# 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:** 7
**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 2, 2021, 10:46pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/121 "2021-02-02T22:46:31Z")
Except that doesn’t apply to all members of the family, particularly Ceres, which is considered an interloper in the Gefion family. ---
**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:** [February 2, 2021, 11:44pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/122 "2021-02-02T23:44:10Z")
Not relevant. To use an earlier analogy, a poodle still was a poodle even of you put it through a wood chipper. And that isn’t changed if a Saint Benard comes in and sits in the bits. Or What happens to a body millions of years after the proto-panetary disc disperses/is used up ain’t got nothing to do with how objects formed in that disc. ---
**Author:** ![RTFirefly](https://avatars.discourse-cdn.com/v4/letter/r/c77e96/32.png) [@RTFirefly](https://boards.straightdope.com/u/RTFirefly)\ **Post date:** [February 3, 2021, 12:11am UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/123 "2021-02-03T00:11:43Z")
> [@Colibri](#): > > As we have learned more about the solar system, the definition of planet has been tweaked to keep the their number between 5 and 9. Once we find more than 9 objects (like asteroids or Kuiper Belt objects) that fit the previous definition of planet the definition gets changed to keep the number small. It isn’t that a tenth object gets found. In both instances - asteroids and KBOs - it’s been that there’s been no good place to stop after that. If Pluto or Ceres is a planet, then wherever you draw the line between planet and non-planet in order to not have _dozens_ of planets is arbitrary. If that wasn’t the case, they’d still be 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 3, 2021, 12:23am UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/124 "2021-02-03T00:23:40Z")
> [@Darren\_Garrison](#): > > What happens to a body millions of years after the proto-panetary disc disperses/is used up ain’t got nothing to do with how objects formed in that disc. I’m afraid I’m not following you. The definition of planet has nothing to do with how an object was formed. ---
**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:** [February 3, 2021, 12:49am UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/125 "2021-02-03T00:49:22Z")
> [@Northern\_Piper](#): > > I’m afraid I’m not following you. The definition of planet has nothing to do with how an object was formed. What you aren’t following is the science. The fact that millions of years after the end of planetary formation a rock in space is smashed to debris also has nothing to do with how an object was formed–and noting to do with “clearing its orbit” _which is about formation, not future distruction._ And _clearing its orbit_ is _absolutely_ about how it was formed. ---
**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 18, 2021, 3:30pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/126 "2021-02-18T15:30:54Z")
New study challenges Planet 9 hypothesis. Argues that it’s a sampling error in the Trans-Neptunian orbits. > **[Planet Nine Hypothesis Takes a Major Hit in New Study](https://www.extremetech.com/extreme/320048-planet-nine-hypothesis-takes-a-major-hit-in-new-study)** > > It used to be easy to know how many planets there were: nine. It had been nine planets for an entire generation before scientists started rethinking what counts as a planet. Pluto is out, but some astronomers believe there's a real ninth planet... ---
**Author:** ![PastTense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pasttense/32/14550_2.png) [@PastTense](https://boards.straightdope.com/u/PastTense)\ **Post date:** [December 18, 2024, 11:29pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/127 "2024-12-18T23:29:22Z")
New Scientific American article which notes: > Nobody has found [Planet Nine](https://www.scientificamerican.com/article/hidden-planet-x-could-orbit-in-outer-solar-system/) yet. If it’s really out there, it’s too far and too faint for almost any existing telescope to spot it. But that’s about to change. A new telescope, the [Vera C. Rubin Observatory](https://www.scientificamerican.com/article/how-to-move-the-worlds-largest-camera-from-a-california-lab-to-an-andes/) in Chile, is about to open its mechanical eyes. When it does, it should catch millions of previously undetected celestial phenomena, from distant supernovae to near-Earth asteroids—and, crucially, tens of thousands of new objects around and beyond Pluto. > > If Brown’s hidden world is real, Rubin will almost certainly find it or strong indirect evidence that it exists. “In the first year or two, we’re going to answer that question,” says Megan Schwamb, a planetary astronomer at Queen’s University Belfast in Northern Ireland—and, just maybe, the solar system will once again have a ninth planet. > **[We May Be on the Brink of Finding the Real Planet Nine](https://www.scientificamerican.com/article/if-planet-nine-exists-well-find-it-soon/)** > > If there’s a hidden world in the solar system, a new telescope should find it There was a discovery in April of significance: > **[Evidence for Planet 9 found in icy bodies sneaking past Neptune](https://www.space.com/planet-9-cometary-bodies-neptune-solar-system)** > > Something is throwing icy bodies past Neptune, and scientists have an interesting idea about what it might be. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [December 19, 2024, 1:20am UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/128 "2024-12-19T01:20:36Z")
Well there are a good number of dwarf planets out there, but finding one as big as say- Mars? Or a giant, that is gonna be tough. And sure, we could call Pluto a planet, but if so, there are at least 10 (Eris), maybe 12 “planets”. Pluto is way smaller ( it is .002 of what was originally estimated- not counting Lowells idea that is was 7x the mass of the Earth) ) than we originally thought, Charon was making it look larger. It is smaller than at least 7 moons. It is a fifth the size of the Moon. Yes, if Lowell was right and Pluto was 7x the mass of the earth, it would still be classed as a planet. Or even the later calculated estimate of 1 Earth mass. But this does sound interesting. let us see if it pans out to another actual planet or just more dwarf planets. ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [December 19, 2024, 1:28am UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/129 "2024-12-19T01:28:36Z")
> [@DrDeth](#): > > Well there are a good number of dwarf planets out there, but finding one as big as say- Mars? Or a giant, that is gonna be tough. I’ve seen more than one astronomer pretty confidently say that if there’s a ninth planet, Rubin will see it, such is its field of view and sensitivity. It’s pretty rare to hear this level of confidence so it’s pretty exciting. Of course, I also like the idea of the 9th planet actually being a tiny black hole, but in that case I don’t think Rubin is equipped to detect it. ETA: nope, I’m wrong, VRO will in fact be able to detect flares from a primordial black hole ([cite](https://www.astronomy.com/science/is-planet-nine-a-black-hole-or-a-planet-harvard-scientists-suggest-a-way-to-find-out/))! ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [December 19, 2024, 1:30am UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/130 "2024-12-19T01:30:48Z")
> [@Mijin](#): > > I’ve seen more than one astronomer pretty confidently say that if there’s a ninth planet, Rubin will see it, such is its field of view and sensitivity. It’s pretty rare to hear this level of confidence so it’s pretty exciting. I hope it occurs. I expect he will detect something, anyway. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [December 19, 2024, 2:58am UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/131 "2024-12-19T02:58:23Z")
> [@Mijin](#): > > I’ve seen more than one astronomer pretty confidently say that if there’s a ninth planet, Rubin will see it, such is its field of view and sensitivity. Sure Rubin will see it, but who’s going to pick it out of all the noise and clutter etc. that that telescope will produce? Some of the telescopes we have today could see it and probably have. But no one’s identified it yet. ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [December 19, 2024, 3:08am UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/132 "2024-12-19T03:08:17Z")
But I think they mean see it and recognize it for what it is. It will repeatedly make surveys of the whole sky and be able to spot virtually anything moving. Pretty much the same thing we’ve been doing on patches of the sky, and making important discoveries as we go, but now, basically, no stone left unturned. ---
**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:** [December 19, 2024, 3:15am UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/133 "2024-12-19T03:15:29Z")
Pretty much any decent telescope would be able to see it, once you know exactly where to look, and spend enough time exposing. When they say they’ll be able to find it, they mean picking it out of the noise. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [December 19, 2024, 3:27am UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/134 "2024-12-19T03:27:27Z")
How much of the sky (i.e. our solar system) has been surveyed from earth? 10%, 50%, 75%, 100%? (really asking) ---
**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:** [December 19, 2024, 3:31am UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/135 "2024-12-19T03:31:23Z")
Depends on what standards you set for the survey. A human near the Equator can scan the entire sky over the course of a year, but only at the naked-eye level. The Sloan Digital Sky Survey has done the entire sky several times over, at a much better than naked-eye level, but there’s still a lot it can miss. At the other end of the scale, only a few square degrees have gotten the Ultra-Deep-Field treatment. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [December 19, 2024, 3:42am UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/136 "2024-12-19T03:42:40Z")
I have photos of the mirror for this telescope being made. Proudly made at the U of A in Tucson, AZ ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [December 19, 2024, 7:08am UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/137 "2024-12-19T07:08:20Z")
> [@PastTense](#): > > There was a discovery in April of significance: > > [Evidence for Planet 9 found in icy bodies sneaking past Neptune | Space](https://www.space.com/planet-9-cometary-bodies-neptune-solar-system) I haven’t read Brown’s and Batygin’s paper, but I note they dismiss the possibility that various passing stars could be the culprits in sending TNOs into Neptune-crossing orbits: > [@](#): > > The studied TNOs, and any on similar paths, don’t spend too much time in their orbits; over the course of millions of years the gravity of the azure blue ice giant Neptune inevitably bats them away, scattering them far and wide and sometimes even out of the solar system entirely. This means that whatever is sending TNOs onto Neptune-crossing orbits is doing so continuously. There must be an ongoing process in place to keep the TNO supply replenished. This means that the culprit can’t be something that happened in the distant past, like a star passing particularly close by. It has to be something that still exists. The problem with this is that passing stars are not something from the “distant past”. Rather they happen fairly frequently, in astronomical terms. On average, a star will pass through the Oort Cloud (roughly 1 light year away) about once every 100,000 years. The most recent was Scholz’s Star, that passed by only 80,000 years ago. As far as the Rubin Telescope, it’s going to image the same field of stars several times, either on the same night or on successive nights and then those images will be automatically compared and differences found will be reported. So people don’t have to blink-compare images like what was done to discover Pluto. However, they expect something like 10 million differences to be reported every night! Yeah, the vast majority of those differences will just be noise, but then people† have to sort through them to find the relative few that are meaningful. So yes, they might find Planet 9 in the first year. Or it may take much longer. †The general public will be able to help with this. You can sign up with Zooniverse if you want to join in. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [December 25, 2024, 10:14pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/138 "2024-12-25T22:14:59Z")
> [@Whack-a-Mole](#): > > How much of the sky (i.e. our solar system) has been surveyed from earth? 10%, 50%, 75%, 100%? (really asking) By a telescope form a few decades ago? 100%. They commonly took pictures of the entire night sky, and examined them for fuzzy or moving objects. Mind you they had no way back then of seeing stuff like Eris. Or this hypothetical 9th planet. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [December 25, 2024, 10:57pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/139 "2024-12-25T22:57:21Z")
> [@DrDeth](#): > > Mind you they had no way back then of seeing stuff like Eris. Or this hypothetical 9th planet. Eris, at apparent magnitude 18.7, is quite bright for a Kuiper Belt Object. That would have been very easily found by telescopes going back more than a century. The first KBO (after Pluto) discovered was 1992 QB1 (now known as 15760 Albion) has an apparent magnitude of 23.3, which could also have been found by telescopes for a long time. It was discovered in 1992, after all, and could have been discovered much earlier. However, they had to make an extremely long exposure to find it, which is something most astronomers rarely did. But note that they discovered it with a 2.2 meter telescope. By today’s standard, that’s a fairly small professional telescope. With larger telescopes, they don’t need quite as long exposures. ---
**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:** [December 25, 2024, 11:08pm UTC](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771/140 "2024-12-25T23:08:15Z")
Yeah, there’s alway a tradeoff. To do full-sky surveys, and especially to do them repeatedly (so you can see that objects are moving), you need some combination of large field of view and short exposures. To detect faint objects, you need some combination of small fields of view and long exposures. In both cases, more aperture always helps, but more aperture is generally very expensive, and at the high end introduces its own problems. And unfortunately, you need both wide, repeated surveys and detection of faint objects to discover things like new Kuiper belt objects. Once you’ve discovered them, it gets a lot easier, because now you don’t have to look at the full sky, just where the object is, and so you can switch to just doing small-field long-exposure work, without the tradeoff. But first you have to know where to look. [Previous page](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771.md?page=6) [Next page](https://boards.straightdope.com/t/is-there-really-a-planet-9-out-there-in-the-kuiper-belt/931771.md?page=8)