20171026

Astronomy quiz question: meeting the first two IAU planetary qualifications

Astronomy 210 Quiz 4, fall semester 2017
Cuesta College, San Luis Obispo, CA

Refer below to the minimal qualifications established by the International Astronomical Union for a planet:
I. Orbits the sun.
II. Shape "rounded-out" by gravity.
III. Cleared/dominates orbit around sun.
Which solar system object(s) meets both qualifications I and II, but does not meet qualification III?
(A) Earth.
(B) Megaclite, an irregular-shaped moon of Jupiter.
(C) Ganymede, a moon of Jupiter larger in size than Mercury.
(D) Eris, a dwarf planet.
(E) (More than one of the above choices.)
(F) (All of the above choices.)
(G) (None of the above choices.)

Correct answer (highlight to unhide): (D)

Earth orbits the sun (meeting qualification I); is "rounded out" in shape (meeting qualification II); and gravitationally dominates its orbit around the sun (meeting qualification III).

Megaclite orbits Jupiter (and does not directly orbit the sun, failing qualification I); is irregular in shape (failing qualification II); and does not dominate its orbit around the sun (failing qualification III), as it is gravitationally bound to orbiting Jupiter as Jupiter orbits the sun.

Ganymede orbits Jupiter (and does not directly orbit the sun, failing qualification I); is larger than Mercury in size and thus must be round in shape (meeting qualification II); and does not dominate its orbit around the sun (failing qualification III), as it is gravitationally bound to orbiting Jupiter as Jupiter orbits the sun.

Eris orbits the sun (meeting qualification I); is "rounded out" in shape (meeting qualification II); but does not gravitationally dominate its orbit around the sun, sharing it with other Kuiper Belt objects (fails qualification III).

Thus Eris is the only object listed here that meets qualifications I and II, but does not meet qualification III.

Section 70158
Exam code: quiz04nqyL
(A) : 1 student
(B) : 0 students
(C) : 2 students
(D) : 33 students
(E) : 6 students
(F) : 0 students
(G) : 0 students

Success level: 80% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.50

Section 70160
Exam code: quiz04N3rn
(A) : 1 student
(B) : 0 students
(C) : 1 student
(D) : 22 students
(E) : 3 student
(F) : 0 students
(G) : 2 students

Success level: 77% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.67

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