# 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:** 4
**Author:** ![Lucas\_Jackson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lucas_jackson/32/303_2.png) [@Lucas\_Jackson](https://boards.straightdope.com/u/Lucas_Jackson)\ **Post date:** [January 30, 2021, 7:24pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/61 "2021-01-30T19:24:01Z")
> [@naita](#): > > but then I looked for a more qualified opinion and discovered that Phil Plait, my go to qualified opinion on astronomy, is in fact putting his (rhetorical) money on Planet 9. I’m not an astronomer so I ask this in ignorance, how is it that we can detect planets around other stars (if my understanding is correct we’ve discovered about 4,000 so far) at great distances but not one so much (relatively) closer? ---
**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:** [January 30, 2021, 7:51pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/62 "2021-01-30T19:51:32Z")
We can detect planets that are close to stars. We can’t (or only with great difficulty) detect planets far away from stars. All exoplanet discoveries are based, in some way or another, on watching the parent star, not on directly watching the planet itself. ---
**Author:** ![Jackknifed\_Juggernaut](https://avatars.discourse-cdn.com/v4/letter/j/9de053/32.png) [@Jackknifed\_Juggernaut](https://boards.straightdope.com/u/Jackknifed_Juggernaut)\ **Post date:** [January 30, 2021, 7:51pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/63 "2021-01-30T19:51:59Z")
If I understand correctly, the way we detect planets of stars that are very far away is by monitoring how much of their light coming towards us is blocked by a planet passing in front. This obviously wouldn’t be possible with Planet 9. That said, it sure does seem odd that bodies thousands of light years away are easier to detect than something much much closer. ---
**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:** [January 30, 2021, 8:52pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/64 "2021-01-30T20:52:52Z")
> [@Lucas\_Jackson](#): > > I’m not an astronomer so I ask this in ignorance, how is it that we can detect planets around other stars (if my understanding is correct we’ve discovered about 4,000 so far) at great distances but not one so much (relatively) closer? What are you talking about? We’ve detected lots and lots of planets and smaller bodies in this system. 😉 And to add to Chronos’ point, there’s a wide range of planets we’ve discovered around other stars, but many of those systems are bound to have lots of tiny bodies whose influence on their star are to insignificant to be noticed above the noise and the influence of their larger siblings. ---
**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:** [January 30, 2021, 8:56pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/65 "2021-01-30T20:56:10Z")
That’s one method. Another is to analyze the doppler shift of the star and figure out what kind of planets are needed to explain its specific wobble. ---
**Author:** ![erysichthon](https://avatars.discourse-cdn.com/v4/letter/e/d07c76/32.png) [@erysichthon](https://boards.straightdope.com/u/erysichthon)\ **Post date:** [January 30, 2021, 9:45pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/66 "2021-01-30T21:45:03Z")
> [@Cervaise](#): > > Nobody. But the site owner wants clicks. It wouldn’t be the first link farm on the web. I recently stumbled onto a “news” site with a double-translated version of a Los Angeles Times article. The original source wasn’t named, but I recognized the article despite its peculiar phrasing and word choices. I’m guessing there is a lot of that going on; it’s an easy way to generate web content without paying for it. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [January 30, 2021, 10:24pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/67 "2021-01-30T22:24:12Z")
The “weird news” tangent has this spin-off page: > [@Fear is like our planet. That is what Super Earth scientists say](https://boards.straightdope.com/t/fear-is-like-our-planet-that-is-what-super-earth-scientists-say/931841): > > This site seems to take English web articles and translate them into bad English? All the articles are winners, but here is the source of thread title. [https://presstories.com/2021/01/27/this-planet-is-1000-crore-years-old-it-is-super-earth-it-seems-to-be-alive/](https://presstories.com/2021/01/27/this-planet-is-1000-crore-years-old-it-is-super-earth-it-seems-to-be-alive/) ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [January 31, 2021, 1:21pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/68 "2021-01-31T13:21:53Z")
> [@SCAdian](#): > > A prairie dog is not a dog. Small dogs and large dogs are dogs. > A sea lion is not a lion. Small lions and large lions are lions. > A [size] [object] is an [object] I hope you’re kidding with this silly tilting at windmills, but if you’re not … A [size=adjective] [object] is an [object] A [sub-class=noun] [object] is a [subclass object] The compound term “dwarf planet” is a noun describing a class of objects with certain traits. Traits that are different from the traits of a “planet”. The traits are disjoint enough that no planet has _all_ the traits of a dwarf planet, and no dwarf planet has _all_ the traits of a planet. The compound term “dwarf planet” is not synonymous with the qualitative description “smallish planet”. In further news, we may say that “Texas is flat”. That doesn’t mean the Earth is flat. One hopes you agree. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [January 31, 2021, 2:28pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/69 "2021-01-31T14:28:03Z")
A German Shepherd is not a dog. A German Shepherd Dog is a dog. > **[German Shepherd Dog Dog Breed Information](https://www.akc.org/dog-breeds/german-shepherd-dog/)** > > Right breed for you? German Shepherd Dog information including personality, history, grooming, pictures, videos, and the AKC breed standard. ---
**Author:** ![Borborygmi](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/borborygmi/32/217_2.png) [@Borborygmi](https://boards.straightdope.com/u/Borborygmi)\ **Post date:** [January 31, 2021, 7:57pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/70 "2021-01-31T19:57:24Z")
> [@Darren\_Garrison](#): > > A German Shepherd is not a dog. A German Shepherd Dog is a dog. This why I support classing dogs as oddballs and meatballs. ---
**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:** [January 31, 2021, 8:15pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/71 "2021-01-31T20:15:48Z")
> [@Colibri](#): > > Cary Douglas’s/muhammad’s/Wayne Ma’s [other articles on the site](https://presstories.com/author/muhammad/) are similarly garbled. > > I would wonder why [The Press Stories](https://presstories.com/about-us/) websites allows this, but it seems like the owner is also not a native English speaker. Apparently so. Their “editorial policy” section includes information for aspiring writers on how to write and submit an article which includes this wonderful statement: “When an article is accepted, we will intimidate you with our decision.” 😃 ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [January 31, 2021, 8:20pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/72 "2021-01-31T20:20:23Z")
> [@wolfpup](#): > > “When an article is accepted, we will intimidate you with our decision.” 😃 Great find. ---
**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:** [January 31, 2021, 8:30pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/73 "2021-01-31T20:30:33Z")
A website published by bots, for bots! ---
**Author:** ![eburacum\_45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum_45/32/3385_2.png) [@eburacum\_45](https://boards.straightdope.com/u/eburacum_45)\ **Post date:** [January 31, 2021, 8:55pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/74 "2021-01-31T20:55:40Z")
> [@Jackknifed\_Juggernaut](#): > > If the list is correct, the Earth is the densest of all of them. Mercury is a close 2nd. The situation is a bit more complicated than that. Mercury is in fact made of denser material than Earth, but Earth is more compressed by its own weight. From Wikipedia > [@](#): > > Mercury’s density is the second highest in the Solar System at 5.427 g/cm3, only slightly less than Earth’s density of 5.515 g/cm3.[[3]](https://en.wikipedia.org/wiki/Mercury_(planet)#cite_note-fact-3) If the effect of [gravitational compression](https://en.wikipedia.org/wiki/Gravitational_compression) were to be factored out from both planets, the materials of which Mercury is made would be denser than those of Earth, with an uncompressed density of 5.3 g/cm3 versus Earth’s 4.4 g/cm3.[[25]](https://en.wikipedia.org/wiki/Mercury_(planet)#cite_note-27) ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [January 31, 2021, 9:33pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/75 "2021-01-31T21:33:14Z")
> [@eburacum\_45](#): > > … Earth’s density of 5.515 g/cm3. … with an uncompressed density of … Earth’s 4.4 g/cm3. Cool find! So Earth gravity is adding 25% to Earth’s density (4.4 → 5.5). To my non-expert intuition that’s a gigantically big multiplier when you consider how incompressible most of Earth’s materials are. And that some of the stiffest densest stuff is where the pressures are greatest. Which raises an interesting thought … Earth’s gravity is highest at the surface and decreases as you go down towards the center whereat gravity is zero. The pressure goes up monotonically as you descend because there’s an ever-increasing pile of stuff above you pressing down. Given the various densities of the stuff, from atmosphere to ocean to crustal rock to mantle rock to core materials, the pressure should increase at different rates at different depths as those two factors play off against each other. So how does the pressure vary by depth? Here’s what I found after just a bit of reading: **[This wiki](https://en.wikipedia.org/wiki/Structure_of_Earth)** has some informative graphs on density and gravity by depth, but not one of pressure. Here’s a **[pressure graph](https://www.researchgate.net/figure/The-pressure-at-different-depths-in-the-Earths-interior_fig12_228377528)**, but with the X-axis reversed vs the wiki graphs. There’s a distinct bump in the rate of pressure increase as you transition from the mantle into the outer core. And the declining gravity isn’t really a factor until you’re very close to the center. Cool! Still surprised it’s worth 25% though. ---
**Author:** ![eburacum\_45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum_45/32/3385_2.png) [@eburacum\_45](https://boards.straightdope.com/u/eburacum_45)\ **Post date:** [January 31, 2021, 10:23pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/76 "2021-01-31T22:23:13Z")
Personally I would not be surprised if there were half a dozen large planets in the Oort cloud, Earth-sized or bigger. We aren’t going to see them because they are far away, small, cold, and poorly-lit by the Sun. ---
**Author:** ![Jasmine](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jasmine/32/2964_2.png) [@Jasmine](https://boards.straightdope.com/u/Jasmine)\ **Post date:** [February 1, 2021, 2:10pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/77 "2021-02-01T14:10:39Z")
That is acceptable! 🙂 Note to Board: We now have ten planets. ---
**Author:** ![Jasmine](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jasmine/32/2964_2.png) [@Jasmine](https://boards.straightdope.com/u/Jasmine)\ **Post date:** [February 1, 2021, 2:13pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/78 "2021-02-01T14:13:12Z")
> [@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. ---
**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, 2:25pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/79 "2021-02-01T14:25:52Z")
The bigger a solid planet is the more dense it is likely to be because of gravitational compression, too. ---
**Author:** ![Frazzled](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/frazzled/32/3368_2.png) [@Frazzled](https://boards.straightdope.com/u/Frazzled)\ **Post date:** [February 1, 2021, 2:38pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/80 "2021-02-01T14:38:26Z")
But what if all of this discussion about Pluto being a planet is moot? Some researchers think Pluto might be a comet! > If being downgraded from planet to dwarf planet back in 2006 was one identity crisis for Pluto, here’s another: Scientists now say the ninth rock from the sun could be a sort of giant comet, having formed when a billion or so comets clumped together in the [solar system’s early days](https://www.nbcnews.com/mach/science/newfound-asteroids-may-help-explain-our-solar-system-s-origins-ncna789526). From: [New theory suggests Pluto may be a giant comet](https://www.nbcnews.com/mach/science/pluto-s-life-story-may-have-begun-billion-comets-ncna879256) [Previous page](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771.md?page=3) [Next page](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771.md?page=5)