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Recent news seem to suggest that astronomers are arguing about whether Pluto should become a planet again.

However, I cannot find an official source for this. Is this actually true?

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    $\begingroup$ There is only one way to end this conflict once and for all... destroy Pluto $\endgroup$ Oct 5, 2014 at 15:13
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    $\begingroup$ @Tom I doubt the New Horizons probe has an explosive device on board. :-) $\endgroup$
    – HDE 226868
    Oct 5, 2014 at 15:15
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    $\begingroup$ @Omen I just emailed what-if, I hope this will be answered. $\endgroup$ Oct 5, 2014 at 15:29
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    $\begingroup$ @Tom, alas, if we destroy Pluto, academics will start arguing about what Pluto was. $\endgroup$
    – msw
    Oct 6, 2014 at 1:01
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    $\begingroup$ Keep in mind that the debate is about the meaning of the English word "planet". Pluto itself quite literally couldn't care less. No perfectly consistent classification is possible anyway; is Mercury really more similar to Jupiter than to Ceres? $\endgroup$ Oct 6, 2014 at 18:35

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Yes, Pluto is still a dwarf planet. According to the IAU website, it still fits the criteria for a dwarf planet, fails to meet the criteria for a planet, and still carries the "dwarf planet" label, whatever its future status may be. I'm sorry I can't provide a longer or more detailed answer, but this is really a yes-or-no question.

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  • $\begingroup$ Good answer, the media certainly plays on any little deviation, as they did with the debate quoted in my answer. $\endgroup$
    – user2449
    Oct 5, 2014 at 15:26
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    $\begingroup$ @Omen Thanks. My answer is boring, but I couldn't find much else. I decided to avoid Wikipedia for this one. $\endgroup$
    – HDE 226868
    Oct 5, 2014 at 15:28
  • $\begingroup$ It was just by chance I was reading about the debate in my answer when the question appeared - the rest of the reports are just the media. $\endgroup$
    – user2449
    Oct 5, 2014 at 15:30
  • $\begingroup$ Your answer is doing better than mine..;) $\endgroup$
    – user2449
    Oct 5, 2014 at 15:40
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    $\begingroup$ @Omen We'll see. Low views for the question so far. . . But good upvotes for the question itself. $\endgroup$
    – HDE 226868
    Oct 5, 2014 at 15:41
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A lot of the push to have Pluto reinstated as the 9th planet is coming from Harvard, from their press release Is Pluto a Planet? The Votes Are In (Released September, 2014), they state the following outcomes from a debate:

Science historian Dr. Owen Gingerich, who chaired the IAU planet definition committee, presented the historical viewpoint. Dr. Gareth Williams, associate director of the Minor Planet Center, presented the IAU's viewpoint. And Dr. Dimitar Sasselov, director of the Harvard Origins of Life Initiative, presented the exoplanet scientist's viewpoint.

Gingerich argued that "a planet is a culturally defined word that changes over time," and that Pluto is a planet. Williams defended the IAU definition, which declares that Pluto is not a planet. And Sasselov defined a planet as "the smallest spherical lump of matter that formed around stars or stellar remnants," which means Pluto is a planet.

We will have a better understanding of Pluto, hence its classification when NASA's Horizons mission reaches it. But, at this stage, Pluto is still classified as a dwarf planet.

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    $\begingroup$ It would have been awesome to be at this debate $\endgroup$
    – user2449
    Oct 5, 2014 at 15:23
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    $\begingroup$ For a second, I saw "Gingrich" instead of "Gingerich" and got really worried. $\endgroup$
    – HDE 226868
    Oct 5, 2014 at 15:24
  • $\begingroup$ You and me both! $\endgroup$
    – user2449
    Oct 5, 2014 at 15:24
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    $\begingroup$ "(T)he smallest spherical lump of matter that formed around stars or stellar remnants" would raise the number to higher than nine for our solar system. Pluto could then be the 10th planet since Ceres was called a planet more than a century before Pluto, and Ceres still fits the quoted definition. At least Eris, Makemake and Haumea would also need to be added, giving us 13 "planets" so far, with more likely to be found. (It's less clear about Charon.) We're getting crowded. $\endgroup$ Oct 6, 2014 at 5:23
  • $\begingroup$ @user2338816 I agree that Charon doesn't even fit the dwarf planet definition, partly because it doesn't hold gravitational dominance over its surroundings. $\endgroup$
    – HDE 226868
    Oct 7, 2014 at 1:41
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Pluto will continue to be exactly Pluto no matter how we choose to categorize it. Fretting about the "proper" category is the tyranny of the discontinuous mind.

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    $\begingroup$ In that case, we're all tyrants. Richard Dawkins can be an atheist's best friend, but at the moment he's irrelevant. It's a deep answer, though. Philosophical. $\endgroup$
    – HDE 226868
    Oct 6, 2014 at 1:07
  • $\begingroup$ I cited Dawkins because I know I cribbed the phrase from somewhere (Dennet, Hofstadter, maybe?) but didn't look real hard for the source. The Dawkins article was more political than I wanted, but it did cover the concept well. And yes, we are all categorizing "tyrants" except those who have stars on our bellies; even Dr. Seuss gets philosophical at at times. $\endgroup$
    – msw
    Oct 6, 2014 at 1:15
  • $\begingroup$ Note that Dawkins used the phrase earlier in "The Ancestor's Tale," in a much less political context. $\endgroup$
    – rob
    Jan 21 at 19:01
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The 3rd requirement for a celestial object to be a planet is that it has to "clear its neighborhood" which means it has to be gravitationally dominant. Pluto has not enough mass to interact with other object in its orbit(consuming them or swinging them away) and it is only 0.07 times the mass of the other objects in its orbit. Earth is 1.7 million times the mass of other objects in its orbit.

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Currently, Pluto is very much a dwarf planet. I don't think Pluto will ever be reinstated as a planet again . . . On the the pro-planet side, Pluto has five moons, which can possibly qualify it as a planet. On the no-planet side, Pluto has a mass of 1.30900 × 10^22 kilograms, which is much lower than the currently smallest planet, Mercury, which weighs 3.285 x 10^23 kilograms. Also, the diameter of Mercury is 4,879.4 km across, while Pluto’s diameter is 2,360 km across. Big difference. Really. I'm pretty sure Pluto won't be called a planet again, but I can't be certain.

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  • $\begingroup$ One argument I dislike is the one with the moons. It's a problem for Mercury and Venus, and even Earth has no more moons than many an asteroid or dwarf planet. $\endgroup$ Jun 22, 2023 at 23:08
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Moons Are Planets: Scientific Usefulness Versus Cultural Teleology in the Taxonomy of Planetary Science is a 2021 paper that outlines a thesis that:

  • Until the 20th century, the term 'planet' always included the Moon.
  • That the fields of planetary science -- oceans, atmospheres, (cryo-) volcanism, complex ice and silicate chemistry -- do not care about orbital structure, and that these are found on larger satellites, Pluto and Ceres.

Venn diagram of planets and their shared properties

  • That the IAU was unduly influenced by dynamicists, who typically care very little about the properties of the planet beyond its mass and orbit, and that the vote should not have taken place.
  • That a definition of planet as "big enough for gravitational compression, not so big it's undergoing fusion" encompasses the domain in which complex chemical behaviours are uniquely found within the universe, and that such a definition has useful descriptive value, unlike the IAU definition.
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    $\begingroup$ Dissident view of some astronomers doesn’t change the official decision of the IAU… $\endgroup$ Jun 22, 2023 at 2:53
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In the end, astronomers can call anything they want a "planet". However, some form of distinction should be made between objects that clear their neighborhoods and those that do not. Clearing the neighborhood is a major structural feature of our Solar System, for it leads to the small bodies that make up most of the Solar System's population being largely confined to specific belts and zones.

Earth is one of a select group objects responsible for that, and so is Mercury. Pluto and Ceres cannot really be their equals no matter what words we choose as labels.

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Yes, Pluto is a dwarf planet, along with Ceres and Eris which are in the Solar System. It was classified a dwarf planet in 2006 or 2007. Sorry for my inaccurate answer.

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Only the International Astronomical Union (IAU) has the mandate to decide what is or is not a planet or a dwarf planet. Or, as Keith Thompson rightfully pointed out, about what the word “planet” and the expression “dwarf planet” mean in English.

The IAU holds a General Assembly every three years. The next one is schedule for August 2024 (in Cape Town, South Africa). I doubt the issue of Pluto will be at the agenda, despite popular media claims and complaints by multiple professional astronomers.

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When Piazzi discovered 1Ceres in 1801, it was designated as a planet, and so was several more asteroids as they were discovered in the next few years until they figured out that they were all very small objects in a belt. Pluto was not the first to be demoted. Once others like Pluto was discovered and they realized that it was just one of many, even the largest of many, it was duly demoted.

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