Q: Why are the outer planets of the Solar System so much more massive than the inner planets?

A: By the central limit theorem, everything eventually appears to look like a Bell curve. Therefore planet masses increase with distance to the Sun before decreasing, and the planets at the end of the distribution (Mercury & Pluto) have small masses while the planets in the middle (Jupiter) have large masses.

One doesn't need to know anything about astronomy or planetary formation to know this answer is nonsense. Furthermore, the student should have known that Pluto isn't a planet (Mars is also less massive than both the Earth and Jupiter, and Neptune is more massive than Uranus as well, breaking the trend).

On the other hand, it's funny nonsense. Funny nonsense has gotten immortalized as internet jokes, and if the joke is to be believed, even led to an 'A' for the student. There's even a journal for funny research.

Is it ethical to award a few points for this answer?

  • This extended discussion has been moved to chat. Please read this FAQ before posting another comment. – Massimo Ortolano Nov 3 '20 at 19:18
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    what is the real/physical answer to this? :) – Ben Nov 4 '20 at 6:38
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    @Ben it has to do with the so-called frost line - en.wikipedia.org/wiki/Frost_line_(astrophysics). Beyond this line the temperature is cold enough for volatile compounds to form solids. Within this line only rocks remain solid (hence all four inner planets are rocky), beyond this line the volatile compounds can accrete and form gas giants. – Allure Nov 4 '20 at 7:08

Is it ethical to award a few points for this answer?


It does not demonstrate understanding. If I wrote a good-intentioned, but poor answer and got the same amount of points, I'd be peeved.

  • This answer led to some debate, which has been moved to chat; let us remember to be nice. – cag51 Nov 2 '20 at 20:01
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    I'm expecting an answer like "it is unethical because <course of events> leads to <someone being harmed>" not "it' unethical because it makes me feel peeved" or "it's unethical because it's not in my rubric." Your feelings and grading criteria are preferences, not ethical matters. – Anonymous Physicist Nov 3 '20 at 1:20
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    @AnonymousPhysicist the answer could easily be expanded to address your concern. If students are awarded passing grades for being funny while demonstrating a complete lack of understanding of the subject matter, that harms the students who did understand the subject matter, by devaluing their own grade. It will harm them much more directly if there is any kind of quota or scaling of grades based on average performance. They would be justifiably peeved, because it does actually hurt them. – Nathaniel Nov 3 '20 at 4:54
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    @AnonymousPhysicist: The question is of the form “Is [this pedagogical action] ethical?” So it seems pretty reasonable that answers are addressing the question “Is it good pedagogy?” and leaving implicit the step “following good pedagogy is generally ethically good”, since this last step is uncontroversial and is nothing to do with this specific question. – PLL Nov 3 '20 at 11:40
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    It's definitely about ethics. If someone is inappropriately rewarded, the efforts of the honest and industrious students are devalued. – Dominic Cronin Nov 3 '20 at 11:57

I tend to give at least 1 point out of 10 for almost anything that could be construed as being relevant to the question.

Compared to the responses I tend to give 1/10 for, this is better in several regards:

  • It has a logic to it.
  • The writer obviously knows it is wrong.
  • The writer demonstrates knowledge of something (in this case normal distributions).
  • The writer demonstrates some intellectual creativity.

It depends somewhat on my standards for partial credit on the problem, but I'll probably give a good coherent joke response 3/10. On occasion it might be 2/10 if I feel like I need to reserve 3/10 for slightly correct responses that are less good than some responses I'm giving 4/10 for.

Let's face it - awarding of partial credit isn't perfectly accurate, and any numerical score I give has an error bar of a few percent. (Almost always, the central limit theorem works and the errors mostly cancel out rather than stacking up, leaving still a few percent error.) I think it's fine to put a thumb on the noise here.

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    I used to do this as well, until I realized that this just trains students to spout random nonsense (or, in the case of home exams, google for Wikipedia definitions) if they have no idea what the actual answer is. I'm now pretty strict about "is this an answer to the actual question" when evaluating freetext answers. – xLeitix Nov 2 '20 at 9:56
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    @xLeitix, note that the OP seems to be presenting an exceptional case, not the norm. So I don't see the issue of encouraging bad behavior. – Buffy Nov 2 '20 at 12:46
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    @xLeitix: The general ability to figure out what nonsense is vaguely relevant is more valuable than any specific fact from my courses. – Alexander Woo Nov 2 '20 at 15:49
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    @xLeitix People often complain that colleges don't prepare students for the real world, in which spouting nonsense is how you succeed. – Studoku Nov 2 '20 at 16:33
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    I like this answer, but don't share your confidence that "[t]he writer obviously knows it is wrong." – John Coleman Nov 3 '20 at 13:17

It depends on what form of ethics you are following.

Virtue ethics? Truth is a virtue; this answer is not true, so to reward it as though it was the truth is dishonest and unethical. Your job is to reward truthful answers, not funny ones, so you would be in dereliction of your duty.

Hedonic ethics? What matters is making people happy. Giving the student extra marks will make him happy, but if the students who gave more accurate answers find out, it will make them all unhappy. Allowing that to happen would be unethical. Therefore we must consider whether they are likely to find out...

Kantian deontological ethics? What if every examiner always gave points for funny answers? It would create a situation where the ability to tell jokes was more useful for achieving qualifications than studying. This would be bad for society. Therefore, this is unethical.

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    Is it ethical to upvote this answer because it's funny, rather than because it's helpful? – Robyn Nov 3 '20 at 22:17
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    @Robyn Your comment, however, is both funny and valid, so take an upvote. – val says Reinstate Monica Nov 4 '20 at 10:34
  • Your answer is premised on the assumption that the creation of original and successfully humorous content is easier than simply spitting back the prescribed answer to a question. This is not only unsupported, but intuitively we can see that it is almost certainly false. The supposed slippery slope, therefore, where rewarding humor will result in everyone everywhere simply joking their way through PhD programs is absurd in the extreme. In fact, being able to successfully make someone laugh using the material from the class may well show a greater grasp of it than parroting an answer. – iconoclast Nov 8 '20 at 19:00

It is possible that the student believes it to be correct (I don't know the student or his/her typical performance). Treating a serious but wrong answer as a joke could be insulting to the student who sees the feedback.

Either way, you can give written feedback in addition to a grade. Even if the answer does not deserve points, you can leave comments on it for the student.


It's fine if the question is already getting undeserved partial credit. Otherwise it doesn't seem very professional. I usually write a very small 0 (a big 0 feels like "how dare you disrespect my test -- you get a ZERO, with extreme prejudice!")

Sometimes many other people are getting undeserved partial credit on the same Q with "write anything to try to get some credit" answers. Realistically those are worth 0, but often get 2/10 for the barely relevant parts they threw in by mistake. Esp if TA's are grading. Essentially, the Q has 2 free points. It seems fair to give a joke answer those same 2. If someone calls you on giving 2 points for a joke you can tell them, in nicer words "the joke showed as much understanding as the other answers worth 2".

A joke answer is the same thing as "I don't know". It's better than a blank page (you don't have to wonder if the student didn't see it, and might want to make it up since their test was sticky or something). You're not rewarding a joke -- you're appreciating honesty and not wasting your time.

But if a student completely skips a Q, doesn't even know how to start it, the rest of their scores are often a mess, too. They know they're not passing the class and it makes no difference what score you give it. Giving them 3/10 is just a nice "I don't hate you for failing my class" gesture.


My interpretation would be that they didn't know the accepted answer, and so tried to use their physics intuition to invent a theory of solar system formation on the spot. It seems they came up with something similar to Laplace's collapsing rotating dust cloud, and as a hypothesis for why this dust cloud is thicker in the middle and thin at the inner and outer extremes, the random collisions of particles in the cloud resulting in a Normal distribution is at first glance a plausible guess.

There are two aspects to this on which you could assign marks. Were they able to recite the memorised textbook answer they were told to learn? Not knowing the answer, were they able to invent a valid physical theory of their own to explain it? The latter is a much more sophisticated question. To judge it, one would need to know how much they knew about the solar system that their theory has to explain.

This would seem like a perfect opening to start a conversation about the history of early theories of solar system formation, the features they had to explain, new research on extrasolar planets, and point them towards physical reasoning, not just the rote memorisation of facts. If you put yourself in the place of Descartes or Laplace, how would you develop a physics-based explanation? That's an important skill too, and ethically you can and should judge them on how well they did it.

I'd not take off any points for calling Pluto a planet - from the point of view of discussing the physics of solar system formation, the distinction is not material. And minor exceptions to the general trend of masses might be explained by random variation. Small-sample histograms of the Normal distribution are often irregular. Are there stronger objections to their theory that they ought to have known about?

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  • +1, the funny response could be a knee jerk reaction to exceedingly vague question. i.e. a especific answer to a very generic question. As a physicist I hate these kind of questions. A better question could be "Why are the outer planets of the Solar System at least 1000 times more massive than the inner planets?". Perhaps the OP is looking for a standard answer and the student's awareness of it. In this case use "Why the astronomical community agrees that...". Imagine what kind simplified answers to this question could ALSO explain erroneously situations of planets billions of times larger! – alfC Nov 4 '20 at 20:51

Maybe I can give some insight as I am a student who gives such answers quite regular and quite regular earns some points for it.

The impact you create usually is quite low. Assuming you, as most people do, only grant a very small, near insignificant amount of points. Most of my exams have 120 points (for 120 mins) and if I earn Points for such answers it is not much. I would say a Median of 1 and a max of 3. Overall exams, I earn maybe an average of 0.2 (0,16%) points per exam maybe less. This also means that my peers usually aren't even interested enough in it to try it themselves. The best it usually does is making a good anecdote. I also would like to compare it to missed points in exams, which I was supposed to get but didn't, I spot an average of ~3 (2,5%) per exam.

To finally answer your question. Yes, sure, it can be ethical, but it deepens wich ethic you would consider. The negative impact it usualy has is quite low and therefore the threshold to make it ethical is as well.

The last thing, I think what you should ask yourself as well is: Does it encourage better learning, which is I think a hard to answer the question. But for me personally, it did.


A free form question to be answered by many students ideally has a grading rubric, otherwise it is next to impossible to keep grading consistent across graders and over time, not even within a single batch of tests. The rubric will generally not intersect with the unexpected joke.

Supposing I own the rubric alone: the joke will generally not be worth the effort to adapt the rubric to accommodate that kind of answer with a non-zero score (and maybe re-grade previous answers accordingly). The comical effect will wear off before this is accomplished.

I'd go with zero points and a smiley, unless I can honestly construe parts of the answer as demonstrating particular items in the rubric I'm applying.


If the awarding of points to such a student doesn't disadvantage other students in any way, then sure, it is fine to do it. The only problems occur if another person suffers in some way because of it.

And, assuming that this is a real case and not made up, it is possible that the person awarding the points has some information that the student knows a better answer (I certainly don't) and is just having a bit of fun.

Ideally, grading is of individuals, not groups. The grade of an individual student is based entirely on what that student does, not in any way on what the class as a whole (or worse, classes in the past) do. There is no predefined distribution that grades are forced to adhere to. I'm happy if every student gets full marks. If they all get zeros I'm not happy, but I know what must be done, at least. If you keep that principle at the front then lots of such questions become moot.

Of course, another issue is whether awarding those points helps that student or hurts them. Giving good grades because of, for example, hair color, would be wrong because it doesn't contribute to the learning process of the student. But I see no such harm here. It is a discrete event.

Hmmm. Is it because the gas giants sweep out a larger circumference and hence picked up more material from the primordial gas cloud? Just guessing.

And the status of Pluto is just a judgement call.

  • This seems to wander, a lot. How does all students getting high or low grades relate to joke answers? In the 2nd para, are you saying you give points if the written answer is bad, but you "know" the student knows it? The hair color example seems odd -- are you saying that since anyone can write something funny for more credit, it's fair? – Owen Reynolds Nov 2 '20 at 21:37
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    @OwenReynolds I'm trying here to make the point that this question about awarding "a few points" to a student is unethical is if it would affect the grades of other students. This could happen with competitive grading and with many things called "grading on the curve". I don't say that I do this. I say that it isn't, on its face, unethical unless it affects others or is for personal reasons unrelated to learning (e.g. hair color). This case may not be "best practice" but it isn't unethical unless others suffer. – Buffy Nov 2 '20 at 21:50
  • @Buffy if a student pays a bribe to a professor in return for a good grade, would you say that that is ethical if “it doesn’t disadvantage other students in any way”? That is obviously the wrong criterion. What about the employers who are disadvantaged by thinking the person they will be hiring knows more than he or she really does? The customers of that employer? Or the student him/herself who gets the message that paying bribes (or telling jokes) is a much easier way to get ahead in life than honest, hard work? Grading decisions have many consequences which this answer completely ignores. – Dan Romik Nov 4 '20 at 15:35
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    @DanRomik. " if a student pays a bribe..." is hardly in the same league. Why make this about something more than it is? A few points on one question on one exam isn't going to have any overall effect on employers, etc. It isn't the medical board exam, for example. Why do you assume that the student is somehow lazy? You are making a "federal case" out of a joke. You aren't usually so unreasonable. – Buffy Nov 4 '20 at 15:50
  • @Buffy I’m saying that the reason you cited for why it’s “fine”, namely that it “doesn’t disadvantage other students”, isn’t by itself sufficient to explain why it’s ethical. The bribe example illustrates that. I’m not saying that giving points for a joke answer is as bad as doing it in exchange for a bribe, but rather that a helpful answer would provide reasoning sufficient to differentiate between those two actions. – Dan Romik Nov 4 '20 at 15:58

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