20121214

Astronomy quiz question: IAU classification of Cruithne

Astronomy 210 Quiz 7, fall semester 2012
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.
Cruithne, an irregularly shaped body sharing Earth's orbit around the sun, is sometimes referred to as "Earth's second moon[*]." According to the IAU qualifications, Cruithne is classified as:
(A) a moon.
(B) solar system debris.
(C) a dwarf planet.
(D) a planet.
(E) (None of the above choices.)

[*] Lynn Carter, "Have Astronomers Discovered Earth's Second Moon?" curious.astro.cornell.edu/question.php?number=578.

Correct answer: (B)

Cruithne orbits the sun directly, so it is not a moon. However, due to its irregular shape, it is classified as solar system debris. (If Cruithne were rounded in shape, it would be classified as a dwarf planet, as it does not dominate its orbit around the sun.)

Section 70158
Exam code: quiz07sEcn
(A) : 7 students
(B) : 23 students
(C) : 3 students
(D) : 1 student

Success level: 70% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.56

Section 70160
Exam code: quiz07n0iC
(A) : 1 student
(B) : 24 students
(C) : 0 students
(D) : 0 students

Success level: 96% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.14

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