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Can We Call Pluto and Charon a 'Binary Planet' Yet? 115

Posted by timothy
from the complex-gyrations dept.
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".
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Can We Call Pluto and Charon a 'Binary Planet' Yet?

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  • Admit it. (Score:4, Funny)

    by Anonymous Coward on Friday August 08, 2014 @06:13PM (#47634033)

    You're just trying to troll Neil Tyson for the hilarity that ensues.

  • by turkeydance (1266624) on Friday August 08, 2014 @06:13PM (#47634035)
    seriously....call Pluto what it is...ClickBait.
  • by Anonymous Coward on Friday August 08, 2014 @06:18PM (#47634067)

    We should launch an expedition to reactivate the Charon mass relay.

  • by mi (197448) <slashdot-2012@virtual-estates.net> on Friday August 08, 2014 @06:19PM (#47634075) Homepage

    The debate as to whether Pluto is a planet or a dwarf planet rumbles

    What's with this "dwarf" nonsense — and big planetarism [slashdot.org]? We demand equal gravity for all planets [thepeoplescube.com]!

  • by Anonymous Coward on Friday August 08, 2014 @06:20PM (#47634077)

    I can't believe that this is still an issue. Guess what? IT DOESN'T FUCKING MATTER! This sort of pathetic taxonomic squabble is pointless, and just takes time and attention away from investigating real astronomical phenomenon and making real discoveries.

    It's like those people who claim that JavaScript is a good programming language. There's nothing to debate. JavaScript is total, indisputable shit. It's a pointless argument to get into, because those claiming that JavaScript is good have already lost.

    Astronomers and other scientists, please focus on furthering our knowledge of the universe. Don't waste time with stupid arguments over irrelevant issues like this.

  • by Anonymous Coward on Friday August 08, 2014 @06:23PM (#47634099)

    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...

    • by Anonymous Coward on Friday August 08, 2014 @06:26PM (#47634117)

      Well, if these Jupitarians have their way, Earth will be reclassified as a dwarf planet any day now.

      • Re:Self-awareness (Score:5, Insightful)

        by Smauler (915644) on Saturday August 09, 2014 @06:30AM (#47636581)

        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.

    • by Anonymous Coward on Friday August 08, 2014 @07:00PM (#47634379)
      75-percent is not what I'd call "very nearly"
    • by Noah Haders (3621429) on Friday August 08, 2014 @07:22PM (#47634645)
      the best question:

      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.
      • by Anonymous Coward on Friday August 08, 2014 @07:49PM (#47634819)

        You are just trying to get /. to do your astro homework for you...

      • by bondsbw (888959) on Friday August 08, 2014 @07:56PM (#47634849)

        320,000 miles

        • by bondsbw (888959) on Friday August 08, 2014 @08:03PM (#47634883)

          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.

          • by Noah Haders (3621429) on Saturday August 09, 2014 @12:50AM (#47635861)
            huh I had assumed that the barycenter would move to the surface as the moon got closer, but thinking about it more I see that you're right it would need to move further away.

            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 the mechanism.

            I guess a second question would be, is there a certain distance at which the moon would escape earth's gravity? I wonder what it is, esp compared to the current distance away? would it be 2x, or 10% or 10x?

            greatly appreciate your thoughts, I don't know much about this.
            • by bondsbw (888959) on Saturday August 09, 2014 @03:36AM (#47636259)

              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 is not perfectly circular, but slightly elliptical). When the moon is at its closest, the tides are barely higher, and at its furthest the tides are barely lower.

              I guess a second question would be, is there a certain distance at which the moon would escape earth's gravity? I wonder what it is, esp compared to the current distance away? would it be 2x, or 10% or 10x?

              Gravity accelerates two objects toward one another, based on their mass and their distance. It works the same whether the two objects are initially moving toward each other or away from each other (away from each other, we usually call "decelerating", but there's no difference in the math).

              Escape [wikipedia.org] technically occurs when the two objects are moving away from each other, but the deceleration due to gravity will never be enough to overcome their initial velocity at their initial distance from each other. Gravity diminishes as the objects move farther apart, which results in less deceleration over time. In the case of escape, the velocity will never reach zero.

              The answer is "yes"... assuming the moon magically appeared at that new farther distance but traveling at the same velocity as it is currently. According to the Wikipedia link on escape velocity:

              The escape velocity at a given height is (square root of 2) times the speed in a circular orbit at the same height

              Also, the orbital velocity of an object decreases as its distance increases. So increasing the distance of the moon would decrease how fast it would need to be going to stay in orbit.

              But remember that the orbital distance suddenly increased but the orbital velocity did not change...

              Let's say the moon is orbiting at distance R with orbital velocity V. 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).

              This page contains the formula we need. [wikipedia.org] Solving for r, r is proportional to 1/(v^2). So R2 is proportional to 1 / (V2^2), and substituting the equation above we find that R2 is proportional to 2 / (V^2), which equals 2 * (1/V^2), which equals 2 * R. R2 = 2*R.

              Thus the answer is "2 times the original orbital distance, 478,000 miles".

            • by Smauler (915644) on Saturday August 09, 2014 @06:36AM (#47636589)

              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).

    • by Anonymous Coward on Friday August 08, 2014 @07:31PM (#47634689)

      The barycenter of the Jupiter-Sun binary is above the surface of the sun.

    • by bondsbw (888959) on Friday August 08, 2014 @07:46PM (#47634803)

      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?

      • by robbak (775424) on Saturday August 09, 2014 @04:13AM (#47636331) Homepage

        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 than Charon, so 'Planet/moon system' defines it better. If we start to find real binary planet systems outside of our solar system and stat characterizing them, then we will be able to know what sorts of systems happen and how they form, and maybe then we will find that Pluto/Charon belongs as an outlier there. But that's for a future time.

        • by bondsbw (888959) on Saturday August 09, 2014 @12:37PM (#47637627)

          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 binary planet. It would be considered a binary planet if the smaller body has a concave orbit around the sun; in other words, the two are both primarily orbiting the sun and just happen to be close to each other. This would, however, define the earth/moon system as a binary planet and Pluto/Charon would be a planet/moon.

    • by Will.Woodhull (1038600) <wwoodhull@gmail.com> on Saturday August 09, 2014 @01:48AM (#47636011) Homepage Journal

      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).

    • by russotto (537200) on Saturday August 09, 2014 @10:02AM (#47637141) Journal

      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...

      That's no moon! (Ask David Weber)

  • by Henriok (6762) on Friday August 08, 2014 @06:27PM (#47634121)
    The arguments for demoting Pluto from its planetary status still holds. And hardly anyone objects to Pluto and Charon together as a binary system. But this "new" insight does not promote Pluto/Charon to planetary status. Binary dwarf planet, binary kuiper belt object, binary plutoid. Absolutely. Binary planet? No.
  • Pluto is a Planet (Score:1, Insightful)

    by sexconker (1179573) on Friday August 08, 2014 @06:27PM (#47634127)

    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.

    • by retchdog (1319261) on Friday August 08, 2014 @06:34PM (#47634177) Journal

      christ you're an unusually stupid fuck.

      anyway, please tell me what's wrong with nonflammable. this ought to be entertaining.

      • by sexconker (1179573) on Saturday August 09, 2014 @03:18PM (#47638379)

        "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.

    • by Anonymous Coward on Friday August 08, 2014 @06:39PM (#47634203)

      "I think I know what the A in NASA stands for." Jerry Smith

    • by The Evil Atheist (2484676) on Friday August 08, 2014 @09:30PM (#47635239) Homepage
      There was no definition of planet, that was the point. Dictionary definitions don't count, because the dictionary definition would include asteroids, comets, the sun and moons. If you want those included in the planet category, go study Indo-European astrology.
    • by wonkey_monkey (2592601) on Friday August 08, 2014 @09:43PM (#47635285) Homepage

      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.

      • by retchdog (1319261) on Friday August 08, 2014 @10:57PM (#47635533) Journal

        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.

      • by sexconker (1179573) on Saturday August 09, 2014 @03:26PM (#47638421)

        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 reasons for using binary bases, the SI and other such organizations do not own the letters "kilo" not the letter k, such organizations have ambiguity in their own fucking rules, such organizations are not authorities for the language, and the big kicker, of course, is that the units in question aren't kilo, mega, etc, they're kiloBytes, megabits, etc. - there's never any ambiguity because you always have bits or bytes right there. And before you get started on trying to pull out some "gotcha" example where someone mixes them up: modems are rated in baud, not bits, storage manufacturers are liars who caused the mess in the first place, and I don't give a shit about how we have 1000 mbps ethernet or other such standards - it has no bearing on anything. Try again when we have memory measured in "gibibytes" or bus widths in factors of 10.

        • by akozakie (633875) on Saturday August 09, 2014 @05:43PM (#47638995)

          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...

        • by wonkey_monkey (2592601) on Saturday August 09, 2014 @06:15PM (#47639139) Homepage

          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 definition was no longer fit for purpose. The two things are different. The IAU weren't out to force their new definition of "planet" on the man in the street. They're a scientific organisation, and for their purposes it was decided that it would be better to introduce the new limits on what should be a called a planet in formal scientific discussion than to start adding a load of newly-discovered Kuiper Belt object to the list.

          No-one's trying to stomp on "your" definition of a planet. Why are you so upset about their's?

          For inflammable, look up the Latin roots inflammare and flamma.

          I know what the problem with "inflammable" is, but you did originally say "non-flammable." Bit ironic in the circumstances.

          PS Swearing doesn't really do any favours in getting a point across, even if someone has a reasonable one to make. It just makes the petitioner sound butthurt.

    • by Beck_Neard (3612467) on Friday August 08, 2014 @10:13PM (#47635401)

      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?

      • by sexconker (1179573) on Saturday August 09, 2014 @03:32PM (#47638453)

        And I would consider them planets.

        • by Beck_Neard (3612467) on Saturday August 09, 2014 @09:00PM (#47639819)

          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 to call the former ones 'planets' and the latter ones 'dwarf planets'. Plus, 'dwarf planet' has an additional benefit that it gives you a mental idea of being small (relatively speaking).

          But think about what would happen if they were all just called 'planets'. Inevitably people would come up with ad-hoc terms like 'main planets' or 'large planets' to refer to the 8 planets. It would be extremely confusing. That's another thing about language - it evolves largely on its own. We can't 100% influence it; we can only take steps to try to steer its evolution in a slightly better way.

    • by knorthern knight (513660) on Sunday August 10, 2014 @03:43PM (#47643143)

      > 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 given their own class. Similarly, there are now almost 1300 http://www.minorplanetcenter.n... [minorplanetcenter.net] known objects in Pluto's vicinity. If you want to think of the solar system having 1300 planets, be my guest.

      Scientists occasionally make mistakes, based on incomplete data. When more info becomes available, they correct those mistakes. E.g. they junked the Aether theory http://en.wikipedia.org/wiki/A... [wikipedia.org] after the Michelson-Morley experiment.

      There was *ALWAYS* major doubt about Pluto's planetary status. This article from 1934 http://blog.modernmechanix.com... [modernmechanix.com] is an example.

      > So that Pluto ranks as the largest asteroid,
      > rather than the smallest planet;

      BTW, it's worse than the article suggested; Pluto is actually less than 1/10th the mass of Titan.

      > and the dipshits who insist that a kilobyte is 1000 bytes.

      So you think the ancient Greeks were dipshits? And the French who introduced the metric system? The real dipshits are the people who arbitrarily change the meanings of words after thousands of years..

  • What debate? (Score:5, Informative)

    by glwtta (532858) on Friday August 08, 2014 @06:35PM (#47634193) Homepage
    Planet and Dwarf Planet are arbitrary labels defined by the IAU.

    How can you "debate" about that?
  • by glwtta (532858) on Friday August 08, 2014 @06:42PM (#47634225) Homepage

    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?

  • by Anonymous Coward on Friday August 08, 2014 @06:42PM (#47634229)

    I have binary testicles!

  • by Anonymous Coward on Friday August 08, 2014 @06:46PM (#47634245)

    Pluto is a dog planet.

  • by philotag (557239) on Friday August 08, 2014 @06:58PM (#47634347) Homepage
    The barycenter of the Sun and Jupiter is above the surface of the sun, does that mean we'd have to reclassify our solar system as a binary star system now? http://spaceplace.nasa.gov/bar... [nasa.gov]
  • by Anonymous Coward on Friday August 08, 2014 @07:09PM (#47634505)

    Unless Pluto (and Charon) shifted orbit into the planetary plane, nothing has changed and any desire to call it a planet is just sentimentality.

  • by Anonymous Coward on Friday August 08, 2014 @07:09PM (#47634507)

    what the 'A' in NASA stands for...

  • by TheRecklessWanderer (929556) on Friday August 08, 2014 @07:11PM (#47634537) Journal
    Pluto doesn't care what you call it. It's going to be around when you are dust in the wind. Oh and I don't care either.
  • by umghhh (965931) on Friday August 08, 2014 @07:22PM (#47634647)
    what is that? Why not furlongs or Manhattans?
  • by Mister Liberty (769145) on Friday August 08, 2014 @08:28PM (#47634993)

    No phone lines yet. Sorry.

  • by Livius (318358) on Friday August 08, 2014 @10:30PM (#47635457)

    No.

  • by rossdee (243626) on Friday August 08, 2014 @10:39PM (#47635487)

    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

  • by Unknown74 (3041957) on Friday August 08, 2014 @10:52PM (#47635519)
    Uh, folks, Pluto actually has FOUR moons... Charon: Discovered in 1978, this small moon is almost half the size of Pluto. ... Nix and Hydra: These small moons were found in 2005 by a Hubble Space Telescope team studying the Pluto system. Kerberos: Discovered in 2011, this tiny moon is located between the orbits of Nix and Hydra. ...and it just keeps on thumbing it nose at the dwarfists, and now, the binarists. But tell me, how is a FIVE body system a BINARY system? Hmmmmm?
    • OOOps! (Score:4, Informative)

      by Unknown74 (3041957) on Friday August 08, 2014 @11:05PM (#47635553)
      My mistake...Pluto has FIVE moons. Charon: Discovered in 1978, this small moon is almost half the size of Pluto. It is so big Pluto and Charon are sometimes referred to as a double planet system. Nix and Hydra: These small moons were found in 2005 by a Hubble Space Telescope team studying the Pluto system. Kerberos: Discovered in 2011, this tiny moon is located between the orbits of Nix and Hydra. Styx: Discovered in 2012, this little moon was found by a team of scientists search for potential hazards to the New Horizons spacecraft flyby in 2015. may the 'little planet that could' keep right on thumbing it nose at everybody!
  • by slashdot_commentator (444053) on Sunday August 10, 2014 @06:06AM (#47641015) Journal

    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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