Astronomy midterm question: possible IAU classification of primordial black hole in Kuiper belt?

Astronomy 210 Midterm 2, fall semester 2019
Cuesta College, San Luis Obispo, CA

Consider the speculative statements below as factual:

Scientists think the gravitational pull of something in the outer solar system could be yanking Kuiper belt objects into strange orbits. This object is said to have a mass about 10 times that of Earth and an orbit around the sun 20 times farther out than Neptune's. A team of scientists led by Durham University claim it's a primordial black hole about the size and shape of a bowling ball.[*]

Based on the information given in this excerpt, discuss whether or not this "primordial black hole" could be considered a planet, and why. Explain using the International Astronomical Union classification scheme.

[*] Harry Pettit, "Mysterious Planet X May Be Black Hole That's '10 times Heavier than Earth but the Size of a Bowling ball' on Edge of Our Solar System" (September 30, 2019), thesun.co.uk/tech/10032900/planet-x-black-hole-solar-system/.

Solution and grading rubric:

• p:
  Correct. Discusses IAU classification scheme to argue that this primordial black hole would meet each of the qualifications:
  1. orbits the sun directly (20 times farther out than Neptune's orbit);
  2. has a spherical shape (like a bowling ball);
  3. dominates its orbit (gravitationally pulling Kuiper belt objects into strange orbits);
  such that it should be classified as a planet.
• r:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. May have overlooked or misinterpreted the gravitational influence of this primordial black hole on Kuiper belt objects.
• t:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. Explicitly lists IAU requirements, but does not apply them correctly/consistently.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Discussion based on garbled definitions of, or not based on proper or complete list of the IAU qualifications.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. Discussion unrelated to the IAU classification scheme.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.

Grading distribution:
Section 70158
Exam code: midterm02Rf0w
p: 25 students
r: 8 students
t: 1 student
v: 0 students
x: 0 students
y: 0 students
z: 0 students

Section 70160
Exam code: midterm02T4qz
p: 15 students
r: 5 students
t: 1 student
v: 1 student
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 5622):
Another sample "p" response (from student 7890):