Pluto Reinstated?

Hubble's View of Pluto and Charon
Hubble's View of Pluto and Charon

Will Pluto be reissued its former status as a full-fledged planet? While it won’t necessarily be a topic of debate at next week’s meeting of the International Astronomical Union – the group in charge of, amongst other things, the official naming of all things extraterrestrial and thus the group responsible for voting Pluto off the planetary island three years ago – it may be the end result of new discoveries in the years ahead…the kinds of discoveries that make the most recent definitions of what signifies a “planet” hard to clarify.

Pluto, discovered in 1930 by Illinois native Clyde Tombaugh, was classified as the ninth planet until the IAU relegated it to dwarf planet status in 2006 due to some new “requirements” of planethood – notably, having enough gravitational influence to clear the path within one’s own orbit. (Illinois, by the way, officially claimed Pluto’s downgraded status as “unfair” and declared March 13, 2009 as “Pluto Day”.) This change was met with mixed reaction by the scientific community and concerned folks everywhere (at least those concerned about such things) and is still hotly debated in some circles.

At least in circles that debate such things hotly.

Anyway, some scientists – namely, Mark Sykes of Tucson’s Planetary Science Institute – think that the results of missions like NASA’s New Horizons spacecraft currently en route to Pluto will challenge the revised qualifications of planethood with their findings, perhaps demanding a re-evaluation. Sykes and others believe if an object directly orbiting a star is big enough for its own gravity to force it into a spherical shape, it should be a planet, regardless of how well it keeps its orbital room clean. Some say that Earth would have a hard time clearing the space around its orbit were it at Pluto’s distance from the sun due to the sheer length of time it takes to make the round trip. (248 years, to be exact.)

Of course, this definition would then have to promote some other worlds to official planetary status too…such as Ceres, an exceptionally large asteroid circling the sun between Mars and Jupiter, as well as many yet-to-be discovered bodies within the Kuiper Belt region even further out than Pluto. But, according to Sykes, the status of “planet” should be given according to our expanding scientific knowledge and not kept out-of-reach purely out of tradition.

“We are shaking off the last vestiges of the mythological view of planets as special objects in the sky – and the idea that there has to be a small number of them because they’re special.” – Mark Sykes, Planetary Science Institute, Tucson, AZ.

Regardless of its classification in science journals and textbooks, the New Horizons mission will be undoubtedly reveal fascinating information about Pluto and its moon, Charon. Even with powerful instruments like the Hubble Space Telescope, at 2.6 billion miles away they only appear as blurry points of light from here. Launched in January 2006, New Horizons will arrive at Pluto in 2015, do a flyby, and then soar into the Kuiper Belt and eventually out of the solar system entirely. The data it sends back will be the most detailed information we will have ever had about this most debated-over member of our solar system.

Planet or not, the results will definitely be exciting.

Read the article on this from

Read more about Pluto and Charon.



  1. Bill says:

    I’m firmly in the non-planet camp. If Pluto’s a planet, then so is Eris and Ceres and Quaoar and Varuna and Makemake and on and on. This is not a demotion, it’s just a new class of body. Insisting that Pluto is a planet is like insisting that a cat is a dog, just because for long time all we knew about were dogs. So there. 🙂


  2. Bill says:

    Excellent post, by the way.


  3. And I’m firmly in the planet camp. So what if that means Ceres, Haumea, Makemake, and Eris also join the planet camp? Why do some feel a need to artificially keep the number of planets small? We don’t limit the number of elements in the Periodic Table because there are too many to memorize. Memorization is not that important anyway; what is more important is understanding concepts such as the key characteristics of each subclass of planet.

    Pluto did not stop being a planet because 424 astronomers made a controversial decision and adopted a vague, unusable planet definition. The requirement that an object “clear its orbit” was concocted specifically to exclude Pluto and keep the number of planets in our solar system low. The IAU definition makes no sense in stating that dwarf planets are not planets at all, a departure from the use of the term “dwarf” in astronomy, where dwarf stars are still stars, and dwarf galaxies are still galaxies. Also, the IAU definition classifies objects solely by where they are while ignoring what they are. If Earth were in Pluto’s orbit, according to this definition, it would not be a planet either. A definition that takes the same object and makes it a planet in one location and not a planet in another location is essentially useless.

    The IAU should take responsibility for the highly flawed definition adopted by only four percent of its members, most of whom are not planetary scientists, in 2006. However, the IAU should not be viewed as the sole authority on the definition of planet. Many planetary scientists do not belong to the IAU. Should they not have a say in this matter? Something does not become fact simply because a tiny group that calls itself an authority says so. It is significant that hundreds of planetary scientists led by New Horizons Principal Investgator Alan Stern immediately signed a formal petition opposing the IAU definition.

    There are other venues through which a planet definition can be determined, such as last year’s Great Planet Debate at the Johns Hopkins University Applied Physics Lab. Audio and video proceedings from this far more balanced conference, which I was fortunate to attend, can be found online.


    1. J. Major says:

      I’m not quite sure myself of the politics behind the new designation of Pluto, but I am in favor of keeping it as a planet. For reasons of its shape, and the fact that it independently orbits the sun (unlike a moon), and that, historically, the word “planet” is from the ancient Greek word for “traveler” and, if nothing else, little Pluto sure does a whole lot of traveling in the far reaches of our solar system.

      I have no problems with the steady growth of planets on the books. Perhaps I’m wrong, but wasn’t Ceres once considered a planet too? We have no idea of the exact amount of members in our solar system, it seems shortsighted to create a self-fulfilling yet rather arbitrary cap to how we classify things. For a metaphor to rebut Bill’s, if you learn today your father had a brother you never knew of, does it make him any less your uncle?

      I agree that the decision to change Pluto’s classification should probably have undergone some wider polling than it did. If only that it did happen to have such a special status as a planet. I doubt anyone would have minded as much if some planets were added to the list either.

      Even if it would screw up My Very Eager Mother Just Served Us Nine Pies.


      1. Justin says:

        From J. Major – “We have no idea of the exact amount of members in our solar system, it seems shortsighted to create a self-fulfilling yet rather arbitrary cap to how we classify things.”

        You are right that it is all arbitrary. However, that is what classifying is.

        Classify – arrange or organize by certain attributes or traits in common; a kind or category.

        Classification is often subject to change in science. The Pandas were once classified as bears. later as raccoons and now as one panda species in each. This is no different

        I think the general misunderstanding is that people think this reclassification is somehow derogatory towards Pluto. But scientific classification is not really an evaluation of overall merit. Usually when reclassification happens, it is because newer information has been obtained since the original classification, and the new classification makes them more descriptive. The boundaries are generally arbitrary, but boundaries need to be chosen to classify. The IAU simply voted on how to designate these new descriptions. Classifying pluto and the like bodies as planets was one choice and classifying them as dwarf planets was another. Neither is absolutely better than the other. I imagine just as many people would have been upset about “planet proliferation” and the “sanctity of the planet name” if they had gone the other way. But they didn’t so we have upset people in the “Pluto and his buddies will not be second class citizens” type of argument.

        It is interesting what people will latch on to. Its like arguing whether your car is a small or mid-sized SUV. Seem ridiculous? Search for people who are upset that their cars were not classified as “clunkers” for the cash for clunkers program. Yes the clunker definition line was arbitrary, but there had to be a line. And, there goal was to get cars sold by using a budget to subsidize the replacement of those arbitrarily defined class of vehicles. Whether or not you agree with the politics of it, the program succeeded in meeting its defined goal, angry dissenters with cars just outside the definition notwithstanding.

        I love you pluto! Dwarf or no!


        1. J. Major says:

          I’m definitely on the side of “planet proliferation”. If i see a globe of decent…globeness….and orbit a star, I call “planet”. If it’s little then it’s a small planet. Pluto’s a small planet. So is Mercury and Mars and even Earth and Venus, depending on your point of view. But still all planets. And if they wanted to call Ceres a planet, well, why not. It was once classified as such, so someone had to agree at one time.

          But overall it’s silly to argue such points, as they get one nowhere. Perhaps equally as silly as spending time reclassifying. Pluto IS, regardless of the words we use to denote it. And that’s what’s great about it.


      2. Justin says:

        Great blog by the way. I just spent way too much time reading it!


        1. J. Major says:


          Sometimes I think I spend way too much time writing it. 😉


  4. Bill says:

    I should clarify that my issue is not necessarily with increasing the number of planets, only with the irreconcilable inconsistency of designating Pluto a planet, but not the other small icy bodies.


    1. J. Major says:

      Make ’em all planets, I say. Small and icy notwithstanding.


  5. Terry says:

    Jay – great mnemonic – but I agree with with the idea behind the IAU guidelines:
    1. Round by it’s own gravity
    2. Able to clean it’s own room
    3. Not orbiting something else.

    Hey, Pluto-Charon and the two other moons are orbiting a center of gravity in-between the four.

    The politics of this is STUPID. The largest examples of a large number of similar objects (Ceres and asteroids) (or Pluto et all and KBOs) should not be elevated out of that group because of “history” or 2 million flaming emails from 3rd graders.


    1. J. Major says:

      I don’t see what the big deal is about clearing up one’s orbit. Couldn’t two planets potentially share an orbit? Maybe not in our solar system, but in another one? If we ever discover a situation like that what will we call them?


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