# How long will it be before the planets are in the same position as they are now? **URL:** \ **Category:** Factual Questions\ **Created:** [October 16, 2022, 3:23am UTC](https://boards.straightdope.com/t/how-long-will-it-be-before-the-planets-are-in-the-same-position-as-they-are-now/973317 "2022-10-16T03:23:22Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Nars\_Glinley](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nars_glinley/32/8177_2.png) [@Nars\_Glinley](https://boards.straightdope.com/u/Nars_Glinley)\ **Post date:** [October 16, 2022, 4:53pm UTC](https://boards.straightdope.com/t/how-long-will-it-be-before-the-planets-are-in-the-same-position-as-they-are-now/973317/21 "2022-10-16T16:53:36Z")
No, I don’t. I guess because I’m old and was taught that there were 9 planets. ---
**Author:** ![glowacks](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/glowacks/32/5548_2.png) [@glowacks](https://boards.straightdope.com/u/glowacks)\ **Post date:** [October 16, 2022, 4:54pm UTC](https://boards.straightdope.com/t/how-long-will-it-be-before-the-planets-are-in-the-same-position-as-they-are-now/973317/22 "2022-10-16T16:54:32Z")
> [@Darren\_Garrison](#): > > Just curious, are you including Eris, Haumea, Makemake, Gonggong, Quaoar, Sedna, Orcus and Salacia in your list for planetary alignment? If not, why not? I was just about the ask the same thing, at least with respect to Eris, which has a better claim at being a planet than Pluto; Pluto’s only claim to fame in that it was discovered first, which was entirely an accident. ---
**Author:** ![glowacks](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/glowacks/32/5548_2.png) [@glowacks](https://boards.straightdope.com/u/glowacks)\ **Post date:** [October 16, 2022, 4:57pm UTC](https://boards.straightdope.com/t/how-long-will-it-be-before-the-planets-are-in-the-same-position-as-they-are-now/973317/23 "2022-10-16T16:57:36Z")
> [@Nars\_Glinley](#): > > No, I don’t. I guess because I’m old and was taught that there were 9 planets. There still very well may be 9 planets, though the 9th won’t be Pluto. There is some circumstantial evidence of another planetary body much further out than the current 8 official planets, based on some patterns in the orbits of the other dwarf planets that have been discovered out there. Nothing to suggest that we have any idea where it is, but the alignment of the orbits of the dwarf planets suggests that something’s missing. > **[Planet Nine](https://en.wikipedia.org/wiki/Planet_Nine)** > > Planet Nine is a hypothetical ninth planet in the outer region of the Solar System. Its gravitational effects could explain the peculiar clustering of orbits for a group of extreme trans-Neptunian objects (ETNOs), bodies beyond Neptune that orbit the Sun at distances averaging more than 250 times that of the Earth. These ETNOs tend to make their closest approaches to the Sun in one sector, and their orbits are similarly tilted. These alignments suggest that an undiscovered planet may be she Ba... ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [October 16, 2022, 5:00pm UTC](https://boards.straightdope.com/t/how-long-will-it-be-before-the-planets-are-in-the-same-position-as-they-are-now/973317/24 "2022-10-16T17:00:05Z")
Maybe that’s a better metric. How long till the planets are all in the same quadrant, and how long till they will be in the same quadrant again? As stated upthread, the more precise we are looking, the longer it will take (up to infinity), so maybe it makes more sense to drop the precision until we get a number that is reasonable. ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [October 16, 2022, 5:02pm UTC](https://boards.straightdope.com/t/how-long-will-it-be-before-the-planets-are-in-the-same-position-as-they-are-now/973317/25 "2022-10-16T17:02:23Z")
> [@glowacks](#): > > I was just about the ask the same thing, at least with respect to Eris, which has a better claim at being a planet than Pluto; Pluto’s only claim to fame in that it was discovered first, which was entirely an accident. Right, if we found another planet that was say Neptune size way out there, we’d likely call it a planet, as it shares many properties we associate with planets. If Pluto is a planet, then anything that shares properties with it is a planet, and now we got dozens of them. ---
**Author:** ![Czarcasm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/czarcasm/32/4050_2.png) [@Czarcasm](https://boards.straightdope.com/u/Czarcasm)\ **Post date:** [October 16, 2022, 5:11pm UTC](https://boards.straightdope.com/t/how-long-will-it-be-before-the-planets-are-in-the-same-position-as-they-are-now/973317/26 "2022-10-16T17:11:55Z")
The twelfth of never…and that’s a long, long time. ---
**Author:** ![SuntanLotion](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/suntanlotion/32/16165_2.png) [@SuntanLotion](https://boards.straightdope.com/u/SuntanLotion)\ **Post date:** [October 16, 2022, 5:38pm UTC](https://boards.straightdope.com/t/how-long-will-it-be-before-the-planets-are-in-the-same-position-as-they-are-now/973317/27 "2022-10-16T17:38:27Z")
Theres a nice book about it called How I killed Pluto and why it had it coming by a Mr. Brown. ---
**Author:** ![Babale](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/babale/32/15666_2.png) [@Babale](https://boards.straightdope.com/u/Babale)\ **Post date:** [October 16, 2022, 5:42pm UTC](https://boards.straightdope.com/t/how-long-will-it-be-before-the-planets-are-in-the-same-position-as-they-are-now/973317/28 "2022-10-16T17:42:11Z")
> [@k9bfriender](#): > > Right, if we found another planet that was say Neptune size way out there, we’d likely call it a planet, as it shares many properties we associate with planets. If there IS another gas or ice giant way out there, would the size of its orbit mean that it is less likely to have cleared it of smaller bodies, thus preventing it from being a planet under the current definition? ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [October 16, 2022, 6:17pm UTC](https://boards.straightdope.com/t/how-long-will-it-be-before-the-planets-are-in-the-same-position-as-they-are-now/973317/29 "2022-10-16T18:17:33Z")
It’s not clearing it of smaller objects that defines it, it is clearing it of objects of comparable size. > **[Clearing the neighbourhood](https://en.wikipedia.org/wiki/Clearing_the_neighbourhood)** > > "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 in 2006 by the International Astronomical Union (I... ---
**Author:** ![dolphinboy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dolphinboy/32/330_2.png) [@dolphinboy](https://boards.straightdope.com/u/dolphinboy)\ **Post date:** [October 16, 2022, 6:26pm UTC](https://boards.straightdope.com/t/how-long-will-it-be-before-the-planets-are-in-the-same-position-as-they-are-now/973317/30 "2022-10-16T18:26:54Z")
Thanks, SuntanLotion. I was never really a big fan of Pluto as a planet. As a kid, it didn’t seem to fit in with the others for some reason. I now think calling Pluto a Dwarf Planet is a fair compromise. I just didn’t know there were other dwarf planets in our solar system. Live and learn. ---
**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:** [October 16, 2022, 6:47pm UTC](https://boards.straightdope.com/t/how-long-will-it-be-before-the-planets-are-in-the-same-position-as-they-are-now/973317/31 "2022-10-16T18:47:12Z")
It actually doesn’t matter much whether we count Pluto or not, because it has an orbital resonance with Neptune. So if after some period we get Neptune in the same place, then Pluto will also be in the same place either in that same period, or a small multiple of the period. ---
**Author:** ![ekedolphin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ekedolphin/32/10003_2.png) [@ekedolphin](https://boards.straightdope.com/u/ekedolphin)\ **Post date:** [October 16, 2022, 6:56pm UTC](https://boards.straightdope.com/t/how-long-will-it-be-before-the-planets-are-in-the-same-position-as-they-are-now/973317/32 "2022-10-16T18:56:25Z")
I’m not saying that demoting a planet named after the god of the underworld and death caused his wrath to come down upon Earth, but… _[gestures at everything]_ ---
**Author:** ![mbh](https://avatars.discourse-cdn.com/v4/letter/m/a6a055/32.png) [@mbh](https://boards.straightdope.com/u/mbh)\ **Post date:** [October 16, 2022, 7:21pm UTC](https://boards.straightdope.com/t/how-long-will-it-be-before-the-planets-are-in-the-same-position-as-they-are-now/973317/33 "2022-10-16T19:21:19Z")
Does it want to be called a Dwarf Planet? Would it prefer to be called a Little Planet? Or an Achondroplastic Planet? ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [October 16, 2022, 7:35pm UTC](https://boards.straightdope.com/t/how-long-will-it-be-before-the-planets-are-in-the-same-position-as-they-are-now/973317/34 "2022-10-16T19:35:10Z")
> [@dolphinboy](#): > > Was this one of the reasons Pluto was demoted? I’m just curious what the reasoning was. The real reason is that we started to discover a lot of objects that were roughly the same size as Pluto out beyond Neptune, and it was theorized that objects like this were not all that uncommon. This created a problem for astronomers. Either Pluto gets demoted, or we start adding planets to the solar system, possibly by the dozens. Ceres, Pallas, Juno, Vesta, Astraea, Hebe, and Iris were all considered to be planets when they were discovered in the early to mid 1800s. But they had the same issue that Pluto had. Once we realized that the asteroid belt had lots of stuff in it, either we demoted all of these objects or we added lots and lots of planets to the known solar system. So, same as Pluto, Ceres and all of the other similar objects got demoted and by the late 1800s they were no longer considered to be planets. The problem for Pluto was as much political as it was scientific. Everyone grew up with nine planets, and a lot of folks wanted to keep Pluto as a planet. But then the trick is how do you define Pluto as a planet and all of these new objects as non-planets? You can’t go by size. At the time, Eris was thought to be larger than Pluto (the latest measurements now have it as slightly smaller than Pluto) and it is quite possible that there are dozens and dozens of objects out there that are larger than Pluto, as well as many that are smaller. And they are all basically little ice balls like Pluto. There really was no good scientific definition that could be used that would included Pluto as a planet but exclude objects like Eris. So how do you satisfy the folks that want a rigorous scientific definition of a plant and also satisfy those who want to keep Pluto as a planet? They came up with the idea of calling Pluto and similar objects “dwarf planets”. This compromise allowed Pluto to still be planet-ish (and not get completely demoted into an asteroid type object), while still using a scientific definition of what a planet is that applied to all objects in the solar system. The next argument, which hasn’t been settled yet by the way, is what exactly the definition of a dwarf planet is. We have a formal definition for a planet, but not a formal definition of a dwarf planet. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [October 16, 2022, 8:34pm UTC](https://boards.straightdope.com/t/how-long-will-it-be-before-the-planets-are-in-the-same-position-as-they-are-now/973317/35 "2022-10-16T20:34:42Z")
> [@engineer\_comp\_geek](#): > > The next argument, which hasn’t been settled yet by the way, is what exactly the definition of a dwarf planet is. We have a formal definition for a planet, but not a formal definition of a dwarf planet. Unlikely the IAU will come up with one. The main reason we have a definition for planets is bureaucratic. The IAU has the remit to name astronomical objects and the features on them. (How they got this remit, I don’t know.) To do this, they have two naming committees, one for planets and one for smaller bodies. When Tran-Neptunian Objects (TNOs) started to be discovered in significant numbers in the 90s, they realized that there would eventually be discovered some object or objects that would push the boundaries between what was considered a planet and what was not. So they tried to come up with a definition of planet so that when one was discovered, they’d be able to assign naming it to the right committee. They failed. Twice. The current definition was the third attempt and what we got was a kludge. The problem was that the issue was really bureaucratic, but they were trying to do it scientifically. And there is no good scientific definition of a planet. Anyway, there is no bureaucratic reason for them to come up with a definition of dwarf planet, so they won’t try to make one. The current dwarf planets are lumped with the small bodies as far as the naming committees go, so there’s no pressure on the IAU to try to define them. Or even assign more bodies to that category, which they have not done since the original five were named. ---
**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:** [October 16, 2022, 8:51pm UTC](https://boards.straightdope.com/t/how-long-will-it-be-before-the-planets-are-in-the-same-position-as-they-are-now/973317/36 "2022-10-16T20:51:23Z")
> [@engineer\_comp\_geek](#): > > Eris was thought to be larger than Pluto (the latest measurements now have it as slightly smaller than Pluto) Smaller diameter than Pluto but significantly more massive. ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [October 16, 2022, 8:54pm UTC](https://boards.straightdope.com/t/how-long-will-it-be-before-the-planets-are-in-the-same-position-as-they-are-now/973317/37 "2022-10-16T20:54:09Z")
> [@engineer\_comp\_geek](#): > > This compromise allowed Pluto to still be planet-ish (and not get completely demoted into an asteroid type object), while still using a scientific definition of what a planet is that applied to all objects in the solar system. And they gave Pluto the honor of calling these planets Plutoids. ---
**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:** [October 16, 2022, 9:12pm UTC](https://boards.straightdope.com/t/how-long-will-it-be-before-the-planets-are-in-the-same-position-as-they-are-now/973317/38 "2022-10-16T21:12:43Z")
Yeah, personally, I’m proud for Pluto. Back when it was considered a planet, it was the red-headed stepchild of the planets: The smallest by far, in by far the most eccentric and inclined orbit, perturbed by its moon(s) to an unprecedented degree, etc. Now, though, it’s, if not quite the largest of the Kuiper belt objects, certainly still a prince among them. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [October 17, 2022, 1:40am UTC](https://boards.straightdope.com/t/how-long-will-it-be-before-the-planets-are-in-the-same-position-as-they-are-now/973317/39 "2022-10-17T01:40:09Z")
> [@Chronos](#): > > Back when it was considered a planet, it was the red-headed stepchild of the planets: That’s the wrong metaphore. More that it was the ugly duckling of the planets. Because just as the ugly duckling wasn’t really a duck, Pluto wasn’t really a planet. > [@Chronos](#): > > Now, though, it’s, if not quite the largest of the Kuiper belt objects, In terms of physical size, it’s the largest currently known, but only the second most massive. For astronomers, mass is actually the most important quantity for an astronomical body. Size is important, but not quite as important as mass. ---
**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:** [October 17, 2022, 3:03pm UTC](https://boards.straightdope.com/t/how-long-will-it-be-before-the-planets-are-in-the-same-position-as-they-are-now/973317/40 "2022-10-17T15:03:19Z")
> [@ekedolphin](#): > > I’m not saying that demoting a planet named after the god of the underworld and death caused his wrath to come down upon Earth, but… > > _[gestures at everything]_ Nice planet ya’ got here. Be a shame if anything _happened_ to it. [Previous page](https://boards.straightdope.com/t/how-long-will-it-be-before-the-planets-are-in-the-same-position-as-they-are-now/973317.md?page=1) [Next page](https://boards.straightdope.com/t/how-long-will-it-be-before-the-planets-are-in-the-same-position-as-they-are-now/973317.md?page=3)