20171026

Astronomy quiz question: IAU classification of irregularly-shaped(?) "Tyche"

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.
University of Louisiana at Lafayette astronomers propose[*] that "Tyche" may be a yet-undiscovered object orbiting the sun in the distant Oort cloud (a diffuse region of comets out beyond the Kuiper belt):
These researchers suggest that our sun may have a companion in the Oort cloud, which they have dubbed "Tyche," jostling the orbits of many comets there and causing some to fall toward Earth.
According to the IAU qualifications, if Tyche is found to have an irregular 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.)

[*] Charles Q. Choi, "Giant Stealth Planet May Explain Rain of Comets from Solar System's Edge," space.com/9612-giant-stealth-planet-explain-rain-comets-solar-system-edge.html.

Correct answer (highlight to unhide): (B)

Tyche directly orbits the sun (meeting qualification I), but with an irregular shape, it would not satisfy qualification II, classifying it as solar system debris. It may or may not satisfy qualification III (as it is not certain whether Tyche is merely "clearing," or has "cleared out" its orbit around the sun), but this does not affect its solar system debris classification.

Section 70158
Exam code: quiz04S4pR
(A) : 0 students
(B) : 42 students
(C) : 0 students
(D) : 0 students
(E) : 0 students

Success level: 100% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0

Section 70160
Exam code: quiz04N3rn
(A) : 2 students
(B) : 22 students
(C) : 2 students
(D) : 0 students
(E) : 0 students

Success level: 88% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.21

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