Can We Call Pluto and Charon a 'Binary Planet' Yet? 115
astroengine writes The debate as to whether Pluto is a planet or a dwarf planet rumbles on, but in a new animation of the small world, one can't help but imagine another definition for Pluto. As NASA's New Horizons spacecraft continues its epic journey into the outer solar system, its Kuiper Belt target is becoming brighter and more defined. Seen through the mission's Long Range Reconnaissance Imager (LORRI) camera, this new set of observations clearly shows Pluto and its biggest moon Charon locked in a tight orbital dance separated by only 11,200 miles. (Compared with the Earth-moon orbital separation of around 240,000 miles, you can see how compact the Pluto-Charon system really is.) Both bodies are shown to be orbiting a common point — the "barycenter" is located well above Pluto's surface prompting a new debate on whether or not Pluto and Charon should be redefined as a "binary planet".
Admit it. (Score:4, Funny)
You're just trying to troll Neil Tyson for the hilarity that ensues.
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And xkcd, and a Psych movie if there ever is one. (You can't entirely hate a TV show where "You heard about Pluto?" is used as a pick-up line.)
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Obligatory JC (Score:2)
That's why it stings,
They don't think that you matter,
Because you don't have pretty rings."
-Jonathan Coulton
Pluto's a dog. what's Goofy? (Score:5, Informative)
Re:Pluto's a dog. what's Goofy? (Score:4, Insightful)
July 2015 (Score:2)
Well, Earth has an unmanned expeditionary mission that will take pictures of Charon in July 2015 =^-^=
Outrageous discrimination! (Score:5, Funny)
What's with this "dwarf" nonsense — and big planetarism [slashdot.org]? We demand equal gravity for all planets [thepeoplescube.com]!
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How dare anyone make fun of Pluto after all it's been through! [quickmeme.com]
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What's with this "dwarf" nonsense â" and big planetarism? We demand equal gravity for all planets!
Why? We don't grant equal gravity to all arguments. Discrimination! :)
I think we should grant equal comedy to all arguments. They everybody would "lighten up" and have a good time.
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And we should also grant equal comedy to all planets. Even before Charon was named I voted for "Goofy".
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But we need more trickle-down gravity until the sun bursts forth and spreads the wealth to the poor Kuiper ghettos, as the job creating nova the sun could be if not for the strangulating socialist regulation of the speed of light stuck at c.
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pedant point: Javascript isn't a programming language, the clue is in the name: it's a SCRIPTING language.
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Diameter, in km
Mercury ... 4,880 ..... 12,104 ..... 12,756 ...... 6,794 ... 142,984 ... 120,536 ... 51,118 ... 49,532 ....... 2,222
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto
Pluto's diameter is half the diameter of Mercury. Should we also consider Mercury a dwarf planet? Can the Earth be considered to be in the same league as Jupiter/Saturn as they have 10 times the diameter of Earth?
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They are not considered to be in the same league. The classes are: Gas giants, terrestrial planets, dwarf planets.
Re:Self-awareness (Score:5, Insightful)
Interestingly, Jupiter is the only planet which has it's barycenter with the sun outside of the sun.
The definition of whether something orbits something else, or whether it is a binary system is pretty arbitrary. It would be nice and neat if we could say that if the barycenter is inside the larger body, the smaller body is orbiting the larger, but that would mean that Jupiter would not be orbiting the sun.
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why yes, you can have a quarter of a penny, since that's all I have.
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The moon is currently 239,000 miles away, and the barycenter is at 0.75 Earth radii from Earth's center. If the barycenter was at the earth's surface, how close would the moon be?
For the purpose of this calculation assume the earth is a uniform sphere with a mass of 5.97x10^24 kg and a diameter of the earth is 7,900 miles, and the moon is a uniform sphere with a mass of 0.0123 earths and a diameter of 2,160 miles.
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320,000 miles
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BTW, I actually did the full calculations and accounted for the radius of earth/moon in the distance. But according to the equation for calculating barycentric coordinates [wikipedia.org], the distance of the barycenter from the center of the primary is linearly proportional to the distance of the centers of mass of the two bodies... so a pretty close estimate would have been (1 / 0.75) * 239,000 miles.
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a couple Qs if you don't mind, because you obv know a lot about this. so I guess if the barycenter is not in the middle of earth, then the earth wobbles as the moon goes around. Is this what causes tides, it's essentially the sloshing of the ocean as the earth wobbles? I always knew that "the moon causes tides", but I never understood
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a couple Qs if you don't mind, because you obv know a lot about this.
I'm just a guy who was interested enough to Google and throw together some calculations.
so I guess if the barycenter is not in the middle of earth, then the earth wobbles as the moon goes around. Is this what causes tides, it's essentially the sloshing of the ocean as the earth wobbles? I always knew that "the moon causes tides", but I never understood the mechanism.
The gravitational forces between the earth and moon are major components of tides. However the barycenter doesn't seem to contribute directly. Moving the earth and moon farther apart (and thus moving the barycenter further away from the center of the earth) actually causes the tides to become weaker. This actually happens regularly as the moon gets closer and then farther from the earth in its orbit (the moon's orbit
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In retrospect I don't like how I phrased this:
Thus, all we need to do is figure out at what new distance R2 the new orbital velocity V2 = V * (1 / square root of 2).
Change it to the following:
Thus, all we need to do is figure out at what new distance R2 the original orbital velocity V = V2 * (square root of 2), where V2 is the velocity of a circular orbit at distance R2.
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if the barycenter is not in the middle of earth, then the earth wobbles as the moon goes around.
The barycenter for any two objects is never the middle of either. It's always somewhere on a line directly between the two centres of mass. Every individual satellite that humanity has launched makes the earth wobble a little bit (albeit a miniscule amount).
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Defining it based on barycenter will lead to curious outcomes. What if the barycenter moves into and out from the planet (such as with multiple moons)?
And what if Pluto had a second moon, equal in mass and distance as Charon but always on the exact opposite side (L3)? The barycenter would be at the center of Pluto, but why does this change cause Pluto to become a "real" planet?
Questions like this really reveal the definitions. (Score:2)
The answer is simple - that Lagrange point is not stable, so the moon would not remain there. Each moon would be pulled from that point by the other's gravity, until they either collide or one or both items are thrown from their orbits.
So as a planet cannot have two moons that orbit opposite each other, the concept of a binary planet with a definition based on the location of its barycenter is valid. But we'd first want to see one - Pluto/Charon is a poor example, as Pluto is considerably larger and heavier
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Agreed, that one is a bit far fetched. It's a many-body problem and all it takes is a bit of eccentricity or pull from other moons, planets, and the sun to destabilize.
But back to the first question, what if the barycenter moves in and out of the planet due to multiple moons? This would be akin to the solar system [youtube.com], where the barycenter moves in and out of the sun. I don't know if we could easily call it a ternary planet, quaternary planet, etc.
I think I prefer Isaac Asimov's tug-of-war definition [wikipedia.org] of a bi
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Another reason I don't care for the barycentric approach is because it depends so highly on the radius of the larger body. What if the barycenter of the moon were right above the surface but well within the atmosphere? What about a gas giant where the definition of the radius is a bit fuzzier?
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Barycenter not closer to either planet than a chosen percentage of the distance between their centers would be better.
Re: Questions like this really reveal the definiti (Score:2)
That definition would reduce the problem to the relationship of their masses.
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I was thinking of this thread again (the tug-of-war definition) and thought of another interesting thing to calculate: What if I swap Pluto and Charon in the equation? Would it indicate that Pluto is also more influenced by Charon than the sun at times?
The answer is yes, meaning Pluto does not have a concave orbit either. The tug-of-war value focusing on Pluto as the primary body is 337.3 at perihelion, but focusing on Charon as the primary body it is 39.3. Since both are greater than 1, this means Plut
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Again, I would have to be convinced that a group containing more than two objects with sizes within an order of magnitude of each other would be stable. Myself, I can't see it. Two large moons would push each other into chaotic orbits which would, sooner rather than later, lead to either a collision or an ejection.
The only way I can see a system with two large moons is with a planet that is completely dominant, such as Saturn or Jupiter and it's moons. (I'd argue, for instance, that Earth could not have hel
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The Earth-Moon barycenter is very nearly outside of Earth itself (it's about 0.75 Earth radii from Earth's center), so let's not get too high on our horses...
And the Earth - Moon should be classified as a binary planet. They are in such an intimate dancing orbit with each other that neither one can be adequately described without refering to the other.
This is more than a semantic squabble. Any exoplanet that is likely to support life as we know it must not only be in the Goldilocks zone, it must also have a companion close enough to create tides (and tide pools, and generally act as a celestial stirring rod).
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That's no moon! (Ask David Weber)
Binary yes, planet no. (Score:5, Insightful)
Re:Binary yes, planet no. (Score:4, Insightful)
Anything that is a sphere and orbits a star is a planet. Asteroids don't have sphere shape. Same goes for comets. The reason for the name "dwarf planets" is that of naming issue. There are more than 100 planet object out there, most of them smaller than planet Mercury.
Haumea is a planet, but is minor elongated due it's rapid orbital period.
http://en.wikipedia.org/wiki/H... [wikipedia.org]
List of other dwarf planets.
http://solarsystem.nasa.gov/pl... [nasa.gov]
Then there is a chance of Earth size planets (both above and below in size and mass) in the outer region of our solar system that have not yet been discovered. At least there are clues about them today, even if they have so far not yet been found. It is my guess they are going to be found, given time and advances in technology that allows for better detection of outer orbital planets in our solar system.
http://www.space.com/7728-eart... [space.com]
http://www.theguardian.com/sci... [theguardian.com]
There is a lot out there that we don't have no clue about and there are discoveries to be made (if the funding holds).
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Anything that is a sphere and orbits a star is a planet. Asteroids don't have sphere shape. Same goes for comets.
Ceres and Vesta are nearly spherical, yet are asteroids. Do they get counted as planets too? (They used to be.)
You're right that the definition was tailored to keep the number of defined "planets" within reason. There was no way to include Pluto in this category and NOT include Eris, Haumea, Makemake, etc., so the definition was tailored to exclude them. It also happens to exclude Ceres and Vesta, though it wouldn't be a huge problem if they were considered planets (as they are the only two members of their
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Ceres is a dwarf planet. Same reasons as Pluto.
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neither has Jupiter. Zing.
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neither has Jupiter. Zing.
"Cleared its orbit" means, the planet controls everything which shares or crosses orbit with it. This may mean the usual moons, but also oribtal resonance (such as the Pluto-Neptune resonance) and minor bodies oribiting the Lagrange points of the planet (Trojans at L4/L5) instead of the planet itself like the usual moons.
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I think the IAU new definition of a planet includes the condition that it has cleared its orbital track of any other significant debris. Pluto hasn't, it has at least seven satellites and there are many other unconnected bodies sharing the same orbit (last I heard at least twelve, of significant size, at various and seemingly random angular separations)... ironically, this would disqualify Jupiter as well, since it is preceded and followed in its orbit by two clouds of debris (Trojan asteroids) which are lo
Pluto is a Planet (Score:1, Insightful)
Pluto is a planet. The definition of a planet is arbitrary, and always will be.
Trying to forcefully change the definition after it's already in use is fucking retarded and does nothing but cause confusion.
For other instances of dipshits trying to hijack language and make it worse, see "non-flammable" and the dipshits who insist that a kilobyte is 1000 bytes.
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"Inflammable" means shit is capable of bursting into flames.
"Non-inflammable" means it isn't (easily).
"Nonflammable" was created by an asshat who wanted to remove confusion (which didn't exist).
"Flammable" was then created to be the opposite of the new fake opposite.
"Inflammable" is derived from the Latin inflammare, which means able to be set on fire. This is the correct usage.
"Nonflammable" is derived from "non" + "flammare", meaning to set on fire, + "able". This is completely fucking incorrect usage.
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why? as you just explained, it means "not able to be set on fire"; more literally it might mean "not able to be a fire". either way it's perfectly fucking clear, and it's easier to say. you're an idiot.
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Pluto is a planet. The definition of a planet is arbitrary, and always will be.
What makes your arbitrary definition of "planet" - one that allows you to declare without qualification that it is a planet - better than the IAU's?
Trying to forcefully change the definition after it's already in use is fucking retarded and does nothing but cause confusion.
Not when the old definition is itself revealed to be "fucking retarded" (technical term, is that?) and causes more confusion once more data becomes available.
see "non-flammable"
Did you mean "inflammable"?
and the dipshits who insist that a kilobyte is 1000 bytes.
What, like the dipshits at the the International Organization for Standardization? Just because you don't like it, doesn't make everyone else unquestionably wrong.
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I'm totally baffled about the "non-flammable" thing. I think sex_conker just likes being confused because the alternative is too difficult for him.
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Pluto is a planet. The definition of a planet is arbitrary, and always will be.
What makes your arbitrary definition of "planet" - one that allows you to declare without qualification that it is a planet - better than the IAU's?
Trying to forcefully change the definition after it's already in use is fucking retarded and does nothing but cause confusion.
Not when the old definition is itself revealed to be "fucking retarded" (technical term, is that?) and causes more confusion once more data becomes available.
see "non-flammable"
Did you mean "inflammable"?
and the dipshits who insist that a kilobyte is 1000 bytes.
What, like the dipshits at the the International Organization for Standardization? Just because you don't like it, doesn't make everyone else unquestionably wrong.
My definition makes more sense and is better because it's ALREADY IN USE.
You can't fucking change the meaning of a word willy-nilly, because that causes ambiguity. Does the speaker/author mean the new definition or the old one? When was this written? What was the more popular definition at the time?
For inflammable, look up the fucking Latin roots inflammare and flamma.
For kilobytes, again, the issue is about what was in use already and how changing shit adds ambiguity. Computer science has damn good rea
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My definition makes more sense and is better because it's ALREADY IN USE.
You mean the "blah blah blah and Pluto" definition? Because that was pretty much the definition for some time...
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My definition makes more sense and is better because it's ALREADY IN USE.
A definition is not automatically better simply because it's already in use (indoor voice, please). It certainly doesn't intrinsically make "more sense" because of that fact.
In medieval times units of measurement were "defined" by lining up random churchgoers and measuring the combined length of their feet. Would you have resisted the introduction of a standardised measure [wikipedia.org] because the former was "already in use"?
You can't change the meaning of a word willy-nilly, because that causes ambiguity.
You're talking about the common usage of words. The IAU's problem was that their formal definiti
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If you want to call Pluto a planet, you'll have to call Eris, Haumea, Makemake, Ceres, and a whole bunch of others planets too.
Keep in mind that Ceres is spherical, orbits a star, and was known for 200 years but was NOT considered a planet during this time.
Language can be arbitrary, sure. But why insist on it being self-contradictory?
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And I would consider them planets.
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They are dwarf planets. Not good enough for you? Do you have to lump every single non-asteroid object in the solar system in the same category?
The purpose of language is to communicate ideas in an efficient way. There's a reason, for instance, that the most commonly-used words are the shortest ones, and that things that are semantically different are given different words.
When using the word 'planet', it is far more likely that you have the 8 actual planets in mind, not Makemake or Haumea. So it makes sense
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PS, I want to add that the IAU doesn't care what the average Joe calls them. Their definitions are for their own internal scientific usage. You can call them whatever you want. But if you want the proper term that actual astronomers use, it's "dwarf planet."
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> Pluto is a planet. The definition of a planet is arbitrary, and always will be.
If you can find an astronomy textbook from the 1830's or early 1840's, it'll list 11 planets...
Mercury
Venus
Earth
Mars
Ceres (discovered 1801)
Pallas (discovered 1802)
Juno (discovered 1804)
Vesta (discovered 1807)
Jupiter
Saturn
Uranus (discovered 1781)
As time went on, more and more asteroids were discovered. Today, there are a few hundred thousand asteroids. To keep the number of planets at a manageable number, the asteroids wwere
What debate? (Score:5, Informative)
How can you "debate" about that?
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I know! It's the best kind of debate: having no substantial meaning at all, it can last forever as an excuse for people to insult and trump one another. It's a perfect Slashdot article; we need more of these.
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Planet and Dwarf Planet are arbitrary labels defined by the IAU.
How can you "debate" about that?
Well, they're not really arbitrary. There are at least three points you can argue about:
1. Argue to change the definition (actual written words), which determines which is which and what isn't either.
2. Argue about interpretation of the defintion. Though, if this succeeds, then it makes the definition ambiguous, and the classification of border cases does become arbitrary.
3. Argue about the chosen terms "planet" and "dwarf planet". For example I'm personally not too happy having "dwarf planets" which are no
This is pretty damn silly (Score:4, Interesting)
This mission will put a new spotlight on Pluto and its âoedwarf planetâ status, potentially highlighting its current classification as a woefully inadequate description of such a dynamic and interesting binary system.
Ok, so it's a "binary dwarf planet" - can we tone down the prose now?
So the Sun/Jupiter system as well? (Score:2)
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No, because Jupiter is not a star. It is the same reason that Pluto/Charon is not a binary planet as neither of them is a planet.
Still askew (Score:1)
Unless Pluto (and Charon) shifted orbit into the planetary plane, nothing has changed and any desire to call it a planet is just sentimentality.
pluto doesn't care (Score:2)
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it's all fun and games until someone blows up a planet.
miles? (Score:1)
No we can't (Score:2)
No phone lines yet. Sorry.
Betteridge says (Score:2)
No.
Self determination (Score:2)
I suppor tthe right of the people of Pluto to decide their own destiny, and not be ruled by any arbitrary group of people on some other planet.
Freedom for the Plutocrats
AHEM... (Score:2)
OOOps! (Score:4, Informative)
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Among the moons of Pluto are... wait, I'll come in again.
This is old news (Score:2)
We've known for at least a decade now that Pluto/Charon's barycenter is outside the mass of Pluto. That was one of many arguments used to delist Pluto from the Solar System planets. Those same "Pluto is a planet" fossils probably would demand Ceres be restored to planetary status, if they lived two hundred years ago.
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Earth/Luna is a binary planet by the criteria.
It's not. The center of gravity [infoplease.com] is under Earth's surface.
Most significantly, Luna's orbit is never convex with respect to the Sun.
The Moon's orbit is convex [nus.edu.sg].