Amid new push to make Pluto a planet again... Get over it, ice-world's assassin tells El Reg The ongoing argument over whether Pluto is an actual planet or just a dwarf on the outskirts of the Solar System has heated up again – with a new proposal to reapply planetary status to the distant iceball. In a vote in 2006, the International Astronomical Union (IAU) decided to reduce the status of Pluto to that of a dwarf …
Yeah that's kind of an obvious problem, and when you get there it's mostly just sighing, facepalming, and but Tradition!, which is kind of the whole Pluto=planet argument anyway.
But you have to be careful with the "sun orbit" requirement anyway, since pendants like myself will point out that the Jupiter-Sol barycenter is outside the sun, so technically they orbit each other.
So how do you deal with the Pluto - Charon system?
Charon is spherical, and has half the diameter of Pluto (and about 1/8 the mass), making Pluto - Charon a binary system (much more so than Earth - Moon, for example). And the barycentre of Pluto - Charon lies WELL outside Pluto.
Or isn't the Earth a body that orbits the Moon? Just like two masses of whatever size have equal gravitational attraction, so two bodies in close proximity equally orbit each other. Because we earthlings have a geocentric viewpoint, we like to think the moon orbits the Earth but in fact they orbit each other and the Sun in a spiral corkscrew pattern. Likewise the planets orbit the Sun and together the bodies in the solar system orbit the Milky way in a corkscrew fashion.
So, why shouldn't the Moon be classified as a co-planet!
@smartermind - Isaac Asimov, bless his memory, pointed out many years ago that there's something odd about the Earth-Moon system, and that is that the Sun exerts a greater pull on the Moon than the Earth does - a situation which, if memory serves me correctly, exists for no other moon in the solar system.
Also, if you look at a projection of the Moon's motion from a heliocentric view, the moon and the Earth both orbit the Sun in intertwined orbits, and the Moon's orbit about the Sun is always concave.
Given all that, despite the fact that the barycentre of the Earth-Moon system is just about within the Earth's surface, one could make a strong case for arguing that the Moon isn't a moon at all but the other part of a binary planet system along with the Earth.
Alternatively, given the current ruling for what constintutes a planet, as the Earth clearly hasn't cleared its orbit of other sizable bodies (because of the Moon, which isn't actually a moon, one could argue as per the above), then the Earth isn't a planet, unless one counts a binary planet as a planet. (Which then fuels arguments about Pluto/Charon)
And no, I don't think the Earth is not a planet, personally. It's just a MUCH harder thing to define than most people think, when you consider all the varied edge cases that can potentially exist.
And frankly - the universe doesn;t care what we label things. They're out there, they're interesting, they're worthy of investigation, whatever the heck you call them :-}
"Or isn't the Earth a body that orbits the Moon? Just like two masses of whatever size have equal gravitational attraction, so two bodies in close proximity equally orbit each other." --- smartermind
They're rotating around their 'barycentre' or mutual centre of mass. However for Earth/Moon that point is below the surface of the Earth and for Pluto/Charon that point is well outside Pluto.
With a little thought, the definition could be updated in such a way that allows Pluto to be defined as a planet, but excludes the Moon (and those of other planets).
If we take the proposed definition quoted in the article as a starting point:
"A planet is a sub-stellar mass body that has never undergone nuclear fusion and that has sufficient self-gravitation to assume a spheroidal shape adequately described by a triaxial ellipsoid regardless of its orbital parameters."
The article notes two requirements from the 2006 definition which are the cause of all Pluto's problems:
* Clearance of all other objects in the same orbit
* Orbits the Sun
The first of these is clearly imperfect because small objects can still exist on the same orbit as larger objects having not been cleared - even larger ones if they're sufficiently distant in that orbit, as this highly scientific documentary makes clear.
Orbiting the Sun is also a problem because it doesn't allow for rogue planets, as noted in the article - and although we think of it as the moon, that time it went rogue (as detailed in this documentary) it should arguably have been considered a planet.
So the definition could perhaps scope out whether or not it is orbiting a larger body, and if so the nature of that body. If it is orbiting a larger body that has never undergone nuclear fusion, it is a moon - otherwise it is a planet.
That makes Pluto the planet, and Charon a moon - and because it doesn't specify that it must be orbiting a larger body, rogue planets can be planets too. If you want to take the barycentre into account, then it is the larger body of those that share a barycentre.
'The Moon' IS a planet not 'A Moon'.
If the Earth was to vanish it's orbit would continue pretty much unchanged.
https://io9.gizmodo.com/is-the-moon-a-planet-1064356920
Also, It's long past bloody time that El Reg made it easy to include hyperlinks, or at least made the information on how to embed them clear, complete and easy to find.
I think I found a reference once, but it assumed html expertise. Is a button that hard to implement?
"Also, It's long past bloody time that El Reg made it easy to include hyperlinks, or at least made the information on how to embed them clear, complete and easy to find."
From about halfway down the El Reg Forums FAQ:
"You need to put in the code yourself. You are a techie. This is not hard."
Troll icon, because I've just done the thing you've asked for help with, without explaining how I did it. But I don't know how to show an example of how you insert a hyperlink, without it appearing as a hyperlink!
Thanks for your post with a link in it Red Bren. I used view-source and had a practice on an old forum post
I tested with - <_a _ _h_r_e_f_=_"_h_t_t_p_s_:_/_/_c_9_._i_o_/_"_>_C_l_o_u_d_ _9_<_/_a_>
take out the '_' characters
I thought that there was some substitution of '[' and ']' for '<' and '>' but that may have been some other forum.
Thank you for that link. I learned that I had totally belonged to the group that imagined that the Moon orbited Earth, but it actually orbits the Sun with a bit of gravitational perturbation from that ol' ball of Earth.
A disturbing perspective. I might, with the good help of my friend Jack, be able to drink that away and consider that lizard men are once again trying to conspiracy-theory influence reality, but that will take some time.
In any case, I cannot shake the belief that the discussion around the planetary status of Pluto is more down to the fact that it is the only planetary body discovered by an American than any truly scientific discussion. Typical New World nuisances that have to have something important to their name since they only have a quarter of a millennium to show History.
Personally, I find it much more logical to imagine that Pluto belongs to the undoubtedly large Kuiper Belt Objects group rather than consider it a Planet. Maybe adding another rule, something along the lines of "a planet cannot have a moon larger than one-half its mass" would quell the discussion (yeah, right).
All of this will not keep Planet X from being called a Planet, though, as soon as we find where the bloomin' dale it is.
Pluto is both a small planet and a Kuiper Belt Object. The two are not mutually exclusive. The first tells us what it is; the second tells us where it is. While the Kuiper Belt is composed largely of tiny, shapeless rocks and balls of ice, it does host some small planets too.
"But you have to be careful with the "sun orbit" requirement anyway, since pendants like myself will point out that the Jupiter-Sol barycenter is outside the sun, so technically they orbit each other."
I thought one of the reasons for Pluto's demotion was due to its barycenter with Charon being beyond its radius.
On a further point of pedantry, the fact that the Jupiter-Sol barycenter is outside the sun is why the sun is not classed as a planet...
It is a pity that we have no name for a body that is in such a relationship. It was always the weakest point about the orbit-clearing business. Neptune has cleared its orbit. That Pluto survives is because it is in an orbital resonance and therefore is never in Neptune's path.
Wikipedia informs me that Laplace was the first person to analyse such systems so perhaps we could call Pluto a Laplacian moon of Neptune. Astonomers who care about orbital relationships can hang on the word "Laplacian". Planetary scientists who care about geology can hang on the word "moon".
I've just had a 9-planet Orrery with orbiting moons made by a UK engineer ... which of course includes Pluto. Should Prof. Michael Brown ever drop in for tea I can easily detach the Pluto arm to avoid ruffling his feathers. Joking aside, I foresaw the possibility of the reinstatement of planetary status to Pluto so decided that including it in the Orrery was justified.
Google "Genesis Orrery Staines & Son" to see the beast
Because that's what this "argument" puts me in mind of: a bunch of evangelists arguing about something that really just does not matter.
Like many Reg readers I'm keen on science, and as such I would have thought there were at least 1,000 things about The Body Known As Pluto which are worth finding out, not a single one of which depends upon whether some accidentally evolved crania full of blue mush six billion miles can't agree whether to label it as a planet, dwarf planet or scubble-wang-doo.
"A difference that makes no difference is no difference"
So as I understand it what you're proposing is a solution where all can save face. So yes, Pluto is a planet. Except we're changing the word planet to "scubble-wang-doo".
Thus the next question, does that mean Pluto remains as a planet, along with perhaps Ceres and the like - leaving us with 8 scubble-wang-doos in the solar system? Or is Pluto also now a scubble-wang-doo as wee?
If the hypothetical planet that messes up Kuiper object orbits gets actually discovered, it will almost certainly be
1. a gas/ice giant, and
2. a dwarf planet under the current definition (because of not "having cleared its orbit")
Then the whole system will probably collapse under the silliness of having a dwarf giant planet.
By the way, the Moon is not a moon, it's one half of a binary planet. Not sure which idiot called it Moon but it should obviously be renamed. I propose to call it the planet Minerva going forward.
@imanidiot, the IAU seems to disagree with you:
https://www.iau.org/public/themes/naming/
"So the IAU does recognize official names for the major planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune) and Earth's satellite (Moon)."
Note that it is called "Moon", not "the Moon".
Calling it Luna makes you sound like somebody who read too much Heinlein.
And no, "Tellus" is not the official name of Earth.
Or like lots of things, they could have a list of "traditional" solar system planets or whatever they want to call them, which could differ from strict (in this case planet) definitions.
In the UK we have something similar for counties, "administrative" counties are defined based on administrative region boundaries, but there are things called "ceremonial (or geographic) counties" (that simplistically relate to geographic regions back in the day) and may encompass parts of multiple "administrative" counties or even just part of an existing county.
Some "ceremonial county" equivalent for list of traditional solar system planets solves the problem for everyone, you can have "proper" definitions excluding Pluto, but the "ceremonial" planet list could include it
"I presume it's a Very early sandwich?"
A Very Early Morning Jam Sandwich.
"My nine year old has a mnemonic which works for him and which does not include Pluto. More importantly he totally gets why Pluto does not qualify."
Well he has time to work out why Pluto should also qualify as a planet.
This is not the case. Many teachers continue to teach the controversy, present both sides, and let kids decide for themselves which view they support. Do not just assume every teacher and every textbook blindly followed a controversial decision by four percent of the IAU. I am proud to be one of many amateur astronomers who regularly reaches out to teachers encouraging them to teach the debate rather than just present the IAU view as gospel truth.
A definition that feels the need to say "regardless of..." anything is not a good enough definition. It's just another argument.
The definition should clearly say what something is; not define it by saying "well, it's not one of those, or one of those, or that thing over there".
It's too late for that now. If science hadn't labelled Pluto as a planet for 70 years, there'd be no problem. But they did, so now they're stuck with it. And people will keep being annoyed that they've changed it.
The solution is either to change it back, and admit that there isn't a particularly satisfactory "perfect" definition of a planet - or to put up with loads of people complaining until the generations who learnt it was a planet die.
It's a bit like being told that a banana is a berry. That's all very interesting, but nobody but a biologist needs to care. Similarly I believe a coconut isn't a nut.
Or, as the saying goes, knowledge is knowing that a tomato is a fruit - wisdom is not putting one in a fruit salad.
Although saying that, my Nan used to make delicious tomato jam.
No, this is a straw man argument and is blatantly false. Support for Pluto's planet status is based on preference for a geophysical rather than dynamical planet definition--in other words, one that is based first and foremost on an object's intrinsic properties rather than on its location.
Brown never "killed" Pluto, and his obsession with the idea that he did is completely unprofessional and unscientific. It is nothing more than a means of branding himself to sell books and gain money and fame. Kirby Runyon's planet definition makes a lot more sense than that of the IAU because it is focused on an object's intrinsic properties rather than on its location. There is no need for kids to worry about memorizing 100 planets because memorization is not important for learning. It is an archaic means of teaching from a time when we knew little more about the planets other than their names. Instead, kids and adults should be taught the different subclasses of planets and their definiting characteristics. We don't ask kids to memorize all the elements of the Periodic Table or all the rivers and mountains on Earth, and similarly, we don't have to ask them to memorize a list of planet names.
Brown is out and out wrong when he says that worlds like Pluto have more in common with tiny, shapeless asteroids, comets, and KBOs than with the larger planets. Pluto and the other dwarf planets have all the features the larger planets do. They have geology and weather and are layered into core, mantle, and crust. The only difference is the dwarf planets are smaller. The Dawn and New Horizons mission clearly revealed many active planetary processes on Ceres and Pluto, both of which may have subsurface oceans that could host microbial life.
Brown is also wrong in saying that just a small but vocal group rejects the IAU defintion and has been advocating for a geophysical one. This is blatantly untrue. While some people are more vocal than others, there is a huge cohort of planetary scientists, amateur astronomers, educators, writers, and informed members of the public who never stopped considering Pluto a planet and oppose the IAU claim that dwarf planets are not planets at all. We have actively promoted a better definition including dwarf planets as planets for over 10 years and will continue to do so.
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