Pluton or Planet?

|

Scientists at the annual meeting of the International Astronomical Union are apparently going to vote to let Pluto remain a planet and promote scores of similar bodies to that status. The proposed definition of a planet is:

"A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet."

However, to make a distinction between the "classical" inner planets like the Earth, Jupiter and so forth, these smaller planets will also be called "plutons" with Pluto having the honor of being the first such celestial object discovered.

Does it make much of a difference calling one object a planet and another a pluton? As philosopher Ludwig Wittgenstein argued in his Philosophical Investigations: "Think of the tools in a tool-box: there is a hammer, pliers, a saw, a screw-driver, a ruler, a glue-pot, glue, nails and screw.—The functions of words are as diverse as the functions of these objects." The just as the word tool encompasses hammers, saws, and so forth, now the word planet encompasses plutons.

It's unlikely that schoolchildren will have to memorize the names of scores of new planets, uh plutons. After all how many of you can name all of the known moons of Saturn and Jupiter off the top of your head right now?

NEXT: The Forever War

Editor's Note: We invite comments and request that they be civil and on-topic. We do not moderate or assume any responsibility for comments, which are owned by the readers who post them. Comments do not represent the views of Reason.com or Reason Foundation. We reserve the right to delete any comment for any reason at any time. Report abuses.

  1. I’m no astronomer, but I’m not aware of any reason why this distinction matters. What’s interesting is not the name “planet”, but rather the fact that our solar system contains 3 distinct types of large objects orbiting the sun: The terrestrial inner planets, the gas giants, and then Pluto-sized objects. That’s interesting.

  2. I wish I understood about Planets and black holes and all that cosmic stuff. Unfortunatley, I’m too dumb.

    Still, hopefully when I’ll die they’ll be able to cryogenically freeze me and bring me back in a time when teleports are invented and people are living on Mars and Pluto. It would be so awesome.

    Concerning Ludwig Wittgenstein. I tried reading his Tractatus. Absolute gobbeldygook. Although I am aware that I’m probably too dumb to understand this aswell.

    After all how many of you can name alll of the known moons of Saturn and Jupiter off the top of your head right now?

    I love that line in Manhattan when Woody Allen and Keaton are in the Planitarium and she recalls all the moons of Jupiter and he reminds her that the brain is the most overrated organ. Woody is right on that one. He’s still a sex pest though.

  3. If they do end up creating a category named “Pluton,” I wonder what Spanish-speaking astronomers are going to do: the name for Pluto in Spanish is already “Plut?n.”

  4. From what I read elsewhere, the new definition makes Ceres and Xena planets. Here

  5. I wonder if that would make Ceres a planet as well. It’s pretty small, but it meets the new defition.

  6. Ceres will be counted as a planet, as will Charon and of course Xena. (This debate started because Xena seemed to be more worthy of inclusion as a planet than Pluto.) However, don’t count on Xena retaining its name; it’s still officially called 2003 UB313. Here’s the new order of planetary battle. Given Ceres’ position and the news that “more planets are to come,” I presume that means new promotions will be coming in the asteroid belt? It seems to me this doesn’t affect the definition of a planet so much as the definition of an asteroid.

    Pluto retains the distinction of being the first planet detected in theory before it was observed in practice. I say as long as Uranus is open, everything’s OK.

  7. Charon orbits Pluto, so it seems it wouldn’t get promoted. Right?

    “is in orbit around a star, and is neither a star nor a satellite of a planet.”

  8. “Pluto retains the distinction of being the first planet detected in theory before it was observed in practice.”

    That’s arguable. Neptune was also “mathematically discovered”, although it had been incidentally observed previously (being incorrectly tagged a star by earlier astronomers): http://www-groups.dcs.st-and.ac.uk/~history/HistTopics/Neptune_and_Pluto.html

    Meanwhile, although Percival Lowell did predict a ninth planet based on his observations of irregularities in the orbit of Neptune, Pluto’s mass is too small to account for those irregularities: http://www1.jsc.nasa.gov/er/seh/neptune.html In other words, Lowell didn’t actually predict Pluto, he predicted a different planet and Pluto just happened to be in the area.

  9. But maybe they consider that Charon and Pluto orbit each other, rather than Charon orbiting Pluto.

    The definitions doesn’t say the joint center of gravity is below the surface of the larger body, but it seems that is how they are applying it to Charon/Pluto.

  10. Ceres was once recognised as a planet and will regain that status under the new definition. As such, Ceres is the first such known planet.

    The argument for declaring Charon to be a planet is based upon a theory that Pluto and Charon are double planets. That is, the similarity in their size is such that some say that they orbit around each other while orbiting the sun rather than constituting a clear planet and satellite. There is another argument, based upon the relative gravitational effect of Earth and the Sun on the moon, that our own planet and the moon are a double planet system.

  11. Ceres was once recognised as a planet and will regain that status under the new definition. As such, Ceres is the first such known planet.

    The argument for declaring Charon to be a planet is based upon a theory that Pluto and Charon are double planets. That is, the similarity in their size is such that some say that they orbit around each other while orbiting the sun rather than constituting a clear planet and satellite. There is another argument, based upon the relative gravitational effect of Earth and the Sun on the moon, that our own planet and the moon are a double planet system.

  12. Ceres was once recognised as a planet and will regain that status under the new definition. As such, Ceres is the first such known planet.

    The argument for declaring Charon to be a planet is based upon a theory that Pluto and Charon are double planets. That is, the similarity in their size is such that some say that they orbit around each other while orbiting the sun rather than constituting a clear planet and satellite. There is another argument, based upon the relative gravitational effect of Earth and the Sun on the moon, that our own planet and the moon are a double planet system.

  13. Ceres was once recognised as a planet and will regain that status under the new definition. As such, Ceres is the first such known planet.

    The argument for declaring Charon to be a planet is based upon a theory that Pluto and Charon are double planets. That is, the similarity in their size is such that some say that they orbit around each other while orbiting the sun rather than constituting a clear planet and satellite. There is another argument, based upon the relative gravitational effect of Earth and the Sun on the moon, that our own planet and the moon are a double planet system.

  14. Ceres was once recognised as a planet and will regain that status under the new definition. As such, Ceres is the first such known planet.

    The argument for declaring Charon to be a planet is based upon a theory that Pluto and Charon are double planets. That is, the similarity in their size is such that some say that they orbit around each other while orbiting the sun rather than constituting a clear planet and satellite. There is another argument, based upon the relative gravitational effect of Earth and the Sun on the moon, that our own planet and the moon are a double planet system.

  15. If we’re not sure it’s a planet, I move we call it a “blypton.”

    BTW, thanks for the hummmm job, Hmmm.

  16. Quintuple post–does that mean we drink four times or three times?

  17. How many can name all the moons of Saturn off the top of their heads ?

    Far more than last year, because the Wall Street Journal listed the top 35
    in an op-ed this spring-

    “A Snowball Under The Sun”
    by Russell Seitz
    The Wall Street Journal…………………………………..March 14 2006

  18. Since Ron has dragged in Ludwig W’s Tractatus, one has a duty to the language to point out that garden variety plutons are bodies of differentiated rock which ,as they are rising through the crust or mantle of the Earth ,are necessarily in geosynchronous orbit about its center.

    Does this mean ‘El Capitan’ and ‘Old Baldy’ are moons as well as rigid designators in the real set ?

    Please advise, Ron, you’re the editor.

  19. KIRK: Take us out of warp, Mr. Sulu.

    SULU: Aye, sir.

    SPOCK: We appear to be in this star system’s asteroid belt. I recommend shields.

    KIRK: Shields up! Begin scanning.

    SPOCK: Excuse me, Captain. I regret that I must inform you that I was mistaken. After further analysis I find that the material of the objects in this belt is unusually warm and ductile, making the larger ones more spheroid than irregular. We are actually in this system’s planet belt.

    KIRK: Do I need planet shields now, Mr. Spock?

    SPOCK: No, no. Nothing different is required from us. It’s just that these things are spherical, so they are planets, not asteroids. Damn you, IAU 2006!

  20. I must say, this proposed definition bites.

    You brought in Wittgenstein, so I’ll bring in Rand. She may have been loopy in how much you could derive from philosophy, but her epistimological notion of concepts and concretes was pretty damn good.

    When you have a collection of objects that have enough similar characteristics that it is useful to group them into a concept, you make a concept that generalizes the common characteristics. For 2500 years we had, “Planets are the bodies that move in the ecliptic against the stationary star field.” We discovered Uranus and Neptune, which looked a lot like the known planets.

    We discovered Ceres, which looked a lot like the known planets, though smaller. Then we discovered hundreds of other objects in Ceres’ orbit and recognized that Ceres’ was simply a large exemplar of a new class of objects that should not be called planets. They are asteroids. Ceres got its planet tag removed.

    Then we discovered Pluto, which looked a lot like the known planets, though smaller, somewhat out of the ecliptic, and pretty eccentric. Now we have discovered a lot more Pluto-like objects further out.

    The proper next step is to remove the planet tag from Pluto, just as it was removed from Ceres two centuries ago. Pluto is more like the highly eccentric, out of the ecliptic, mostly ice KBOs than it is like the known planets. It belongs in a new concept. KBOs don’t belong in the 2500 year old concept “planet”, especially based on a distinction as silly as “they are round”.

    Tombaugh was looking for a planet. He discovered the only KBO so near the sun and so near the ecliptic. Everyone called it a planet. Now that it is evident that it has more in common with KBOs or “plutons” than with planets, Pluto should be called a “pluton”. And the useful concept of planet should not be sullied by adding KBOs that happen to be round into it.

  21. I should add that yesterday I was a “there are nine planets” kind of person, for purely schoolchild historical reasons.

    Then last night I saw this definition, a definition I have been looking forward to since one of the panel members said, “People will like this definition.” Well, I don’t. “Everything round within a light year of the sun” is a hideous definition for a planet!

    I am willing to lose Pluto so as not to gain a hundred plutons.

    Maybe that was the committee’s intent… “You know, Pluto isn’t really a planet.” “You know that and I know that, but a hundred million schoolchildren and their parents will be really ticked off if we demote it.” “I’ve got an idea. Let’s come up with something so stupid that it calls Jupiter and some silly piece of ice 30 billion miles away both planets. Everyone will hate it! Demoting Pluto will seem tame by comparison.” “Excellent! Great idea, Dava Sobel!”

  22. I think that the debate over whether or not to call Pluto a planet illustrates what Feynman said about the difference between knowing the name of something and understanding what it is.

    We now realize that our solar system is a layered system: The inner core has 4 solid planets, in many ways very similar to each other. Then there’s an asteroid belt. Beyond that are 4 gas giants, sharing certain common features. Beyond the gas giants are a large number of rocky objects referred to as “Kuiper Belt Objects”, the largest of which bear some resemblance to the inner planets. These outer objects extend to a considerable distance from the sun.

    Given the differences between the inner planets, the gas giants, and the Kuiper Belt Objects (including Pluto), it would be better to stop talking about a single category known as planets, and instead talk about 3 categories.

    I realize that people don’t want to make such fine distinctions in casual conversation, and that’s fine. But the mere fact that there is so much debate should clue us in that the term “planet” is papering over a wide range of objects, and that there are several distinct categories of objects present. And that should clue us in, once again, on the difference between knowing the name of something and knowing what it is, how it works, and how it came about.

    Pluto will always be an exceptional object, whatever name they might assign it. It is among the largest of the Kuiper Belt Objects, it is presumably the closest, and it is the only one significant enough to be inferred as a discrete entity by examining the orbits of the other planets (AFAIK).

    Once you know that about Pluto, it doesn’t really matter what name you give it. It’s simply an extraordinary object in its own right.

  23. I think that the debate over whether or not to call Pluto a planet illustrates what Feynman said about the difference between knowing the name of something and understanding what it is.

    We now realize that our solar system is a layered system: The inner core has 4 solid planets, in many ways very similar to each other. Then there’s an asteroid belt. Beyond that are 4 gas giants, sharing certain common features. Beyond the gas giants are a large number of rocky objects referred to as “Kuiper Belt Objects”, the largest of which bear some resemblance to the inner planets. These outer objects extend to a considerable distance from the sun.

    Given the differences between the inner planets, the gas giants, and the Kuiper Belt Objects (including Pluto), it would be better to stop talking about a single category known as planets, and instead talk about 3 categories.

    I realize that people don’t want to make such fine distinctions in casual conversation, and that’s fine. But the mere fact that there is so much debate should clue us in that the term “planet” is papering over a wide range of objects, and that there are several distinct categories of objects present. And that should clue us in, once again, on the difference between knowing the name of something and knowing what it is, how it works, and how it came about.

    Pluto will always be an exceptional object, whatever name they might assign it. It is among the largest of the Kuiper Belt Objects, it is presumably the closest, and it is the only one significant enough to be inferred as a discrete entity by examining the orbits of the other planets (AFAIK).

    Once you know that about Pluto, it doesn’t really matter what name you give it. It’s simply an extraordinary object in its own right.

  24. Mother very easily made a (very) cherry jam sandwich using no peanuts, cheese or, errr, xenon?

  25. My kid has a book claiming that Saturn produces more energy than it receives from the Sun. Given Saturn’s distance from the sun, I don’t know how impressive that is, but what are the implications of that? Do the moons get more energy from the planet than they do from the sun? Could this be an energy source for human activity in the outer system?

  26. Tim, IANAA, but if Saturn is giving off more energy than it receives from the sun, it must have some other source for that energy, or it would be a violation of the first law of thermodynamics. I would expect the source of Saturn’s energy output to be fission nuclear activity, but of course, I’m guessing. I’m a biologist, dammit, not an astrophysicist!

  27. Who needs energy anyhow?
    I’m hoping they name a blob out there beyond Pluto, Hammock. All the pensioners who will be cheated out of Social Security could colonize the place.

    Now another plug for Blypton as a name for iffy “planets.”
    Blip-ton
    Blip plus ton
    BLIP
    Blypton sounds spacier.
    Are we grokking yet?
    Ahoy there!

  28. if Saturn is giving off more energy than it receives from the sun, it must have some other source for that energy, or it would be a violation of the first law of thermodynamics.

    I gather from Britannica that it’s not well understood yet, but Saturn radiates twice the energy it receives from the sun. Saturn is too light in mass to still be radiating heat of formation like Jupiter is. The best guess appears to be helium raining out of the hydrogen solution and being slowed by friction.

    As for using this energy, you’d need some meaningful gradient of heat to run a power source. But you can’t passively make something hotter than the heating source, and what Saturn is radiating is still pretty cold.

  29. and it is the only one significant enough to be inferred as a discrete entity by examining the orbits of the other planets (AFAIK).

    Neptune’s orbit appeared irregular to 19th century astronomers because they “misunderestimated” its mass. Pluto is far too small to affect the orbit of a gas giant.

  30. Dear Insignificant Ape-Beings:

    Please cease and dissent referring to our outpost in your star system as “Pluto.” We have been referring to this planetoid as “Yuggoth” long before your kind climbed down from the trees. Comply immediately or we will take legal action (e.g. sacrificed you to Nyralathotep, or having your brain placed in a cylinder).

    Sincerely,
    Yttttttthhhhhddddfffffffkaaaaaaa,
    Administrator, Yuggoth Mining Outpost.

  31. Maybe we should go back to the original meaning of planet, a starlike object that wanders in the sky instead of moving in lockstep with the celestial background. This includes the original set of planets, Mercury, Venus, Mars, Jupiter and Saturn. Include earth if you like, but of course it doesn’t fit the criterion of wandering about the sky. Uranus, discovered later, qualifies because it is just barely visible to the naked eye. Neptune is too faint to see, although you could work it in if you allow binoculars.

    Everything else is an orbiting object, one of various types. Big or not so big, rocky or icy or gaseous, orbiting the sun or another body, etc.

Please to post comments

Comments are closed.