Cuesta College, San Luis Obispo, CA
[20 points.] Discuss how Pluto and how Earth's moon would each be classified by the International Astronomical Union if they were to exchange positions. (Consider them to be approximately the same mass.)
Solution and grading rubric:
- p = 20/20:
Correct. Pluto would become a moon of Earth's, while the Earth's moon would orbit the sun directly (and not be a moon), retain its round shape (and thus not be solar system debris), but as it would neither clear out nor dominate the Kuiper belt anymore than Pluto did, it would now be classified as a
dwarf planet, and not a planet. (May use dwarf planet synonymously with "planetoid" or "small planet.") - r = 16/20:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. One of the classifications is problematic, but the IAU classification scheme is systematically applied to both objects. - t = 12/20:
Contains right ideas, but discussion is unclear/incomplete or contains major errors. Some discussion of difference in lifetimes, but compounded/confounded with other factors. Problematic application 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. Uses criteria other than that defined by the IAU classification scheme. - v = 8/20:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. - x = 4/20:
Implementation/application of ideas, but credit given for effort rather than merit. - y = 2/20:
Irrelevant discussion/effectively blank. - z = 0/20:
Blank.
Section 70158
p: 20 students
r: 17 students
t: 10 students
v: 15 students
x: 3 students
y: 3 students
z: 1 student
A sample "p" response (from student 0805):
An illustrated "p" response (from student 1616):
A "p" response (from student 0013) anthropomorphizing Pluto and Earth's moon:
A sample "v" response (from student 3825) speculating on the mind-boggling implications of this Pluto-Earth's moon switch:
A sample "x" response (from student 5588) equating Pluto and Earth's moon:
A sample "y" response (from student 6948):
My response if I were taking this course is that the IAU classification scheme itself is unclear and and filled with errors. Stating that a dwarf planet is not a planet at all makes no linguistic sense. In astronomy, dwarf stars are still stars, and dwarf galaxies are still galaxies. The IAU scheme is also flawed in that it defines objects solely by where they are while ignoring what they are. So Earth's Moon, if it were in Pluto's orbit would not be considered a planet, but neither would Earth itself! No object fully "clears its orbit," so applied literally, the IAU definition would leave our solar system with zero planets.
ReplyDeletePluto in Earth's position would be a moon or secondary planet--a term that should be used to describe the round moons of all the planets.
One could say this question is unanswerable because the IAU classification was made by only four percent of its members in a procedure that violated its own bylaws. Therefore, one cannot draw any conclusions about how the entire IAU would vote if the other 96 percent were included; instead, conclusions are based on a decision by only a tiny percent who were in a particular room on a particular day.
That decision was immediately opposed in a petition of over 300 professional astronomers led by Dr. Alan Stern, Principal Investigator of New Horizons. The alternative they favor is keeping the term planet broad to encompass all non-self-luminous spheroidal objects in orbit around a star. We can then distinguish types of planets using subcategories such as terrestrial planets, gas giants, ice giants, dwarf planets, super Earths, hot Jupiters, etc.
Feel free to read more about efforts to reverse the IAU decision on my Pluto blog at http://laurele.livejournal.com