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):

Astronomy midterm question: possible IAU classification of "cubewano" 2014 MU69?

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

A "cubewano" is defined as a Kuiper belt object whose orbit around the sun is not gravitationally controlled by Neptune or other planets[*]. Discuss whether or not a "cubewano" such as 2014 MU₆₉ (nicknamed "Ultima Thule," shown at right[**]) could be considered a dwarf planet, and why. Explain using the International Astronomical Union classification scheme.

[*] wiki.pe/Cubewano.
[**] nasa.gov/sites/default/files/thumbnails/image/ultima-thule-1-ca06_022219.png.

Solution and grading rubric:

• p:
  Correct. Discusses IAU classification scheme to argue that 2014 MU₆₉ would meet qualification I (orbits the sun directly), but with its irregular shape would not meet qualification II (rounded shape), and thus be classified as solar system debris. (Note that as a Kuiper belt object, 2014 MU₆₉ does not meet qualification III (dominates its orbit), but this does not affect its solar system debris classification. But may instead interpret 2014 MU₆₉'s shape is "round enough" in order to conclude that it would be classified as a dwarf planet.)
• r:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
• 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 only tangentially related to the IAU classification scheme.
• 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 30676
Exam code: midterm02SpsR
p: 27 students
r: 4 students
t: 5 students
v: 3 students
x: 2 students
y: 0 students
z: 0 students

A sample "p" response (from student 7563):

Astronomy midterm question: possible IAU classification of "twotino" 2002 WC19?

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

A "twotino" is defined as a Kuiper belt object whose orbit around the sun is periodically perturbed by Neptune's gravity[*]. Discuss whether or not a "twotino" such as 
2002 WC₁₉ (shown at right[**], as depicted by an artist) could be considered a dwarf planet, and why. Explain using the International Astronomical Union classification scheme.

[*] wiki.pe/Twotino.
[**] se-database.fandom.com/wiki/2002_WC19.

Solution and grading rubric:

• p:
  Correct. Discusses IAU classification scheme to argue that 2002 WC₁₉ would meet qualification I (orbits the sun directly), and appear to meet qualification II (rounded shape), but does not meet qualification III (dominates its orbit), it would be classified as a dwarf planet.
• r:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
• 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 only tangentially related to the IAU classification scheme.
• 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 30674
Exam code: midterm02nwF7
p: 19 students
r: 1 student
t: 7 students
v: 4 students
x: 2 students
y: 0 students
z: 0 students

A sample "p" response (from student 2815):

Astronomy in-class activity: planet classification schemes

Astronomy 210 In-class activity 12 v.13.06.10, fall semester 2013
Cuesta College, San Luis Obispo, CA

Students find their assigned groups of three to four students, and work cooperatively on an in-class activity worksheet to discuss the evolution of how planets are categorized, and how to implement the current International Astronomical Union classification scheme to categorize different solar system bodies.





Some samples of student responses (fall semester 2008) to question 2(h) ("Discuss a plausible motivation for why it was necessary to revise the definitions of planets in the 1860s and in 2006") are given below. Students in each group are referred to by a confidential four-digit identification number.

Many responses discussed the narrowing of the planet definition in order to exclude a "multitude" of planet candidates:

"We were getting too many planets, in 1860 there were 200+ large bodies and in 1992-present there were [approximately 1,300+] bodies."
--0013, 1327, 4245

"Because of the massive amounts of large bodies that would have been considered planets."
--0217, 0911, 1186

"Because there were too many."
--1208, 3248, 9387

"[A lot of] planets are a lot of planets to track. If the large bodies in the Kuiper belt count why don't the bodies in-between Mars and Jupiter of the same size count?"
--3273, 3903

"Because of new discoverys [sic] of 'bodies' so they had to limit the definition of what an actual planet could be."
--1990, 2580

"Without the definitions it would include [too many] large bodies and that would be way too many."
--4555, 9259

"There are too many 'planets' like Pluto in the outer solar system."
--3912, 5805

Some other groups also discussed other plausible motivations, in addition to limiting the number of potential planets:

"They would be hard to determine because they haven't cleared their orbit even though they do have a shape 'rounded out' by gravity. It would be hard to study because there a lot."
-3089, 4207, 7120

"Because it would be hard to have an accurate scale to compare any two 'planets.' So thus limiting the requirements makes comparisons easier."
--2639, 4127, 8187

"The definition was too wide including objects that were extremely different from each other."
--2020, 8808

"Too many bodies to classify. Easier to maintain."
--0805, 7776

"Too many variations between [planets], too many planets. Needed new scientific classifications."
--1988, 5389

Other groups discussed other reasons, but still received full credit for their responses:

"The advancement of technology gives us more accurate ways of classifying our solar system."
--1307

"We want to explore the universe and classify it."
--4018, 6586, 5997

Presentation: planets(?)

Blink, and you'll miss Pluto! These are negative exposures of the same region of the night sky two weeks apart in a blink comparator at the Lowell Observatory in Flagstaff, AZ, illustrating the discovery of the planet Pluto in 1930 (arrows were drawn in later). (Video link: "120104-1290088.")

More recently, Pluto has been demoted from its planet status. Many people are not happy about this.

And apparently neither is Pluto.

In this presentation we will go over the basis for classifying planets (and non-planets) in the solar system, which you will apply in the subsequent in-class activity.

First, the original and then the most recent definitions for planets.

Recall that Greeks referred to "wanderers" making prograde/retrograde loops in the night sky as "planets," as observed over many nights. There were five planets visible to the naked eye back then: Mercury, Venus, Mars, Jupiter, and Saturn. (Why wasn't Earth considered a planet back then?) Subsequent re-definitions over time would result in more or fewer numbers of planets, which will be discussed in the in-class activity.

The most recent classification scheme was adopted by the International Astronomical Union in 2006, and can be considered a list of three questions to be answered either "yes" or "no" for a solar system object. At any point a question is answered "no," then the object is immediately classified, but if all three questions are answered "yes," then the object is classified as a planet.

First question: does the object orbit the sun directly? If "no" because it is orbiting something else orbiting the sun, then the object is classified as a moon or satellite. If "yes" to orbiting the sun directly, then the object proceeds to the second question.

Second question: does the object have a rounded shape, that is, was there enough mass such that it retained enough formation heat to melt itself, and enough gravity to form itself into a rounded shape? If "no" because it has a "lumpy potato" shape because it didn't have enough heat and gravity to round itself out, then the object is classified as solar system debris. If "yes" to having a rounded shape, then the object proceeds to the third and final question.

Third question: does the object dominate its orbit, that is, does it have enough mass compared to everything else in its vicinity to pull in or eject all other objects that share or cross its orbit? If "no" because it shares its orbit with many other similar objects, then the object is classified as a dwarf planet. If "yes" to dominating its orbit, then the object is classified as a planet.

Second, let's apply the IAU classification scheme to various solar system objects.

Earth's moon, which we'll rotate to get a better sense of its shape. Does it orbit the sun? Does it have a rounded shape? Does it dominate its orbit? Based on the answers to these three questions, the moon must be classified as a __________.

Ceres (located in the asteroid belt), which we'll rotate to get a better sense of its shape. Does it orbit the sun? Does it have a rounded shape? Does it dominate its orbit? Based on the answers to these three questions, Ceres must be classified as a __________.

Toutatis (also located in the asteroid belt), which we'll rotate to get a better sense of its shape. Does it orbit the sun? Does it have a rounded shape? Does it dominate its orbit? Based on the answers to these three questions, Toutatis must be classified as a __________.

Mars, which we'll rotate to get a better sense of its shape. Does it orbit the sun? Does it have a rounded shape? Does it dominate its orbit? Based on the answers to these three questions, Mars must be classified as a __________.

Amalthea (in orbit around Jupiter), which we'll rotate to get a better sense of its shape. Does it orbit the sun? Does it have a rounded shape? Does it dominate its orbit? Based on the answers to these three questions, Amalthea must be classified as a __________.

Pluto (located in the Kuiper belt), which we'll rotate to get a better sense of its shape. (This simulation represents the limits of resolvability, even with the best telescopes.) Does it orbit the sun? Does it have a rounded shape? Does it dominate its orbit? Based on the answers to these three questions, Pluto must be classified as a __________.

Although Mercury is classified as a planet, we include it here for comparison to the five known dwarf planets: Pluto, Eris (also in the Kuiper belt), Ceres, Haumea (which is somewhat flattened out due to its rapid rotation, but still "round enough"), and Makemake, the last two also in the Kuiper belt. (Why is Mercury a planet instead of a dwarf planet?) There may be twelve to twenty other asteroids and Kuiper belt objects that would be sufficiently round enough to be considered dwarf planets, but their true shapes have not yet been determined.

In the subsequent in-class activity you will discuss the history of planetary classification schemes, and implement the current International Astronomical Union classification scheme to categorize different solar system bodies.

Astronomy in-class activity: planet classification schemes

Astronomy 210 In-class activity 24 v.11.05.04 (revised), spring semester 2011
Cuesta College, San Luis Obispo, CA

Students find their assigned groups of three to four students, and work cooperatively on an in-class activity worksheet to discuss the history of planetary classification schemes, and implement the current International Astronomical Union classification scheme to categorize different solar system bodies.



Previous post:

• Astronomy in-class activity: planet classification schemes (fall semester 2008).
  Previous worksheet version, with sample student remarks on plausible reasons for redefining planets.

Astronomy final exam question: Earth in Kuiper belt?

Astronomy 210 Final Exam, fall semester 2010
Cuesta College, San Luis Obispo, CA

[20 points.] In an open letter to the 27th International Astronomical Union General Assembly, an amateur astronomer advocated against Pluto's planet demotion:

"If Earth were in Pluto's orbit, according to [the IAU classification scheme], it would not be considered a planet either."
--Laurel E. Kornfeld, http://laurele.livejournal.com/10429.html, August 6, 2009.

Decide whether this statement is correct or incorrect, and how you know this. Explain using the International Astronomical Union classification scheme.

Solution and grading rubric:

• p = 20/20:
  Correct. Pluto only satisfies the first two of the three requirements (orbits the sun, has a rounded shape, cleared/dominates its orbit) to be a planet. The online comment could either be considered incorrect or correct, depending on whether Earth would be able to dominate or not dominate Kuiper belt objects near its new orbit (the degree of which is beyond the scope of this course).
  
• r = 16/20:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Discussion of IAU requirements, or why online comment is incorrect/correct is not clear.
  
• t = 12/20:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. Problematic discussion of IAU requirements and why online comment is incorrect/correct.
  
• v = 8/20:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Discussion of criteria only tangentially related to the IAU requirements.
  
• x = 4/20:
  Implementation/application of ideas, but credit given for effort rather than merit. Discussion of criteria unrelated to the IAU requirements.
  y = 2/20: Irrelevant discussion/effectively blank.
  
• y = 2/20:
  Irrelevant discussion/effectively blank.
  
• z = 0/20:
  Blank.
  

Grading distribution:
Section 70158
p: 30 students
r: 7 students
t: 2 student
v: 2 students
x: 1 student
y: 0 students
z: 1 student

A sample "p" response (from student 3272), discussing how the statement is incorrect:

A sample "p" response (from student 2369), discussing instead how the statement is correct:

A sample "p" response (from student 1234), recognizing that the statement may be correct or incorrect, but more information is needed to determine the extent of Earth's influence on Kuiper belt objects:

Astronomy final exam question: Interpreting IAU classification of Pluto

Astronomy 210 Final Exam, Fall Semester 2010
Cuesta College, San Luis Obispo, CA

[20 points.] An astronomy question on an online discussion board (http://answers.yahoo.com/question/index?qid=20060816202219AA5qzCL) was asked and answered:

ne0aes0p: Why is Pluto not a planet anymore?

crown1114: Well, because based on [the IAU] definition of a planet, Pluto...satisfies only 1 criteria and according to them, 2 criteria must be satisfied in order to be called a planet.

Discuss whether this statement is correct or incorrect, and how you know this. Explain using the International Astronomical Union classification scheme.

Solution and grading rubric:

• p = 20/20:
  Correct. The online comment is incorrect, as Pluto needs to satisfy three requirements (orbits the sun, has a rounded shape, cleared/dominates its orbit) to be a planet, of which only the first two are actually satisfied.
  
• r = 16/20:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Discussion of IAU requirements, or why online comment is incorrect is not clear.
  
• t = 12/20:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. Problematic discussion of IAU requirements and why online comment is incorrect.
  
• v = 8/20:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Discussion of criteria only tangentially related to the IAU requirements.
  
• x = 4/20:
  Implementation/application of ideas, but credit given for effort rather than merit. Discussion of criteria unrelated to the IAU requirements.
  
• y = 2/20:
  Irrelevant discussion/effectively blank.
  
• z = 0/20:
  Blank.
  

Grading distribution:
Section 70160
p: 25 students
r: 5 students
t: 4 students
v: 1 student
x: 2 students
y: 0 students
z: 1 student

A sample "p" response (from student 7133), successfully applying a recreation of the IAU classification flowchart from memory:

Another sample "p" response (from student 9890), with a personal opinion regarding Pluto:

Another sample "p" response (from student 0802), with another personal opinion about Pluto, and kudos for the instructor:

Astronomy final exam question: IAU classification of Pluto and asteroids

Astronomy 210 Final Exam, Spring Semester 2010
Cuesta College, San Luis Obispo, CA

[20 points.] According to the "Friends of Pluto," Pluto has been downgraded to an asteroid. Explain why Pluto and asteroids are each placed in different categories under the International Astronomical Union classification scheme.

(Photo credit: harlanm, "Eyewitless News: Save Pluto" contest, http://www.worth1000.com/emailthis.asp?entry=312604).

Solution and grading rubric:

• p = 20/20:
  Correct. Asteroids satisfy only the first IAU planetary requirement --that they orbit the sun--and because of their irregular shape, and their shared, non-dominating orbits, are classified as solar system debris. Pluto satisifes the first IAU requirement as well as the second (being rounded in shape), but because it does not dominate its orbit, is classified as a dwarf planet.
  
• r = 16/20:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
  
• t = 12/20:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. Problematic discussion, but at least understands IAU classification scheme. May discuss how asteroids and Pluto are different from the planet category, and/or placing them in the same non-planet category.
  
• v = 8/20:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Only partial understanding of IAU requirements.
  
• x = 4/20:
  Implementation/application of ideas, but credit given for effort rather than merit. Discussion of criteria unrelated to the IAU requirements.
  
• y = 2/20:
  Irrelevant discussion/effectively blank.
  
• z = 0/20:
  Blank.
  

Grading distribution:
Section 30674
p: 18 students
r: 1 student
t: 13 students
v: 7 students
x: 0 students
y: 1 student
z: 0 students

Section 30676
p: 23 students
r: 3 students
t: 15 students
v: 9 students
x: 14 students
y: 4 students
z: 0 students

A sample "p" response (from student 7272):


Another sample "p" response (from student 2569):


A terse sample "p" response (from student 1415):


A sample "p" response (from student 7615), insulting the intelligence of asteroids:


A sample "p" response (from student 1105), with a sad Pluto:


A sample "v" response (from student 1825), placing Pluto in the asteroid belt:


A sample "x" response (from student 4000):


A sample "y" response (from student 8282), with a commonly-held sentiment: