Astronomy quiz question: possible IAU classification of 2015 TG387

Astronomy 210 Quiz 4, spring semester 2019
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.

2015 TG₃₈₇ (nicknamed "The Goblin") is an extremely distant object that is in orbit around the sun, located out beyond the extent of the Kuiper belt (where Pluto is located)[*]:

2015 TG₃₈₇ was discovered at a distance about two and a half times further away from the sun than Pluto. The location of 2015 TG₃₈₇ is similar to other known extremely distant objects, suggesting that something is pushing them into similar types of orbits around the sun. The similarities of the orbits of 2015 TG₃₈₇ and other extremely distant objects suggest the presence of an unknown planet several times larger than Earth--sometimes called "Planet X" or "Planet 9"--also orbiting the sun well beyond Pluto.

According to the IAU qualifications, if 2015 TG₃₈₇ is found to have a spherical shape, it would then be classified as:
(A) a moon.
(B) solar system debris.
(C) a dwarf planet.
(D) a planet.
(E) (None of the above choices.)

[*] Press release, Carnegie Institute for Science, "New Extremely Distant Solar System Object Found During Hunt for Planet X" (October 02, 2018), carnegiescience.edu/news/new-extremely-distant-solar-system-object-found-during-hunt-planet-x.

Correct answer (highlight to unhide): (C)

Since 2015 TG₃₈₇ orbits the sun directly, it would pass qualification I; and if found to have a spherical shape it would pass qualification II; but as "Planet X" is "pushing" it and other objects into similar orbits around the sun, 2015 TG₃₈₇ would not be dominating its orbit around the sun, and would then be classified as a dwarf planet.

Section 30674
Exam code: quiz04n3Ni
(A) : 4 students
(B) : 1 student
(C) : 21 students
(D) : 4 students
(E) : 0 students

Success level: 73% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0

Section 30676
Exam code: quiz04Si3n
(A) : 3 students
(B) : 2 students
(C) : 22 students
(D) : 12 students
(E) : 0 students

Success level: 60% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.60