# Is there really a Planet 9 out there in the Kuiper Belt? **URL:** \ **Category:** Factual Questions\ **Created:** [January 29, 2021, 1:49pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771 "2021-01-29T13:49:54Z")\ **Posts on this page:** 20\ **Page:** 5
**Author:** ![Frodo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/frodo/32/302_2.png) [@Frodo](https://boards.straightdope.com/u/Frodo)\ **Post date:** [February 1, 2021, 2:59pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/81 "2021-02-01T14:59:13Z")
We can’t do that, the International Astronomical Union thugs would destroy the servers and salt the earth where they stood. (They’ll probably adopt the hamsters, they are not _complete_ monsters). (Also are the new Discord servers also Hamster-powered?, what happened to the old hamsters? are they in the mod’s houses now? or have they been er… “retired” to the proverbial upstate farm house?, so many questions…) ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [February 1, 2021, 3:03pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/82 "2021-02-01T15:03:51Z")
> [@Frodo](#): > > (Also are the new Discord servers also Hamster-powered?, what happened to the old hamsters? are they in the mod’s houses now? or have they been er… “retired” to the proverbial upstate farm house?, so many questions…) The Discourse servers are powered by much more powerful [capybaras.](https://www.nationalgeographic.com/animals/mammals/c/cabybara-facts/#/capybara.jpg). The hamsters have been “retired” to a commercial snake farm in Florida. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [February 1, 2021, 3:33pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/83 "2021-02-01T15:33:27Z")
> [@Jasmine](#): > > > [@MEBuckner](#): > > > > As far as Pluto being a planet because it has its own moon, meet [Ida](https://en.wikipedia.org/wiki/243_Ida): > > Ida is a chunk of rock with a boulder “trapped” in a gravity field so weak that an athlete could reach escape velocity with simply a standing jump. Ida was just the first asteroid to be definitely known to have a satellite, but it’s hardly the only one. Several hundred are known or suspected. According to Wikipedia, about 2% of all asteroids and 11% of TNOs are thought to have satellites. ---
**Author:** ![MEBuckner](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mebuckner/32/2896_2.png) [@MEBuckner](https://boards.straightdope.com/u/MEBuckner)\ **Post date:** [February 1, 2021, 3:42pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/84 "2021-02-01T15:42:07Z")
> [@Jasmine](#): > > Note to Board: We now have ten planets. If we’re going to accept Ceres and Pluto, there’s pretty much no way we can stop at just ten planets. In addition to Eris (the discovery of which is pretty much responsible for Pluto’s official de-planetization) there’s also Haumea and Makemake–which would bring us to thirteen–and [possibly also](https://en.wikipedia.org/wiki/List_of_possible_dwarf_planets) Gonggong, Quaoar, Sedna, Orcus, and Salacia, not to mention a bunch of things that (so far) are just strings of letters and numbers (“(307261) 2002 MS4”). [Like I said](https://boards.straightdope.com/t/pluto-was-demoted-2-years-ago-shouldnt-a-new-planet-definition-be-proposed/461128/3) 13 years ago (wow, time flies), I think it would be shiny to have dozens and dozens of planets, but I guess the IAU isn’t likely to put me in charge. ---
**Author:** ![MEBuckner](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mebuckner/32/2896_2.png) [@MEBuckner](https://boards.straightdope.com/u/MEBuckner)\ **Post date:** [February 1, 2021, 3:56pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/85 "2021-02-01T15:56:54Z")
Oh, and on the topic of “moons”, and whether having one makes you a planet or not, there’s [something out there way past Neptune](https://en.wikipedia.org/wiki/229762_G%C7%83k%C3%BAn%C7%81%CA%BCh%C3%B2md%C3%ADm%C3%A0) that’s over 600 kilometers across (about 400 miles wide) and has a moon that’s over 100 kilometers across. So, definitely more than just a boulder, although it may not be a fully solid object. Too bad, because I would love to add Gǃkúnǁʼhòmdímà (and its moon, Gǃòʼé ǃHú) to the official planets list. Memorize _that_ ya little bastards! ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [February 1, 2021, 4:30pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/86 "2021-02-01T16:30:49Z")
As I said above, whenever the number of “planets” gets above 10, the astronomical community redefines planet to reduce the number again. Ceres was originally classified as a planet, then reclassified as an asteroid when more were discovered. But there’s no real conceptual reason that it shouldn’t be classified as a planet due to orbit, location, shape (it’s the only asteroid with a spherical shape due to its own gravity), and composition. It has much more in common with the rocky planets than it does with Pluto. I don’t mind calling Pluto and other Kuiper Belt objects something else due to composition and location, but a highly contrived definition that puts Ceres in the same group IMO is ridiculous. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [February 1, 2021, 4:38pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/87 "2021-02-01T16:38:35Z")
Never mind memorize. I’d love to hear one of you _uitlanders_ just try and _[pronounce](https://upload.wikimedia.org/wikipedia/en/3/3a/G%C7%83kun%C7%81%27homdima.ogg)_ [them](https://upload.wikimedia.org/wikipedia/en/7/7f/G%C7%83o%27e_%C7%83Hu.ogg) with the words in front of you. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [February 1, 2021, 5:52pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/88 "2021-02-01T17:52:50Z")
How about we group some of the planets based on for how long they were considered one of “The Planets of the Solar system”? We can call the group the neo-classical planets and teach those in school. And then the Astronomers can make up and rearrange whatever classifications they feel are useful like rockballs, iceballs, gasballs and blue balls, without it influencing what Joe Schmo remembers from school. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [February 1, 2021, 5:58pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/89 "2021-02-01T17:58:22Z")
> [@naita](#): > > How about we group some of the planets based on for how long they were considered one of “The Planets of the Solar system”? We can call the group the neo-classical planets and teach those in school. The Earth wasn’t considered to be a planet for thousands of years. It’s only been generally recognized as a planet within the past 400 years, a much shorter time than the other “classical” planets. ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [February 1, 2021, 6:04pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/90 "2021-02-01T18:04:05Z")
> [@naita](#): > > How about we group some of the planets based on for how long they were considered one of “The Planets of the Solar system”? As always, there’s a Wikipedia article for that: > **[List of former planets](https://en.wikipedia.org/wiki/List_of_former_planets)** > > This is a list of astronomical objects formerly widely considered planets under any of the various definitions of this word in the history of astronomy. As the definition of planet has evolved, the de facto and de jure definitions of planet have changed over the millennia. As of 2022, there are 8 official planets in the Solar System by the IAU, and many more exoplanets. Several objects formerly considered exoplanets have been found actually to be stars or brown dwarfs. > Throughout antiquity, se... ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [February 1, 2021, 6:43pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/91 "2021-02-01T18:43:49Z")
And the Sun and the Moon were considered planets, making 7 “classical” planets ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [February 1, 2021, 8:03pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/92 "2021-02-01T20:03:16Z")
> [@Colibri](#): > > The Earth wasn’t considered to be a planet for thousands of years. It’s only been generally recognized as a planet within the past 400 years, a much shorter time than the other “classical” planets. > [@Andy\_L](#): > > And the Sun and the Moon were considered planets, making 7 “classical” planets And that’s why I suggested calling them “neo-classical”! I’m sure there won’t be any other issues and everyone will agree to this compromise. 🙂 ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [February 1, 2021, 8:35pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/93 "2021-02-01T20:35:26Z")
Really, the only reason to be concerned about the definition of a planet is to make a convenient list to recite. The eight bodies currently recognized as planets fall into two very different groups, while objects called dwarf planets, asteroids, satellites, and other bodies are more similar to one or the other of the two groups than the groups are to each other. Calling an object a planet doesn’t really tell us anything unique about it. ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [February 1, 2021, 9:09pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/94 "2021-02-01T21:09:38Z")
> [@Colibri](#): > > Really, the only reason to be concerned about the definition of a planet is to make a convenient list to recite. The eight bodies currently recognized as planets fall into two very different groups, while objects called dwarf planets, asteroids, satellites, and other bodies are more similar to one or the other of the two groups than the groups are to each other. I guess much depends on what one considers to be the most important characteristics to establish “commonality”. I find a persuasive aspect of commonality to be the fact that the eight recognized planets orbit the sun close to the same orbital plane, in orbits that are nearly circular, all being a consequence of having condensed from the same protoplanetary disk. They are also large enough to be fairly easily visible from Earth; all except Neptune in fact at times visible with the naked eye, and Neptune visible with the kind of telescope easily accessible to the amateur backyard astronomer. I’ve always thought of Pluto as the odd man out, even before its official demotion, because of its eccentric orbit that was also way out of the ecliptic shared by all the other planets. I must say I was very surprised at the fascinating results of the New Horizons mission. I had thought of Pluto as an uninteresting piece of ice in the fringes of the solar system, and it turns out to be a very interesting and geologically active place (albeit a bit chilly – the kind of place where you’d need a quality overcoat and a good pair of mittens!). 😉 ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 1, 2021, 9:15pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/95 "2021-02-01T21:15:20Z")
@wolfpup, that’s a reasonable standard, but note that it would also include Ceres and (arguably) Luna. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [February 1, 2021, 9:16pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/96 "2021-02-01T21:16:15Z")
> [@wolfpup](#): > > I guess much depends on what one considers to be the most important characteristics to establish “commonality”. I find a persuasive aspect of commonality to be the fact that the eight recognized planets orbit the sun close to the same orbital plane, in orbits that are nearly circular, all being a consequence of having condensed from the same protoplanetary disk. That’s a reasonable definition, but IMO the exclusion of Ceres is arbitrary. Rather than an artificial lower limit on size, it would be sensible to have one based on physical characteristics such as shape. Admittedly there’s a huge gap in size between Mercury and Ceres, but there’s a pretty big gap between Neptune and Earth too. ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [February 1, 2021, 9:31pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/97 "2021-02-01T21:31:13Z")
That’s where the “clearing the orbit” test kicks in, though. There have been three different measurements for how to define “clearing the orbit”, and all of them have a substantial gap between Mars, which has the lowest rating, and Ceres, the next one down. The wiki article on it describes it as being “orders of magnitude” different between the eight planets and Ceres, Pluto and the rest. > **[Clearing the neighbourhood](https://en.wikipedia.org/wiki/Clearing_the_neighbourhood)** > > Pages for logged out editors learn more > > "Clearing the neighbourhood" (or dynamical dominance) around a celestial body's orbit describes the body becoming gravitationally dominant such that there are no other bodies of comparable size other than its natural satellites or those otherwise under its gravitational influence. > "Clearing the neighbourhood" is one of three necessary criteria for a celestial body to be considered a planet in the Solar System, according to the definition adopted ... ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [February 1, 2021, 9:33pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/98 "2021-02-01T21:33:35Z")
> [@Chronos](#): > > @wolfpup, that’s a reasonable standard, but note that it would also include Ceres and (arguably) Luna. Fair. I would definitely argue against Luna as it does not (independently) orbit the sun. Ceres is pretty arbitrary, as @Colibri said. My view would be no, because it’s a particularly egregious case of having failed to “clear its orbital path”. Essentially Ceres is a very large rock among a whole orbital ring of other rocks. But I would certainly acknowledge that these sorts of arguments begin to illustrate why many of these definitions are pretty arbitrary. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [February 1, 2021, 9:47pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/99 "2021-02-01T21:47:59Z")
> [@wolfpup](#): > > I guess much depends on what one considers to be the most important characteristics to establish “commonality”. I find a persuasive aspect of commonality to be the fact that the eight recognized planets orbit the sun close to the same orbital plane, in orbits that are nearly circular, all being a consequence of having condensed from the same protoplanetary disk. They are also large enough to be fairly easily visible from Earth; all except Neptune in fact at times visible with the naked eye, and Neptune visible with the kind of telescope easily accessible to the amateur backyard astronomer. By this thinking, the hypothesized Planet 9 will not be a planet, even though it’s way bigger than Earth. It doesn’t check any of the boxes except having formed in the same protoplanetary disk. BTW, the subject line of this thread is mistaken. Planet 9 is not in the Kuiper Belt. It’s _way past_ the Kuiper Belt. And the last time I checked, they’d changed their guess as to its mass. Now they think it’s only about 5 Earth masses, rather than 10. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 1, 2021, 11:44pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/100 "2021-02-01T23:44:05Z")
I’ve never been a fan of the “cleared its orbit” criterion, because Earth fails that one, too. Luna is an awfully big hunk of rock to be sharing our orbit with. [Previous page](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771.md?page=4) [Next page](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771.md?page=6)