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Is Pluto a Binary Planet?
astroengine writes "If the Pluto-Charon system were viewed in a similar way to binary stars and binary asteroids, Pluto would become a Pluto-Charon binary planet. After all, Charon is 12% the mass of Pluto, causing the duo to orbit a barycenter that is located above Pluto's surface. Sadly, in the IAU's haste to define what a planet is in 2006, they missed a golden opportunity to define the planetary binary. Interestingly, if Pluto was a binary planet, last week's discovery of a fifth Plutonian moon would have in fact been the binary's fourth moon to be discovered by Hubble — under the binary definition, Charon wouldn't be classified as a moon at all."
The IAU has been trying to redefine things in bulk, and then growing discontent with those definitions and changing them yet again. It's a far cry from the organization's original role: Cataloging astronomical objects. To put it in perspective, they're like a librarian that changes the layout of the indexing system weekly. They don't actually move the books around, but they rename the aisles, recategorize things, and generally make a massive mess of it all.
But then, I'd expect nothing less from a committee of pseudo-scientists; They're so engrossed with their own administrations they've become cut off from the people they're supposed to be helping.
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As closely as they orbit each other, I'd say Pluto-Charon would be almost the example of such a system. Heck, it's almost a Rocheworld. :p
The barycenter of the Sun/Jupiter system lies at 1.07 solar radii from the Sun's core (i.e. outside the Sun). Is the Sun a binary star?
For those curious, the barycenter of the Earth/Moon system is well inside the Earth, despite the Moon relatively energetic orbit.
Do what thou wilt shall be the whole of the Law
The Death Star was so massive that when it orbited a planet it became a binary system.
I eat only the real part of complex carbohydrates.
Haven't you heard? Pluto isn't a planet at all anymore.
The issue with using the barycentre, is by moving two objects further apart without changing the mass, eventually the barycentre will be above their surfaces. The Jupiter-Sun barycentre is above the surface of the sun, but wouldn't be if Jupiter were closer. The Earth-Moon barycentre is about 75% of the radius of the Earth, but if the distance between them increased by about 25%, then the Earth-Moon barycentre would be above Earth's surface. So it is quite possible to have two bodies that are very influential on each other, but with the barycentre below the surface due to being too close. And the status could change simply by having one body move further away, like Earth's moon is currently doing.
8 regular planets, plus the Pluto-Charon binary which adds 10 more.
I do not understand at all the rage over Pluto's demotion from planetary status. Is it tradition? 'Traditionally' the Sun was thought to revolve around the Earth. Is it because children have to be sat down and gently told the truth, like about Santa Claus? Is it something more personal between individuals in astronomy? It's called *science* folks, and it's self-correcting. I just don't get why people are so upset.
My proposed definition: A binary system comprises two objects whose common center of gravity is above the surface of either object and the components of the system are similar in size and/or mass. This would Pluto-Charon a binary system and the Sun-Jupiter not a binary system.
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01010000011011000111010101 11010001101111001 000000110100 1011100110010000 0011000100110100101101110011 000010111001001111 00100101110
It claims the moon has 0.01% of the mass of Earth. In reality, it's closer to 1.2%.
There are two independent questions:
1) binary vs non-binary
2) dwarf planet vs planet
No need to bring up (2) in a discussion about (1).
only for the small minded.
Can I be the first to vote "who cares"? It's just a definition, its not like our understanding of Newtonian gravity rests on correctly assigning things into arbitrary categories. And can we please now get back to important things like arguing about whether C is a low level language?
The problem is not that it's too small. It's large enough to be a spheroid, so it's large enough to be a planet. If it existed in an orbit that was free of other large objects (e.g. Neptune and Kuiper belt objects), it would be a planet.
What a fool believes, he sees, no wise man has the power to reason away.
Because Pluto is not a planet.
Binary dwarf planets, sure. That seems a reasonable argument. But even treating Pluto and Charon as a single entity can't upgrade them to planet status.
It amazes me how this ~10 year old thread topic won't die even though it is lame as hell.
Except that, as of now, the *definition* of a planet involves "an orbit [...] free of other large objects". So that's like saying "the Moon would qualify as a planet if it orbited the Sun instead of the Earth", or more succinctly, "Pluto would be a planet if it weren't for the things that make it not a planet".
The problem is not that it's too small. It's large enough to be a spheroid, so it's large enough to be a planet. If it existed in an orbit that was free of other large objects (e.g. Neptune and Kuiper belt objects), it would be a planet.
So according to your definition Titan would be a planet, were it not for that pesky Saturn just over Titan's horizon.
Charon must have less density than water. How else could it repeatedly sail across the river?
The (IAU) definition also includes "is in orbit around the Sun,"
That means that there is no such thing as a planet outside the solar system.
...it's half a binary planet.
It's not *my* definition. It's *the* definition. Yes, Titan would be a planet if it were in its own orbit, as would most of the solar system's largest moons.
What a fool believes, he sees, no wise man has the power to reason away.
My point is that one of those things is *not* its size.
What a fool believes, he sees, no wise man has the power to reason away.
... since the orbit of Pluto crosses that of Neptune and therefore Neptune has not cleared out its region of space yet, and probably never will.
Seriously, these IAU definitions are just plain silly and have no hard scientific basis.
The astronomers really ought to create themselves a technical system of classification for scientific use which allows a body to be several things at once, and leave the lay public to their sloppy (but not unreasonable) traditional names for things.
The whole concept of planet is broken, Earth is more like Pluto than Jupiter, it more like many of the moons of Jupiter than the Jupiter and yet the Earth and the Jupiter are classed as the same thing and Pluto and the Earth are not. The answer to how many planets does the solar system have is 4 Gas Giants 4 Rocky bodies that dominate there orbit and hundreds maybe thousands of other objects with enough mass for the gravity to make them round.
The (IAU) definition also includes "is in orbit around the Sun,"
That means that there is no such thing as a planet outside the solar system.
Hey thats why the term exo-planet was invented.
Wow, nearly 6 yrs. ago, I was given an exclusive with the doggy little planet that wasn't.
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To all you astrophysicists, astronomers, geeks, nerds, technophiles, astronaughts, cosmonaughts, astrologers, pagans/neo-pagans, and skywatchers all alike:
Does it really, truely matter what Pluto is classified as? Classification is simple once we had time to research it. Seeing as how we still keep stumbling over whether or not it's a planet, dwarf planet , comet, or binary planet, my guess is we need to really re-think the classification of a planet and what forth. With so many objects in the night sky, there is bound to be thin lines between classes. that's where sub-classes come in.
How do you solve that problem? Simple: add one more criteria to classing whether and object is a planet or not - Did it ever, does it, or could it harbor life of any kind? If you believe modern astronomy, the earth is habited and Mars may have been full of life during our solar system's history. There could be life on Titan, so that goes from being a Moon to being a Planet, to me.
While you're bickering over the classification of Pluto, I'm wondering why the hell aren't we figuring out a better way to get to and fro between all of these objects? Somebody, for the love of God, develop a feasible Ion Drive that cuts our travel time by at least a quarter.
No, the problem is that if you make being a spheroid sufficient to call an object a "planet" (that, and orbiting the Sun rather than another planet), then instead of 9 planets, suddenly you get a bunch more because you'll have to reclassify the other spheroid sun-orbiting objects (now called "dwarf planets") as full-fledged planets, including Ceres, Eris, Haumea, and Makemake. Don't forget a few other: Orcus, Quaoar, Sedna, and 2007 OR10, which may very well be classified dwarf planets soon, and there's probably more out there we haven't found yet (that latest one was just discovered in 2007), so we'd be teaching kids increasing numbers of planets all the time.
Even if we kept the "dwarf planet" designation and set Pluto as the lower limit, Eris is both larger and more massive than Pluto so we'd still have 10 planets (until any larger ones are discovered way out where Eris is).
No, "exoplanet" is for planets which orbit other stars. What you're thinking of is a "rogue planet", which is a planet that doesn't have a star and just floats through interstellar or intergalactic space. These of course are only theorized.
No, they wouldn't. They'd be "dwarf planets", at least most of them would, they're really not that large. Even Titan is only half as massive as Mercury (though it has larger volume), so I'm not sure where it'd rank according to the current definition.
It is not *the* definition, it is a *stupid* definition.
As Abe once said, calling a tail a leg does not make it a leg; the dog still has only four legs.
The IAU coming up with a generally useless new definition for a word that is very much in common usage with a different meaning only shows that the IAU is capable of tremendous hubris, and is not in the service of increasing or distributing knowledge. Quite the opposite.
Will
You could argue that Sun-Jupiter is some kind of Binary, based on that definition. You need something that enforces a near-equal mass - and by near-equal, maybe order of magnitude mass. Whether you write that as it, or abstract it - like having the barycentre greater that ?.2*orbital radii(or semi-major axis) from either planet.
The truth is, we don't have any closely-studyable examples of something we would really describe as a binary planet. Some asteroids are in binary systems, I think, but nothing substantial. When we are clear that we have a binary planet somewhere - or better still, several examples, so we know what is typical - we can make that the 'reference specimen', to borrow from biology. Until then, happity guessing.
Prediction for end of Universe #42: Fencepost error in Quantum_bogosort.cpp
If, in 1930, we knew that Pluto was that small, and there was that many other kuiper belt objects out there, we would never have named a 9th planet. Just like we would never have named the first asteroids the 9th, 10th and 11th planets if we knew the situation when we found them.
But we miscalculated Pluto's mass based on a theory that was found to be based on incorrect math, and didn't know that Kuiper belt existed, so made a mistake. Opps, our bad, fixed now.
Prediction for end of Universe #42: Fencepost error in Quantum_bogosort.cpp
You mean 9 planets.
Earth is no longer considered a planet.
Seems Useless Now?
Prediction for end of Universe #42: Fencepost error in Quantum_bogosort.cpp
[...] causing the duo to orbit a barycenter [...]
All objects orbiting orbit their mutual barycenters, as adjusted by the influence of all other gravitational (or other forces) in the universe. The Earth and Luna orbit their mutual barycenter of gravitation too, so what you've got here, in wanting to re-re-classify Pluto to "binary planet system member" is the creation of a false dichotomy. The only difference is that MAYBE, the barycenter in the case of the Earth/Luna system might be INSIDE the region of space taken up by the Earth at any given moment, but that is basically splitting hairs. For any object NOT to influence the course through space of the object it orbits would imply an action (or force) without an equal and opposite reaction or counter-force. To illustrate, if you had a star such as the sun, and fired a bullet (of approximately 6 grams mass) into orbit around it, the bullet would exert force on the sun, and the sun on the bullet, such that they would orbit their mutual center of gravitation, and the bullet's mass would cause the star to wobble.
Now, it is probably the case given the EXTREMELY LARGE difference between the masses of the sun and a 6 gram bullet, that the difference between the geographical center of mass of the solar system, and the barycenter of the sun-bullet system might well be less than a planck-length apart, and the wobble might be immeasurably small, as I understand classical mechanics the force exists, and it therefore MUST result in a change in momentum, under the laws of motion and of gravity.
But the point is, LEAVE PLUTO ALONE!!! Why do we need to keep changing what it "is"? Pretty soon it's status as a dwarf planet will be revoked, and astronomers and cosmologists will decide it's really an escaped moon of Neptune, or of Saturn, and that Charon was what blew it out of it's orbit, or perhaps it's a bit that split off when whatever blew it out of it's orbit struck it.
So, because of when I learned this stuff, and the fact that it really doesn't matter, I resolve if ever asked how many planets there are in our solar system, I will reply NINE, and include Pluto. Take that, astronomers and cosmologists. I reject your self-appointed authority to change every few years what planets are, and what objects are actually planets.
"Remember kids, the Earth is really just a moon of the sun, which is just a very hot gaseous planet, and the Earth and Luna are really a binary moon/asteroid pair."
See how silly that would sound?
It is the experts WHO DECIDE what a planet is and they simply got around to doing it and it did not take them much effort to kill off pluto; most the hype is the non experts who must be connecting it with the cartoon dog pluto and are reacting as if somebody killed a dog or the cartoon pluto. Or maybe people are just that stubborn to changes in their knowledge?
It is just a rock that ignorantly was called a planet and upon further examination and advances in science is no longer a planet. Get over it! Its like we just found out the world was not flat; because no religions adopted the cause we are not killing people over it. Now if Jesus said pluto was a planet...
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No. Pluto is a dog.
A Binary-DWARF-Planet, maybe, but nevet a Binary-_Planet_.
I suggest two critera: ...
- the already mentioned barycenter-above-the-surface thingy (though this would probably be better expressed by saying that the masses have to be above some 1:10 ratio or something)
- the tidal locking of _both_ bodies to each other (as it is the case in the pluto charon system, but eg. not earth moon - only the moon is tidally locked) which should only be there in a stable configuration as far as I understood the mechanics behind that
What I love about /. is that a topic like this can get almost 200 comments (at the time of this posting).
Most of my friends, even the geekier ones, would go "uh, ok, so what?". Because today "geek" has become to be limited to computers and that was never the gist of it until recently.
Assorted stuff I do sometimes: Lemuria.org
fucking CS academics trying to claim credit for everything now aren't they
Then how is it possible to call them non-scientists?
The only cultural impact is that the culture of America, whose citizen discovered it, no longer discovered the planet Pluto.
It's still out there, it's still called pluto.
It isn't a planet.
The New Testament is given as Truth Absolute. Calvinists think the OT absolute Word Of God, as does the protestant and CoE.
The rank-and-file RCC believe the OT as Word of God too.
They ignore the bits they don't agree with, but everything else they believe absolutely true.
For example, if the OT was merely allegorical, then there was no Original Sin. Therefore nothing for Jesus to die for.
Therefore the Sun/Jupiter system is not a double sun. Therefore Jupiter remains a planet.
And I have no problem with it. Most people who were told Pluto was a planet have no problem with it. Therefore the reason cannot be "because they were taught as kids that there were 9 planets in the Solar System".
Pluto: It's a long way.
Charon: Toss me.
Pluto: What?
Charon: I cannot jump the distance, you'll have to toss me.
The rest is history.
Viewing Pluto-Charon as a prototype binary planet system makes a lot of sense. Why hasn't the IAU considered this? Maybe it's because the IAU planet definition makes no allowance for a binary system. The two planets in a binary by definition haven't "cleared their orbits" of one another. The argument that those of us who continue to view Pluto as a planet do so out of emotion or resistance to change is a straw man argument. Support for dwarf planets being a subclass of planets comes from preference for the geophysical planet definition, in which a planet is any non-self-luminous spheroidal body orbiting a star. Dwarf planets are simply small planets not large enough to gravitationally dominate their orbits. That was the intent of Dr. Alan Stern when he first coined the term "dwarf planet," a term the IAU distorted from its original meaning. Significantly, in astronomy, dwarf stars are still stars, and dwarf galaxies are still galaxies. There is no scientific basis for the argument that Pluto cannot be counted as a planet because that will require many more objects to be also counted as planets. So what? How is there any scientific merit to artificially keeping the number of planets small? No one has a problem with billions of stars or billions of galaxies. No one argues that Jupiter can have only four moons because no one can remember the names of 67. Memorizing is not important for learning. We don't ask kids to memorize the names of all the rivers or mountains on Earth; we ask them to understand what a river and a mountain are. Similarly, we can teach kids the characteristics of each type of planet--terrestrial, gas giant, dwarf planet, etc. Ironically, the demotion of Ceres stands as evidence of a premature erroneous decision, not as a legitimate support for the demotion of Pluto. Ceres was wrongly demoted because 19th century astronomers' telescopes were not powerful enough to resolve it into a disk. Therefore, they couldn't tell that unlike every other object in the asteroid belt (except Vesta and Pallas, which are borderline cases), Ceres is spherical and therefore a small planet with geology and layering. Today, we know the Ceres is spherical and a complex object much more like the larger planets than like any asteroid. The same is true for Pluto. Referring to Pluto as "debris" makes absolutely no sense, as it blurs the important distinction between a complex world layered into core, mantle and crust, with an atmosphere and active geology, and a tiny, shapeless asteroid. Also, it is a misnomer to refer to Pluto as an "iceball," as it is estimated to be 70 percent rock. Pluto is not a comet and will never become a comet. No comet is this rocky or anywhere near Pluto's size. Comets lose mass with every orbit that brings them into the inner solar system. Pluto does not experience any mass loss at perihelion, and it never comes anywhere near the inner solar system. As for the discoverer of Eris, he was for Pluto and Eris being classed as planets before he was against it. His motivation in changing his mind is hardly selfless, as he has sought celebrity status through billing himself as the "plutokiller," getting paid to give talks and promote his book, which is more memoir than science. Interestingly, he was one of three co-discoverers of Eris. One of the co-discoverers, Dr. David Rabinowitz, signed a petition of 300 professional astronomers rejecting the IAU decision. S there is no consensus on the status of these objects even among the discoverer of the one closest in size to Pluto.
Come on.
What was the definition of planet in the past and even now somewhat ? "Some stuff orbiting the Sun we could observe from the earth" and Moons "Some stuff orbiting a planet".
What's the common ground between a gas giant like jupiter and a rocky body with little atmosphere to speak of like Mercury ? nothing. They have nothing in common. They're both called Planets even as of 2012. Because "Planet" is not a word that has a clear cut definition. Saying Pluto's not a planet is just a dick move from people who didn't feel like naming all the smaller objects we found with modern technology orbiting the sun so we're changing the definition of "Planet" rather than fixing a mistake. Calling Pluto a planet was not a mistake with the old definition of planet.
The new definition of planet actually makes less sense than the old I think. Planet used to mean something, that was a bit too all encompassing if your goal is to make a catalog of all things called "Planets" (a daunting task) but at least it made sense. The new definition of planet is completely arbitrary and doesn't define in a clear cut way what a planet actually is.