Pluto Isn't Even A Planet?! What?!

[The Random NPC]

There is a reason for this (or, at least, there was in my day...) - it is called "Showing your work". A question in an exam earns a number of marks - you will get one mark for the correct answer, and another mark for all the steps in the working out. The other points are there to show that you understand how you get to the answer.

So, in a 5-point question, going straight to the answer would earn you exactly one point. Conversely, if you get all the steps in the working out, but goofed on the final answer you would have gotten 4 out of 5 points.

That isn't always the case, I've had a few exams (mostly in high school) where the question was worth 1 point. If you didn't show your work you didn't get the point. If you got the answer wrong, you also didn't get the point. That isn't even getting into why you need to show your work.

[jayem]

That isn't always the case, I've had a few exams (mostly in high school) where the question was worth 1 point. If you didn't show your work you didn't get the point. If you got the answer wrong, you also didn't get the point. That isn't even getting into why you need to show your work.

And the final option, there were quite a few exams where you'd get:
5 points if you just got straight to the right answer
0 points if you got straight to the wrong answer
5 points if you did the working out to the right answer
3 points if you did the working out but messed one sign up.

Which even though it doesn't explicitly demand working out, makes it a sensible investment (unless there are time constraints or you are very confident)

[Vinyadan]

My idea is better than all of yours. We should call the stars fixed stars, because they all move together in the sky as if they were fixed to a dome. Then we call the things that move autonomously planets, that's a Greek word that means wanderer. As for the invisible things that lurk and move in the impenetrable darkness beyond the stars, and that vaster and more appalling universe of dim entity and consciousness which lies deeper than matter, time, and space, and whose existence we suspect only in certain forms of sleep- those rare dreams beyond dreams which come never to common men, and but once or twice in the lifetime of imaginative men, well, the cosmos of our waking knowledge, born from such an universe as a bubble is born from the pipe of a jester, touches it only as such a bubble may touch its sardonic source when sucked back by the jester's whim.

[PhyrexianShovel]

And the final option, there were quite a few exams where you'd get:
5 points if you just got straight to the right answer
0 points if you got straight to the wrong answer
5 points if you did the working out to the right answer
3 points if you did the working out but messed one sign up.

Which even though it doesn't explicitly demand working out, makes it a sensible investment (unless there are time constraints or you are very confident)

Yeah, many teachers I've had used this system. It usually seems to work, because if you already clearly know the answer, you get full points, but if you're not able to do it quickly, it becomes worth working out on paper.

[halfeye]

And the final option, there were quite a few exams where you'd get:
5 points if you just got straight to the right answer
0 points if you got straight to the wrong answer
5 points if you did the working out to the right answer
3 points if you did the working out but messed one sign up.

Which even though it doesn't explicitly demand working out, makes it a sensible investment (unless there are time constraints or you are very confident)

There are exams which aren't on a time limit?

If you've got a choice between putting down five right answers for 25 points, and putting down one answer with full working for five points and three points if you messed something up, you've got to be pretty sure you haven't got any hope of getting four out of five right before putting down your working out pays off. The way to do it is to put down all the answers, then come back around and fill in as much working out for as many questions as you can in the time available, supposing there are exams where you get full marks for correct answers with no working out, I don't remember any but it was a long time ago.

I don't care very much what we call Pluto, but the reasons given (i.e. the working out) for the current description is very silly, and I don't like silly reasons for descriptions.

[Algeh]

There are exams which aren't on a time limit?

If you've got a choice between putting down five right answers for 25 points, and putting down one answer with full working for five points and three points if you messed something up, you've got to be pretty sure you haven't got any hope of getting four out of five right before putting down your working out pays off. The way to do it is to put down all the answers, then come back around and fill in as much working out for as many questions as you can in the time available, supposing there are exams where you get full marks for correct answers with no working out, I don't remember any but it was a long time ago.

I don't care very much what we call Pluto, but the reasons given (i.e. the working out) for the current description is very silly, and I don't like silly reasons for descriptions.

I break my math tests into two sections: one with "just grading the answer" questions (which are sometimes even multiple choice) and one with "show your work and explain your process" questions. They only have to show detailed work on 2 questions, but I hold them to pretty high standards of work-showing on those. (They also have to write out an explanation in words of what they did.) It's a pretty good compromise since I can put the basic "do you have this particular skill?" questions in the first part of the test and the bigger "can you put it all together?" questions on the second part.

I don't put time pressure on students during tests, but I'm lucky to be in a situation where I can have test-takers for a long enough chunk of time for the slower workers to finish but let the early finishers leave as soon as they're done.

[Knaight]

There are exams which aren't on a time limit?

There's time limits and there's meaningful time limits. There's plenty of exams which don't have the latter.

Lets be honest, did anyone in this thread not have a big block of time to check answers and/or kill time after each section on the ACT, SAT, or other similar national test? For reasons other than being from a country that didn't use on at the time they were in high school.

[warmachine]

Arguing over whether Pluto is a dwarf planet? Meh. I agree with Leah Crane's article in New Scientist and we should cull the number of moons. The solar system has too many moons – it's time for a cull. We've found all the proper moons around Saturn, for example, and now we're just finding misshapen rocks. Demote Daphnis to 'moonlet'.

[Chronos]

Personally, I think everyone should be proud of Pluto's new recognition. Back when Pluto was considered a planet, it was very much the ugly duckling of the Solar System: It was much smaller than even Mercury, it's the only one with an icy rather than rocky or gassy composition, it's the furthest out, its eccentricity and orbital inclination are much, much greater than any of the others, and so on. It never actually fit in with the other planets.

Now, however, that it's recognized as a Kuiper belt object, it's a prince of its category. It's not quite the largest or closest of them, but it's very near the top of both of those lists. Its composition is now perfectly normal, and it has one of the more regular orbits.

And personally, I think that the whole category of "planet" is silly, anyway. Earth has a lot more in common with Luna or Ceres than it does with Jupiter. We should have three separate categories for rockballs (Mercury, Venus, Earth, Luna, Mars, Ceres), gasballs (Jupiter, Saturn, Uranus, and Neptune), and iceballs (Eris, Pluto, Quaoar, Sedna, and all their myriad kin).

[Silverraptor]

For me, this is how I understand it. Planets have a stable relatively equal orbit around a star and a moon is a smaller celestial body that orbits around one of these planets in a stable orbit. For Pluto, I see it that since it has a rather elongated orbit that has it cross several other planet's orbit and can change what position it is in our solar system based upon where it is in the orbit, I'm fine with the new definition of it not being a full fledged planet.

Essentially, a dwarf planet, by definition, means that it is a celestial object that fits a number of criteria to almost be considered a planet, but doesn't meet all of them so it falls short. Similar to the sense of logic where a virus is technically classified as "not alive" because it only fits 5 of the 7 characteristics of life. So it's something that is almost a planet, but just falls short.

Or alternatively:

[AvatarVecna]

That like saying Tomatoes isn't even a vegetable but fruits.

Botanically, there's no such thing as a "vegetable". It's purely a matter of cooking - taste, essentially. Tomatoes are botanically fruits, but they are used less like botanical vegetables in cooking and more like "vegetables".

[hamishspence]

And personally, I think that the whole category of "planet" is silly, anyway. Earth has a lot more in common with Luna or Ceres than it does with Jupiter. We should have three separate categories for rockballs (Mercury, Venus, Earth, Luna, Mars, Ceres), gasballs (Jupiter, Saturn, Uranus, and Neptune), and iceballs (Eris, Pluto, Quaoar, Sedna, and all their myriad kin).

Ceres now appears to rather icy - perhaps "iceball" might be a better description than "rockball":

https://en.wikipedia.org/wiki/Ceres_(dwarf_planet)

Origin and evolution
Ceres is a surviving protoplanet (planetary embryo) that formed 4.56 billion years ago, the only one surviving in the inner Solar System, with the rest either merging to form terrestrial planets or being ejected from the Solar System by Jupiter.[118] However, its composition is not consistent with a formation in the asteroid belt. It seems rather that Ceres formed as a centaur, most likely between the orbits of Jupiter and Saturn, and was scattered into the asteroid belt as Jupiter migrated outward.[16] The discovery of ammonia salts in Occator crater supports an origin in the outer Solar System.[119]


https://en.wikipedia.org/wiki/Plutoid

Analogous terminology
Before the Dawn mission, Ceres was sometimes called a terrestrial dwarf to distinguish it from the ice dwarfs Pluto and Eris. However, since Dawn it has been recognized that Ceres is an icy body closer to the icy moons of the outer planets than it is to the terrestrial planets.[13][14]

[halfeye]

Yeah, Ceres is an iceball for sure, as is Hygiea, calling the iceballs "comets" seems fair too, they would emit gas if they got much closer to the sun.

[Aedilred]

The problem is this. If Pluto is a planet, so are 20 other bodies in the solar system that we know of, and probably hundreds. Do you want to memorize a list of 200 planets?

I have been told by astronomers - who I don't think were joking - that this was actually a serious factor in the decision to "demote" Pluto. When clarifying the definition of planet, there was essentially a choice between Pluto's retaining its status and a bunch of other bodies being promoted, or demoting Pluto.

In the absence of any other entirely decisive basis for going one way or the other, maintaining a short and familiar list was thought to be more accessible and thus more in the interest of the science, than a longer one which would be harder for children and laypeople to learn and remember.

Not true, because fruits are not plants--they're *parts* of a plant (specifically, the seed-bearing structure in flowering plants). Tomatoes are technically a fruit because they follow that biological definition, entirely independently to what they're considered to be cooking terms.

I think the point is not that tomatoes are not fruit, but that "vegetable" itself is a meaningless term.

Fruit is a part of a plant, like the root, stem, leaf, etc. No arguments there. The tomato is the fruit part of a tomato plant, also no argument. So a tomato is a fruit.

But when we consider vegetables, well... Courgettes/zucchini are fruit. Spinach is a leaf. Parsnips are roots. Celery is a stem. We also eat flowers and seeds. We eat all different parts of plants and lump almost all of them under the heading of "vegetable".

The confusion only comes because we've developed a separate culinary category for sweet fruit... not all of which are actually fruit, come to that (rhubarb) and some smart-aleck decided that this was mutually exclusive with "vegetable" - and therefore that you could score points by going "actually the tomato is a fruit, not a vegetable", ignoring that that's a largely meaningless distinction, that the distinction is in any case use-based and on that basis tomatoes are arguably more vegetable than fruit, and that there's a whole bunch of other fruit that's unquestionably classed as "vegetable" already.

So yes, tomatoes are fruit. That doesn't mean they're not vegetables.

[DavidSh]

These days, the vast majority of known planets orbit other stars than the Sun, and we aren't expected to have memorized their designations. I don't expect memorable names for any of these unless we either manage to send an interstellar probe, or detect life by whatever means.

[snowblizz]

In the absence of any other entirely decisive basis for going one way or the other, maintaining a short and familiar list was thought to be more accessible and thus more in the interest of the science, than a longer one which would be harder for children and laypeople to learn and remember.

Poppycock. That may be the dumbest argument I've ever seen. And insulting to people in general. Most people don't spend much learning names of the planets. And I bet the vast majority of the population of this planet do not call them by the names the IUA claims are official either.


It's scientific pedantry of the highest order. It's moves like that which causes Ivorytower comments.


There is and was no particular need to name planets or include or disclude anything from the Classic Planets (tm) list. Noone cared or had any idea or issue with there being multiple objects that might actually in some ways be like Pluto except they aren't because then reasonably they'd been in the original list.

As Varsaavius said, the classics are classics for a reason.

[Fyraltari]

These days, the vast majority of known planets orbit other stars than the Sun, and we aren't expected to have memorized their designations. I don't expect memorable names for any of these unless we either manage to send an interstellar probe, or detect life by whatever means.

These are called "exoplanets", technically speaking.

[Strigon]

Poppycock. That may be the dumbest argument I've ever seen. And insulting to people in general. Most people don't spend much learning names of the planets. And I bet the vast majority of the population of this planet do not call them by the names the IUA claims are official either.


It's scientific pedantry of the highest order. It's moves like that which causes Ivorytower comments.


There is and was no particular need to name planets or include or disclude anything from the Classic Planets (tm) list. Noone cared or had any idea or issue with there being multiple objects that might actually in some ways be like Pluto except they aren't because then reasonably they'd been in the original list.

As Varsaavius said, the classics are classics for a reason.

The thing is, planet is an arbitrary distinction. It always will be, no matter what they do. In this case, they chose an arbitrary distinction that was clearly defined, and almost entirely consistent with what had been done before. Unfortunately, they couldn't do both perfectly, so for lack of a better option, they chose to demote Pluto.
Any definition that would include Pluto and those many other objects wouldn't really have any benefit, other than simply including Pluto. It might not be the best reason ever, but for what is essentially a completely arbitrary decision, any reason is good enough.

[halfeye]

The thing is, planet is an arbitrary distinction. It always will be, no matter what they do. In this case, they chose an arbitrary distinction that was clearly defined, and almost entirely consistent with what had been done before. Unfortunately, they couldn't do both perfectly, so for lack of a better option, they chose to demote Pluto.
Any definition that would include Pluto and those many other objects wouldn't really have any benefit, other than simply including Pluto. It might not be the best reason ever, but for what is essentially a completely arbitrary decision, any reason is good enough.

Any reason is good enough?

The sky is blue so Pluto isn't a planet? The sky is green so Pluto isn't a planet? Today is Tuesday so Pluto isn't a planet? I don't agree that those would be at all close to good enough.

As I said above, I don't much care about whether Pluto is defined as a planet or not, though I think it's a shame they trashed so much history for the sake of pedantry, but the rule they made up to do it with is just silly. I totally understand the desire to have a metric that is independant of the particulars of the Earth and the Solar system, but while the metric they chose is independant of the Solar system, it totally fails to deal with potential other stellar systems in a reasonable way. At Pluto's orbit an Earth mass object would not be a planet by the metric chosen, and further out a Jupiter mass object would not be a planet by the same metric. We've probably already detected Jupiter mass minor planets by this silly definition.

[Peelee]

I think it's a shame they trashed so much history for the sake of pedantry

What history?

[Chronos]

Quoth Aedilred:

The confusion only comes because we've developed a separate culinary category for sweet fruit... not all of which are actually fruit, come to that (rhubarb)...

Or strawberries, or sweet potatoes, or hibiscus, none of which are botanically fruits, but all of which get used as fruits in some contexts.

halfeye, they had a choice between "throwing out" a small amount of history, or a large amount. "Historically" (meaning, less than a tenth of the time that people have been talking about planets), there's been a list of nine planets. But that didn't work, so they had the choice of going to a list of eight, or a list of hundreds. It'd have been a far greater sleight on "history" to expand the list so greatly.

[Tyndmyr]

Our moon is bigger than Pluto. As far as celestial bodies go, it's really small. Which is what "dwarf planet" means. Seems pretty appropriate to me.

It's been proposed frequently that the Earth/Moon system is basically a dual planet system. Sure, it's got a diameter only about a quarter of Earths, but the moon is unusually large in comparison to other planet/moon systems in the solar system, it's tidally locked to the Earth, affects our tides strongly, and would be a planet in its own right if earth suddenly vanished. The earth/moon gravitational center is only just within the earth anyways.

So, the idea of pluto being a planet is not so very ridiculous.

Any reasonable definition that includes Pluto is going to include a lot of planets - there's somewhere around 43 candidates, and that's just what we know of so far. This really isn't a political issue.

Well, exoplanets exist as well, so that ship has sort of sailed?

Only one asteroid, Eris, is larger than Pluto, so it is quite possible to make a definition that includes pluto still, but isn't crazy. At most, including both Eris and Ceres would give us 11 planets, and not have much risk of further changes.

The reason that Pluto was kicked out, not clearing its orbit, on account of Neptune crossing over it, would also obviously apply to Neptune, and nobody is defining Neptune as a dwarf planet. Thus, politics(at least of the astronomer sort). It's an arbitrary application of an arbitrary definition to arrive at a pre-concluded end, which some people are unhappy with. Other definitions, such as forming itself into a sphere thanks to gravity, seem a little less arbitrary, and generally do not attract as much dislike.

[hamishspence]

The reason that Pluto was kicked out, not clearing its orbit, on account of Neptune crossing over it, would also obviously apply to Neptune, and nobody is defining Neptune as a dwarf planet.

"Clear" in this case, means "clear enough". Jupiter shares its orbit with plenty of asteroids - the Trojans - but nothing close to Jupiter in size.


Similar principle would apply to Neptune and Pluto. Pluto is vastly smaller than Neptune, so it's reasonable to say that Neptune has cleared its orbit of objects of comparable size.

[Tyndmyr]

"Clear" in this case, means "clear enough". Jupiter shares its orbit with plenty of asteroids - the Trojans - but nothing close to Jupiter in size.


Similar principle would apply to Neptune and Pluto. Pluto is vastly smaller than Neptune, so it's reasonable to say that Neptune has cleared its orbit of objects of comparable size.

I suppose dual planetary systems are then defined out of existence, and the Earth ceases to be a planet on account of its moon. Unless, of course, we introduce a number of rules to specify the exact end result we want. The system of definition that this rests on is extraordinarily kludgy.

Plus, the entire concept of gravitational dominance is pretty dodgy, given orbital resonance.

You can say, as the IAU did, "oh, but we're not counting those objects which will never collide, thanks to orbits or resonance", but....then Pluto should be fine again, because it and Neptune won't collide thanks to resonance.

Basically, Pluto got defined away because a bunch of folks hated the idea of adding a tenth planet, because they had no system for adding additional planets, and got carried away with bureaucracy.

[hamishspence]

Basically, Pluto got defined away because a bunch of folks hated the idea of adding a tenth planet, because they had no system for adding additional planets, and got carried away with bureaucracy.

IMO it's no different from redefining Ceres down from planet to "biggest asteroid in the asteroid belt".

[Tyndmyr]

Ceres doesn't have the historical weight of Pluto, though. Pluto's been an accepted planet for quite some time. And in the search for other Pluto like objects, this has largely been framed as a search for a tenth planet.

It sort of smacks of changing the rules because you don't like the results.

Fortunately, the IAU doesn't have the power to do much of anything if you care to ignore them.

[Peelee]

It's been proposed frequently that the Earth/Moon system is basically a dual planet system. Sure, it's got a diameter only about a quarter of Earths, but the moon is unusually large in comparison to other planet/moon systems in the solar system, it's tidally locked to the Earth, affects our tides strongly, and would be a planet in its own right if earth suddenly vanished. The earth/moon gravitational center is only just within the earth anyways.

The Moon being tidally locked to Earth and the gravitational center being within the Earth both sound like good reasons for the Moon to not be a planet, though.

Ceres doesn't have the historical weight of Pluto, though. Pluto's been an accepted planet for quite some time.

There are living people who are older than Pluto's designation as a planet. Dinosaurs were discovered more than a hundred years before Pluto, and yet when scientists said "hey apparently they had feathers" it had less pushback than "we're not calling Pluto a planet anymore." You can talk about "historical weight" all you want, but in reality there's barely any historical weight behind it. That argument is basically little more than "it was a planet all my life" in fancier clothes. And that's ignoring how "it used to be that way" is an inherently poor argument to begin with.

[Strigon]

Any reason is good enough?

The sky is blue so Pluto isn't a planet? The sky is green so Pluto isn't a planet? Today is Tuesday so Pluto isn't a planet? I don't agree that those would be at all close to good enough.

You know, it's considered very poor form in debates to deliberately take the most ridiculous interpretation of an argument, and mock it.
None of those are reasons. Not to any practical definition of the term.

As I said above, I don't much care about whether Pluto is defined as a planet or not, though I think it's a shame they trashed so much history for the sake of pedantry, but the rule they made up to do it with is just silly. I totally understand the desire to have a metric that is independant of the particulars of the Earth and the Solar system, but while the metric they chose is independant of the Solar system, it totally fails to deal with potential other stellar systems in a reasonable way. At Pluto's orbit an Earth mass object would not be a planet by the metric chosen, and further out a Jupiter mass object would not be a planet by the same metric. We've probably already detected Jupiter mass minor planets by this silly definition.

This is correct.
A planet is defined as much by its role as by its physical characteristics. This is a very helpful definition, astronomically speaking, because it helps to show how objects interact, and what the dominant forces/bodies are in a given region of space.
Earlier I made the comparison between planets and apex predators; the lion is an apex predator, as it is not preyed upon by any animals. If it were introduced to an animal that preyed upon it, either by relocation or the presence of a new predator in its habitat, the lion would cease to be an apex predator. By this very same argument, the idea of having apex predators is "silly."

[Magic_Hat]

What kind of science blasphemy is this? I heard that Pluto isn't a planet but a dwarf planet. That like saying Tomatoes isn't even a vegetable but fruits. Please, someone give me an honest answer to this Pluto debate.

Wait, are you just learning this? This was news back in like 2007.

[hamishspence]

The Moon being tidally locked to Earth and the gravitational center being within the Earth both sound like good reasons for the Moon to not be a planet, though.

Indeed. Especially considering the Earth itself is not tidally locked to the Moon.

The same applies to most satellites - except the Pluto-Charon system - that's the only one where the primary is locked to the secondary and vice versa.