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Space Science

Is Pluto a Binary Planet? 275

Posted by samzenpus
from the twice-as-fun dept.
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."
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Is Pluto a Binary Planet?

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  • by girlintraining (1395911) on Sunday July 15, 2012 @05:05PM (#40658519)

    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.

    • by starless (60879) on Sunday July 15, 2012 @05:46PM (#40658745)

      Why do you call the committee members pseudo-scientists? I'm rather sure everyone has a PhD in astronomy/astrophysics. (I'm technically an IAU member, although I've had little involvement with it.)

    • by lennier (44736) on Sunday July 15, 2012 @06:52PM (#40659097) Homepage

      But then, I'd expect nothing less from a committee of pseudo-scientists

      You, sir, have very low expectations for the noble profession of pseudo-science. I both demand and expect a whole lot more from my committees of space pseudo-scientists:

      1. At least three separate and conflicting theories about the catastrophic formation of the solar system as a result of an interplanetary war between four and eight thousand years ago.
      2. A dozen formulations of the Lorentz Contraction as a result of the pre-Einsteinian ether
      3. A gigantic laser mounted on Mimas [wikipedia.org]
      4. A baroque dying Martian civilisation clustered in glorious decadent splendour among the Red Weed entwined canals and pentagonal pyramids of Cydonia.
      5. Ancient space Egyptians and Mayans with lasercats.
      6. Space Mormons versus robots.
      7. A literary analysis of Shakespeare's Hamlet as really being about the precession of the equinoxes.
      8. An apocalyptic prediction involving Halley's Comet.
      9. An Electric Universe theory, preferably one that makes Saturn a former star.
      10. A homebuilt antigravity demonstration device harnessing the awesome power of magnets.

    • Re: (Score:3, Insightful)

      by osu-neko (2604)

      It's a far cry from the organization's original role: Cataloging astronomical objects.

      Um, no. Deciding upon definitions is an absolutely necessary part of doing precisely that job.

    • by mrmeval (662166)

      It's all about consensual science. It's what the majority believe. Pluto is not a planet, all that junk is just debris. It is also a shifting science in that if you can change consensus you can change the facts.

    • They don't actually move the books around

      That'd be kind of cool. The solar system really is very disorderly when you think about it - particularly Pluto with its lopsided orbit. They should fix that. And maybe sort them by size while they're at it.

  • by n5vb (587569) on Sunday July 15, 2012 @05:06PM (#40658523)

    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

    • by arth1 (260657)

      As closely as they orbit each other, I'd say Pluto-Charon would be almost the example of such a system.

      Close? It's precisely because Charon is so far away[*] that the barycenter is outside Pluto's surface. If it had been closer, the barycenter would have been inside Pluto.

      If it had been closer, you would call it a moon, but because it's further away you call it a binary system? That doesn't make sense to me.

      [*] Almost twice as far away from its barycenter as Phobos is from its barycenter inside Mars, for example.

      • by edremy (36408)
        Worse, Earth's moon is slowly moving away from the center of the Earth due to tidal effects. At some future point the barycenter of the E-M system will be outside the surface of the Earth, and which point Earth becomes a binary planet as well.
        • 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 substa

  • Sun is the same way (Score:5, Informative)

    by mister_playboy (1474163) on Sunday July 15, 2012 @05:08PM (#40658533)

    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.

    • Re: (Score:2, Insightful)

      by Anonymous Coward

      Wouldn't Jupiter need to be a star? Short of us igniting it, I think that is going to be a problem.

      • Damn! You're right! Where's Arthur C. Clarke when you need him...
      • Re: (Score:3, Informative)

        by Kickasso (210195)

        Well, it does radiate more energy than it gets from the Sun...

        • by siddesu (698447)
          But that is not due to nuclear reactions in the core, as would be the case with a star. And it is too small to even be a brown dwarf.
      • Jupiter may already be burning; if there was a self-sustaining nuclear reaction at its core, that would explain some of its puzzling activity. The idea of brown dwarf stars is not a new one: stars that do not emit much if any visible light, but pump out heat and particles.

        • by Chris Burke (6130)

          Jupiter may already be burning; if there was a self-sustaining nuclear reaction at its core, that would explain some of its puzzling activity.

          That would cause many more problems (particularly in nuclear theory) than it solves. Jupiter's heat output is easily explained by gravitational binding energy.

          The idea of brown dwarf stars is not a new one: stars that do not emit much if any visible light, but pump out heat and particles.

          "Brown dwarf star" is not a thing. Brown Dwarves are by definition sub-stellar objects. They are not massive enough to sustain fusion reactions. The current definition puts the minimum mass much higher than Jupiter, though the boundary between brown dwarf and large planet is a fuzzy one. The boundary between brown dwarf and star, however, is muc

      • by cyn1c77 (928549)

        Wouldn't Jupiter need to be a star? Short of us igniting it, I think that is going to be a problem.

        You could consider it a brown dwarf, if you could get the IAU to lower the minimum brown dwarf classification mass.

    • by mooingyak (720677) on Sunday July 15, 2012 @05:35PM (#40658697)

      If the mass part counts at all (Charon being 12% of Pluto's mass), Jupiter is a far smaller fraction of the Sun's mass (something like 0.1% if I did the math right).

    • by arisvega (1414195)

      After all, Charon is 12% the mass of Pluto

      The barycenter of the Sun/Jupiter system [..] Is the Sun a binary star?

      Jupiter is less than 0.1% the mass of the Sun

    • by Hentes (2461350)

      Depends on how do you define the radius of the Sun.

      • Most people would consider the radius of the Sun to end where the mass of burning fusion ends, which is fairly constant except for solar flares... though I do get your point. If we include the atmosphere in our calculation of the solar radius, then Jupiter is actually within the heliosphere.

        • by Anonymous Coward

          Sorry, this is wrong. Fusion only occurs in the core. The radius of the son is considered to be the photosphere, even though it is acknowledged that the corona (sun's "atmosphere") extends far beyond that.

        • by cyn1c77 (928549)

          Most people would consider the radius of the Sun to end where the mass of burning fusion ends, which is fairly constant except for solar flares... though I do get your point.

          If you did that, the solar radius would be 25-30% of the accepted definition!

    • by arth1 (260657)

      Yes, the Earth/Moon barycenter is within the earth - right now. But the moon recedes, currently around 2.2 cm per year, which means that the barycenter is going to be outside the earth's surface in a few thousand million years.

      And this is what's wrong with using the barycenter as part of judging whether it's a binary system or a moon - the further away the two objects are, the further away from the heavier object the barycenter will be. So you can have two identical planets with two identical satellites,

      • Re: (Score:3, Informative)

        by Anonymous Coward

        Some people also consider the Earth/Moon to be a binary planet. The Sun's hold on the moon is actually greater than the Earth's, and so if you were looking at the Moon's path in the solar system it is always concave to the Sun. The path of any other moon in the solar system is sort of zigzaggy, sometimes moving towards the Sun and sometimes away, depending on its location relative to its planet.

        Wikipedia probably explains it better: http://en.wikipedia.org/wiki/Double_planet
        http://en.wikipedia.org/wiki/Orbi

    • Re: (Score:3, Interesting)

      As far as I know, the question of whether Jupiter is producing energy through some core fusion or fission process remains unresolved. Jupiter might well be reclassified as not a planet, but as a dwarf brown star.

      So perhaps we are in a binary star system.

      Furthermore, the Earth's orbit is so strongly perturbed by the Moon that the time of perihelion shifts over more than 24 hours from year to year, depending on where the Moon is in its orbit on Jan 3 through 5. This is an angular variance of about 1 degre

  • by Megahard (1053072)
    The Death Star was so massive that when it orbited a planet it became a binary system.
    • by spire3661 (1038968) on Sunday July 15, 2012 @05:26PM (#40658645) Journal
      Ugh. The entire idea of the 'death star' shows how little imagination Lucas has. Even moving the death star into a system would effect the planetary orbits. Why would you need a big laser gun when you can simply wobble a planet out of its habitable orbit using the gravity of your space station.
      • by siddesu (698447)
        True of all doom weaponry in most sci-fi movies. It has to look good on screen, not to be scientifically plausible. The audience of the star wars movies are the 7-14 y.o. children, after all.
      • by idji (984038) on Sunday July 15, 2012 @05:51PM (#40658781)
        because you want results in seconds, not aeons.
      • by n5vb (587569)

        Ugh. The entire idea of the 'death star' shows how little imagination Lucas has. Even moving the death star into a system would effect the planetary orbits. Why would you need a big laser gun when you can simply wobble a planet out of its habitable orbit using the gravity of your space station.

        Wouldn't take much, if you pick the right resonant orbit and aren't in a hurry .. ;)

      • by canajin56 (660655) on Sunday July 15, 2012 @06:18PM (#40658889)
        The first death star was 160 KM in diameter, so a radius of 80 KM. If you assume the same mass density as, say, an aircraft carrier or other military vessel (about 0.15 kg/m^3), you end up with a Death Star that masses about 3e14 KG. That's absurdly heavy to realistically have engines zipping it about, but it's not going to result in major and instantaneous disruptions of orbits. Even Mars' tiny moon Phobos has 100 times the mass. Although the Death Star II from RotJ was supposed to be 900KM across, so that would put it about even with the mass of Phobos. Put another way, the Earth masses 10,000,000,000 times as much (or only 100,000,000 for the Death Star II), so I don't see how the Death Star is going to be winning that gravitational tug-of-war. If you want to argue "Well maybe they have super cool tractor beams so they can amplify their gravitational pull and their massive engines can keep them stationary while they're doing it!" the obvious counter is "They don't, that's why they went with the laser, since they thought about it. Also big laser is more menacing in a platform which has the primary purpose of intimidation. Additionally the big laser doubles as a way to destroy enemy capital ships from well outside their own engagement radius".
    • "The Death Star was so massive that when it orbited a planet it became a binary system."

      But of course it's a binary system: that's no moon.

  • by Anonymous Coward on Sunday July 15, 2012 @05:19PM (#40658603)
    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.
  • by TheGoodNamesWereGone (1844118) on Sunday July 15, 2012 @05:28PM (#40658653)
    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.
    • by spire3661 (1038968) on Sunday July 15, 2012 @05:51PM (#40658777) Journal
      Humans fear all change.
    • by Anonymous Coward on Sunday July 15, 2012 @06:09PM (#40658847)

      "Is it something more personal between individuals in astronomy?"

      This, actually. Long story short, there are two camps of astronomers. One of them characterizes bodies based on where they're orbiting, the other characterizes bodies based off what they're made of.

      The former pushed this through as an act of political dickmanship on the last day of a conference (after most participants had gone home), in a only tangentially related addition to a talk scheduled for a different topic, breaking IAU rules to do so. It's not a 'scientific' decision, it's a purely political one.

      And any definition that has a category 'dwarf planet' that isn't a subset of 'planet' is about as stupid as redefining 'car' so that 'electric cars' are no longer a subset of 'cars'.

      • by TheGoodNamesWereGone (1844118) on Sunday July 15, 2012 @06:45PM (#40659051)
        I figured it had something to do with dick-waving. I'm not a professional astronomer, don't play one on TV, but I've had an abiding love for the subject since I was growing up in the 60s. If you use the orbital argument then it makes sense, because Ceres, too was thought to be a planet in 1801 (It accorded nicely with the 'traditional' Bode's Law). It didn't take long for the scientific community to figure out thought, after Vesta, Juno, and other asteroids were found that these were just the largest members of a population of many; we now estimate hundreds of thousands. Likewise the compostional argument works in favor of demotion as well. Working outward we have rocky inner planets, two gas giants, two ice giants, and then a buttload of comparitively very tiny solid icy bodies, that when they get perturbed and wander closer, get called comets. I don't understand the emotion behind the debate. in 1801 the asteroid belt wasn't known, so they called Ceres a planet. In 1930 the Kuiper belt wasn't known, so they called Pluto one. We've learned differently. What's all the fuss?
        • by Iskender (1040286) on Sunday July 15, 2012 @10:50PM (#40660251)

          Likewise the compostional argument works in favor of demotion as well. Working outward we have rocky inner planets, two gas giants, two ice giants, and then a buttload of comparitively very tiny solid icy bodies, that when they get perturbed and wander closer, get called comets. I don't understand the emotion behind the debate.

          The best idea of what to do with the planet definition I've seen so far is to scrap it. Planets are originally things that move about in the sky. Now it's used for something or other because we're not comfortable with the now thousands of planets that exist under the old definition.

          There are several problems with the kinds of planets you mentioned. Currently a planet is (in practice): 1) A rocky round body OR 2) A large gaseous body OR 3) A large gaseous "icy" body. The problem being that if you take a large KBO, Mercury and Jupiter, the two planets certainly will not have the most in common (radii about 1000, 2500 and 69000 km, respectively.) It's possible to build a definition that includes only eight planets, but it will give you a collection of bodies that have nothing else in common.

          The planet definition is temporary in any case since it specifically doesn't apply outside the Sol system. I think the science should really throw it away as far as it can, so that the public can use the word however it wants without science being disturbed, while astronomers could stop playing unnecessary politics.

      • by bryan1945 (301828)

        That, and the one camp likes cats more than dogs.

      • by Xylantiel (177496)

        First -- what you have said has nothing to do with the question of why people are so stuck on Pluto. I think this comes down to people not understanding science. They think science is "right", which is good, but of course "early" science is often wrong. There is a whole hierarchy of confidence levels, and things of low confidence often turn out to be wrong -- like the long-disproven notion that Pluto is a 9th body much "like" the other 8 planets. Turns out Pluto is just the largest Kuiper belt object a

    • by Baloroth (2370816) on Sunday July 15, 2012 @06:25PM (#40658929)

      To say it "never was a planet" is not quite true. It never was a planet according to the definition of planet that we use now, but it was a planet according to the definition we used to use. If you change the definition, people are going to be confused. It has nothing to do with tradition (except insofar as language is a "tradition"), and everything to do with the alteration of the language. Now, that alteration may be fully scientifically justified and acceptable... but it's still going to annoy people.

      The comparison with the geocentrism is a little faulty. The issue here has very little to do with our knowledge of reality changing (it didn't really), but with the way we look at that reality changing (i.e. the words used for a thing).

      It's not science, it's linguistics. The result is even now what category Pluto falls into can be debated: we could quite easily call it a planet even now, the problem is the definition would be too wide and force us to call things planets not traditionally called planets. So somewhat contrary to your point, a large part of the reason Pluto isn't called a planet anymore is actually tradition: because we don't want to call all the Kuiper belt objects planets also.

      • Re: (Score:2, Informative)

        by Anonymous Coward

        It's even weirder when you consider that even now, the IAU agrees that Pluto is a dwarf planet. It's just that their change was to make it so that a dwarf planet is not called a planet. It's a very, very odd linguistic or logical choice to make and yet you can find information online about some of the rather severe political tactics used to ensure the change was made.

      • 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.

    • by Sarten-X (1102295)
      A lot of money was wasted making those silly 9-letter acronyms to be printed in hundreds of thousands of textbooks, and now they all have to be redone! The economic burden is astronomical.
    • by styrotech (136124)

      Is it because children have to be sat down and gently told the truth, like about Santa Claus?

      Now that you mention children - my five year old is in denial. He still insists that Pluto is a planet. Even if the reclassification was just before he was born. The set of plastic planets hanging from his ceiling (his first ever Solar System experience) included Pluto, and no new library book or educational dinner table placemat since has managed to convince him otherwise.

      I'm sure he would be far less upset after l

    • by Grishnakh (216268)

      Everyone's pissed because they were taught as kids that there were 9 planets in the Solar System, and that the last one had the same name as one of their favority Disney characters. So they're mad that it's been demoted to "dwarf planet", even though they never had a problem before with Ceres being classified that way, and Ceres is much, much closer to us.

  • by christurkel (520220) on Sunday July 15, 2012 @05:30PM (#40658663) Homepage Journal
    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.
    • and the components of the system are similar in size and/or mass.

      How similar is "similar"?

    • You've now created a new classification by omission. What about formerly binary star systems where one entity far more massive? I like your definition though.

  • No (Score:4, Informative)

    by gman003 (1693318) on Sunday July 15, 2012 @06:06PM (#40658829)

    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.

  • No. Pluto is a dog [wikipedia.org].

  • off-topic (Score:4, Insightful)

    by Tom (822) on Monday July 16, 2012 @02:43AM (#40660977) Homepage Journal

    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.

I have never seen anything fill up a vacuum so fast and still suck. -- Rob Pike, on X.

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