20170323

Astronomy quiz question: IAU classification of spherically-shaped(?) Chariklo

Astronomy 210 Quiz 4, spring 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.
Chariklo is an object that has an unstable orbit around the sun, directly influenced by Uranus' gravity. Chariklo is surrounded by two rings (nicknamed "Oiapoque" and "Chuí"), and probably has at least one small moon still waiting to be discovered. The exact shape of Chariklo is not yet completely known. According to the IAU qualifications, if Chariklo is found to have a rounded shape, it would be classified as:
(A) a moon.
(B) solar system debris.
(C) a dwarf planet.
(D) a planet.
(E) (None of the above choices.)

[*] eso.org/public/news/eso1410/.

Correct answer (highlight to unhide): (C)

Chariklo directly orbits the sun (meeting qualification I), and with a spherical shape, it would also satisfy qualification II. However, it does not satisfy qualification III (as it is directly influenced by Uranus' gravity), which would then classify Chariklo as a dwarf planet. (If Chariklo had an irregular shape, then it would only meet qualification I, while not meeting qualifications II and III, which would then classify it as solar system debris.)

Section 30674
Exam code: quiz04nqyL
(A) : 2 student
(B) : 2 students
(C) : 15 students
(D) : 2 students
(E) : 1 student

Success level: 66% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.83

Section 30676
Exam code: quiz04sl4M
(A) : 6 students
(B) : 2 student
(C) : 26 students
(D) : 5 students
(E) : 0 students

Success level: 70% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.39

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