Astronomy quiz question: IAU classification of Ceres as a Kuiper belt object in the past

Astronomy 210 Quiz 4, spring semester 2018
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.
Observations from NASA's Dawn spacecraft indicate that the dwarf planet Ceres may have been located in an outer orbit around the sun in its past[*]:
New observations suggest that Ceres may have been knocked into the main asteroid belt from the solar system's chillier outskirts. Discovery of ammoniated clays on its surface indicates that Ceres was born somewhere beyond the orbit of Neptune, where the sun's weaker glare would not vaporize and scatter the ammonia as the minerals formed. Then, sometime in the following 500 million years, gravitational pulling from jovian planets may have thrown it inward, delivering it to the main asteroid belt between Mars and Jupiter.
According to the IAU qualifications, if Ceres in the past had an orbit in the Kuiper belt, it would have been classified as:
(A) a moon.
(B) solar system debris.
(C) a dwarf planet.
(D) a planet.
(E) (None of the above choices.)

[*] Michael Greshko and Nadia Drake, "Largest Object in Asteroid Belt May Have Come From Elsewhere," news.nationalgeographic.com/2015/11/151110-ceres-dawn-ammonia-outer-solar-system-nasa/.

Correct answer (highlight to unhide): (C)

As a dwarf planet today, Ceres directly orbits the sun (meeting qualification I), has a rounded shape (meeting qualification II), but does not satisfy qualification III (as it shares its orbit around the sun with the asteroids). If Ceres was in the Kuiper belt in the past, it would still have orbited the sun (meeting qualification I), had a rounded shape (meeting qualification II), but still did not satisfy qualification III (as it would have shared its orbit around the sun with the Kuiper belt objects).

Section 30674
Exam code: quiz04sLrW
(A) : 5 students
(B) : 6 students
(C) : 19 students
(D) : 7 students
(E) : 0 students

Success level: 52% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.34

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