Astronomy clicker question: why shouldn't Pluto be demoted?

Astronomy 10, Spring Semester 2007
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal M2.5

Students were asked the following clicker question (Classroom Performance System, einstruction.com) at the middle of their learning cycle:

[0.3 points.] Why should Pluto not be demoted from a planet to dwarf planet?
(A) Planet status, once given, cannot be revoked.
(B) It is the "king of the Kuiper belt."
(C) It has satellites (moons) of its own.
(D) (Pluto should be demoted from planet to dwarf planet.)

Correct answer: (none, opinion only, but see comments below).

Student responses
Section 4136
(A) : 9 students
(B) : 2 students
(C) : 9 students
(D) : 10 students

Section 5076
(A) : 3 students
(B) : 1 student
(C) : 9 students
(D) : 7 students

Each of these choices brings up opinions that many people have about demoting Pluto from planet to dwarf planet status. After the results of this clicker question are displayed, each of these issues are discussed.

(A) = "No takebacks." However, the first few asteroids that were discovered were touted as new planets, and astrological symbols were generated for them. But as more information was known about these "planets," there was determined to be many more of them in what is known as the asteroid belt, and their small size ultimately meant that their planetary status was stripped.


(B), (C) = "Pluto is special." Eris (2003 UB₃₁₃, or "Xena") is even bigger than Pluto, and also has a satellite. So it has even more of what made Pluto so "special."

(D) = So why should Pluto be a planet, once these objections are addressed?


Periodically updated comparison chart of the sizes of the Earth, Moon, Mercury, Ceres, Vesta, Pallas, Pluto, Xena, and other TNOs ("Trans-Neptunian Objects," aka Kuiper belt objects), posted by Wm. Robert Johnson (www.johnstonsarchive.net).