requirements applies (or does not apply) to Pluto. - t = 12/20:
Contains right ideas, but discussion is unclear/incomplete or contains major errors. Problematic discussion of IAU classification scheme. - 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.
Section 30676
p: 14 students
r: 10 students
t: 6 students
v: 14 students
x: 3 students
y: 1 student
z: 0 students
Another sample "p" response (from student 0301):
Another sample "p" response (from student 1988), with the IAU classification rules in list format:
Another sample "p" response (from student 4498), with the IAU classification rules in a flowchart format:
Yet another sample "p" response (from student 5065), illustrating how the third IAU classification rule is not met by Pluto:
A sample "t" response (from student 1192) where the IAU classification rules are listed, but are not correctly applied to Pluto:
A sample "v" response (from student 0022):
Another sample "v" response (from student 2517) that gets sentimental on behalf of Pluto:
Another sample "v" response (from student 2626), appealing to both Pluto being neither terrestrial nor jovian in nature, and also not being "King of the Kuiper belt":
A sample "x" response (from student 4200):
A sample "y" response (from student 8789):
It is the IAU classification scheme that should get a ZERO. Pluto is still a planet. Only four percent of the IAU voted on the controversial demotion, and most are not planetary scientists. Their decision was immediately opposed in a formal petition by hundreds of professional astronomers led by Dr. Alan Stern, Principal Investigator of NASA’s New Horizons mission to Pluto. One reason the IAU definition makes no sense is it says dwarf planets are not planets at all! That is like saying a grizzly bear is not a bear, and it is inconsistent with the use of the term “dwarf” in astronomy, where dwarf stars are still stars, and dwarf galaxies are still galaxies. Also, the IAU definition classifies objects solely by where they are while ignoring what they are. If Earth were in Pluto’s orbit, according to the IAU definition, it would not be a planet either. A definition that takes the same object and makes it a planet in one location and not a planet in another is essentially useless.
ReplyDeleteNo planet fully clears its orbit of asteroids, and Neptune does not clear its orbit of Pluto. Applied literally, this criteria could be taken to mean our solar system has no planets. The IAU likely meant that a planet should gravitationally dominate its orbit.
These reasons are why many astronomers, lay people, and educators are either ignoring the demotion entirely or working to get it overturned. Pluto is a planet because it is spherical, meaning it is large enough to be pulled into a round shape by its own gravity--a state known as hydrostatic equilibrium and characteristic of planets, not of shapeless asteroids held together by chemical bonds.
Why not make the most logical choice, which is to make dwarf planets a subclass of planets that are planets because they are in hydrostatic equilibrium but are of the dwarf category because they do not gravitationally dominate their orbits?
I am a writer and amateur astronomer and proud to be one of these people. You can read more about why Pluto is a planet and worldwide efforts to overturn the demotion on my Pluto Blog at http://laurele.livejournal.com