Talk:Orcus (dwarf planet)

Mass listing

Added missing "." in Mass listing on table. Abyssoft 21:08, 5 July 2006 (UTC)

Diameter

From “IAU's Planet Definition” Questions & Answers Sheet:[1]

(90482) Orcus   1000±200 km [Brown, Binzel, private communication (2006)]

It may be much smaller than thought.--JyriL ^talk 14:04, 16 August 2006 (UTC)

So what's up with the listed dimensions for Orcus?: "946.3+74.1-72.3 km.", it looks like it could be formatted better. I'll leave the correction for someone who knows better. HunterTruth (talk) 16:17, 26 January 2008 (UTC)

In the intro: "The diameter of Orcus is estimated to be 761 or 807 km and the diameter of Vanth 378 or 267 km respectively, depending on their relative albedos."
In the info-box: "Dimensions 917±25 km"
In the section, "Size and magnitude": "If the albedos of both bodies are the same at 0.23 then the size of Orcus is about 917±25 km, and the size of Vanth is about 276±17 km."
There's a big inconsistency between the intro and the Size&Mag section, and given the various estimates of albedo, the ±25 km in the info-box doesn't actually show the full error-range.

Additionally, the info-box should specify what the 917km actually refers to; diameter, radius, major axis, etc, not just "Dimensions". -- PaulxSA (talk) 06:16, 23 February 2017 (UTC)

Sources / possible satellite

I do not believe that we should use proposals as references. After all, if an astronomer wants to get a grant/telescope time etc. he could mention the possibility that the object is … inhabited. I feel we should keep with the usual sources. Let Mr Brown publish first. Eurocommuter 16:08, 21 August 2006 (UTC)

Agreed. It's a good example of intriguing information that could mentioned on the talk page. Suggestive/speculative information doesn't belong to article itself.--JyriL ^talk 19:03, 21 August 2006 (UTC)

I can't help but think it is a bit outrageous to suggest that Mr. Brown lied about something so important to his work just to get telescope time. JamesFox 01:29, 23 August 2006 (UTC)

This was certainly not my point! My point was that with Google one can find many documents and not all of them should be used as references. Astronomers have data /hypothesis they want to test. They decide what and when to publish. I simply belive that we should let them to do so and then report it. My apologies, if my comment was read otherwise.Eurocommuter 10:10, 23 August 2006 (UTC)

Except that from the proposal, I get the impression that the satellite of Orcus is regarded as fact by Michael Brown (just not announced), due to the phrasing used, and that the telescope time was to get data necessary to compute the orbital period, not to confirm the existance of the satellite. JamesFox 19:24, 24 August 2006 (UTC)

Yeah, but he hasn't published any evidence to prove a satellite. If there is one, he'll publish when he's ready. I'm sure he himself would rather confirm it first, rather than have his funding proposals used as evidence. The Singing Badger 20:26, 24 August 2006 (UTC)

The discovery of a satellite for Orcus has been published in IAUC 8812, but I haven't actually seen the circular, so I have no details. RandomCritic 02:03, 25 February 2007 (UTC)

I tried to track down info as well, but met with the same problem. Is the existence of this page, with the heading "Recently Discovered Natural Satellites and Rings of Major and Minor Planets" and the text "Satellites of 2003 AZ_84, (50000) Quaoar, (55637) 2002 UX_25, and (90482) Orcus. IAUC 8812, 2007 Feb. 22" enough to warrant a mention? Something like "An IAU circular dated 22 February 2007 announced the discovery of satellites for Quaoar and Orcus"? Thoughts? --Ckatz^chat_spy 11:54, 25 February 2007 (UTC)

Albedo

this change in the Albedo does not make sense. It is way too high' and I could not find any sources for it. I am changing back to the 0.09 value. Chagai 18:47, 26 October 2007 (UTC)

It says right in the text that observations from the Spitzer Space Telescope were used to derive a size, which can the be used to get a value for the albedo, which is given in the text as ~20%. I'm going to revert. JamesFox 02:35, 27 October 2007 (UTC)

We need a source, and a good one. this source is reliable, and support 0.09. If you are familiar with the term Albedo, you know that 20% is impossible! Its like a mirror, which "90482 Orcus" is not. Look at the values of other Trans-Neptun objects. They don't even come close. Chagai 01:51, 28 October 2007 (UTC)

See also Bond albedo. All values are fractions. You are just putting here wrong information. Chagai 11:26, 29 October 2007 (UTC)

There are many, many errors in your statements. I'll list at least most of them. 1) 20% is not an impossible amount, it is not close to being a mirror. 2) 20% is a fraction, it is the same as 0.2, just as 0.09 is the same as 9%. 3) Several known TNO's have albedos higher than 0.2, or 20%. Pluto has an estimated albedo of 0.49 to 0.66 (or between 49% and 66%), Eris' albedo is given as being around 86% (0.86). 4) There is a reference for the values determied by the Spitzer Space Telescope, look at reference 1. 5) The 0.09 value should nor be considered better, since if you look at the sources, it is clear that that Albedo was simply assumed, back in the days when Astronomers thought that TNO's would have low albedos. JamesFox 14:38, 3 November 2007 (UTC)

Vanth

Mike Brown just named Orcus's moon. But it's not official until he clears it with the IAU. So should we start making the changes now, to make things easier, or should we wait until it's confirmed beyond doubt? Serendi^podous 20:00, 7 April 2009 (UTC)

Technically the name has merely been submitted and could be turned down. But we should definitely mention that the name has been submitted to the IAU for review. -- Kheider (talk) 20:14, 7 April 2009 (UTC)

Done :) Iridia (talk) 03:05, 8 April 2009 (UTC)

Oh, if anyone wants to have a look at it, I went looking and found the discovery image of Orcus + moon here in the HST archive (Aladin Java applet will load). Iridia (talk) 03:13, 8 April 2009 (UTC)

I went ahead and created Vanth (moon). Didn't want to link it into this article until it was official, but that is just a technicality. kwami (talk) 00:03, 15 April 2009 (UTC)

No! This is a bad idea. It is definitely not 'just' a technicality. Vanth is not the name yet, it remains Orcus I. Did you not see the whole debacle over the premature publicising of the naming of Sedna? (Though, nice job on the little moon-article...) Iridia (talk) 04:38, 15 April 2009 (UTC)

Okay, I'll move it to 90482 Orcus I and we can move again if/when the name is approved. kwami (talk) 06:54, 15 April 2009 (UTC)

Thanks. And cheers for getting back to it so quickly ;) Iridia (talk) 07:01, 16 April 2009 (UTC)

Faster rotation period?

The following paper:

Ortiz, J. L. (2011). "A mid-term astrometric and photometric study of trans-Neptunian object (90482) Orcus". Astronomy and Astrophysics. 525. Bibcode:2011A&A...525A..31O. doi:10.1051/0004-6361/201015309. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)

suggests that the ~10h periodic variability may be caused by the orbit of the satellite and hence the rotation of Orcus might be much faster. For what it's worth.—RJH (talk) 22:58, 7 December 2010 (UTC)

Actually it claims that there is a 9.7 day photometric periodicity coincident with the orbital motion in addition to weaker 10h periodicity of unknown origin. Ruslik_Zero 06:59, 8 December 2010 (UTC)

Dead link

During several automated bot runs the following external link was found to be unavailable. Please check if the link is in fact down and fix or remove it in that case!

• http://www.cfa.harvard.edu/iauc/08800/08812.html
  • In (55637) 2002 UX25 on 2011-05-20 21:18:17, 404 Not Found
  • In (55637) 2002 UX25 on 2011-05-31 04:15:46, 404 Not Found
  • In 90482 Orcus on 2011-06-19 21:44:28, 404 Not Found

--JeffGBot (talk) 21:45, 19 June 2011 (UTC)

Move without consensus?

To move the article without prior consensus is a complete mystery to me. The given rationale is not good enough and will cause an administrative nightmare. Guess this opens the door to endless discussions about which TNO is or is not a DP. It's crazy... -- Cheers, Rfassbind – talk 22:56, 18 September 2015 (UTC)

This article should not have been moved and needs to be moved back by an admin. -- Kheider (talk) 22:58, 18 September 2015 (UTC)

I prefer the original article name. The claim in the move comment that "Literally every source calls it a dwarf planet" isn't accurate, at least two sources in this article decline to call it a dwarf planet, namely ref #22 IAU and ref #23 NASA. —RP88 ^(talk) 23:04, 18 September 2015 (UTC)

Moved the page myself, as I gave up my hope he would come to his senses and change his mind. I also fixed half a dozen redirects. I think the term for wasting everybody's time is disruptive editing. When will this end? -- Rfassbind – talk 00:51, 19 September 2015 (UTC)

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New Category > Category:90482 Orcus

On 1 April 2015, the category Category:90482 Orcus has been created and added to the article's categories. Although I don't think this category makes much sense, there might be a rationale I'm missing. Can its creator, Solomonfromfinland, or anyone else help me understand? Rfassbind – talk 23:31, 2 April 2017 (UTC)

Right now, there are only three articles in said category: this article, Orcus, and Vanth (the latter two refer to the deities, not the dwarf planet and its moon). However, having said latter two articles in said category is arguably justified; the article Orcus has an entire paragraf on the plutino (wikilinks removed):

The Kuiper belt object 90482 Orcus is named after Orcus. This was because Orcus was sometimes considered to be another name for Pluto, and also because Pluto and 90482 Orcus are both plutinos.

Meanwhile, the article Vanth has a hatnote:

For the moon, see Vanth (moon).

(Wikilink as in original; “Vanth (moon)” redirects to “90482 Orcus”.) However, the number of articles in this category could be increased to four by restoring “Vanth (moon)” as a separate article, as I think should be done; after all, we have articles on Solar System objects of which about as little is known as is about Vanth.--Solomonfromfinland (talk) 17:25, 8 April 2017 (UTC)

I disagree, WP:OSE is a weak argument. —MartinZ (talk) 15:13, 9 April 2017 (UTC)

Btw, the correct date is April 2017, not April 2015. (I'm not offended by said mistake; I just wanted to point it out politely.)--Solomonfromfinland (talk) 17:28, 8 April 2017 (UTC)

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GA Review

This review is transcluded from Talk:90482 Orcus/GA1. The edit link for this section can be used to add comments to the review.

Reviewer: Bryanrutherford0 (talk · contribs) 14:18, 20 September 2019 (UTC)

GA review (see here for what the criteria are, and here for what they are not)

1. It is reasonably well written.

   a (prose, spelling, and grammar): b (MoS for lead, layout, word choice, fiction, and lists):

   The article is written to a good prose standard and complies with the required sections of MoS, with one exception: the lead section is clear and relevant but a bit too long. MOS:LEADLENGTH indicates that the lead section of an article this size should be "one or two paragraphs." The final paragraph should be cut from the lead, since it appears to only contain information about Vanth and not Orcus; that content should be moved to the section on Vanth at the end of the body, where it will give that section a little more heft (I would put it between the two existing sentences of the final paragraph of the body).

   I think the third paragraph of the lead should probably be cut as well (of course keeping all of the content in the body sections on Orcus's surface and cryovolcanism). I would probably keep the first sentence ("The surface of Orcus is...") but move it to the first paragraph after the sentence that establishes the body's diameter, which would improve the size balance between the two paragraphs. The rest of the detail here probably needs to wait for treatment in the body.

   In the section "Size and magnitude", one sentence begins, "If the albedos of both bodies are the same...", but the next sentence says that a subsequent study has revealed that the albedos are not the same, requiring an upward revision of Vanth's estimated size; if that's true, then the "If they were the same..." sentence should be deleted as a distraction.

   In "Spectra and surface", The first sentence of the third paragraph begins, "Orcus straddles the edge...", but to straddle something is to be on both sides of it at once. It's not yet known with certainty whether Orcus is big enough, but in reality it either is or is not, so "straddles" sends the wrong message. Maybe "Orcus sits at the threshold..."?

   Regarding the use of Template:Minor planets navigator at the end: it doesn't seem like this footer navbox is really adding anything to the article without the adjacent minor planets included, but I see that we don't seem to have articles about either of them (and may never have, since neither may ever be especially notable). Probably this should be removed, unless it's serving some purpose I'm not seeing?

   Another minor note: I would add a wikilink to psychopomp in the sentence in "Name" explaining Vanth's name, but it's not required.

2. It is factually accurate and verifiable.

   a (reference section): b (citations to reliable sources): c (OR): d (copyvio and plagiarism):

   The article has citations and a reference section. The online citations included support the vast majority of the article's substantive content, and I'll AGF on some of the paywalled studies for plausible physical data. Earwig's copyvio tool shows a close match between some of this article's text about the IAU's naming conventions and some other wiki/fansites, but it looks to me like that's probably because those sites ripped off this article.

   Comments: I see in the infobox that we have the margins of error for all the figures in the "Physical characteristics" section, but they seem to be omitted in the "Orbital characteristics" section. Is there a reason not to include the uncertainties with those figures as well? They seem to be included on the JPL page that's cited, in the form of standard deviations (rather than a 90% confidence interval or what have you). Also, the JPL page's orbital data seem to be based on Epoch 2019 April 27.0 (as do those on the Minor Planet Center page), but the infobox claims that its orbital characteristics figures are from Epoch 4 September 2017; where did the infobox numbers come from, and should they be replaced by the figures from the JPL site?

   The section "Mass and density" speculates about the division of mass between Orcus and Vanth, but the preceding section ("Size and magnitude") seems to indicate that a 2017 study nailed down Vanth's diameter to within about ±2%. Does this datum render the talk about Vanth making up between 1/33 and 1/12 of the binary system's mass outdated? If the previous section is correct, then it sounds like the relative sizes are known to much greater precision than this now.

   In "Orbit and rotation", I'm uncomfortable with the phrase "Orcus is currently 48.0 AU from the Sun"; this is a sort of claim that is certain to rapidly go out of date and need continual updating. Perhaps we could cut this out and then update the remainder of the sentence to something like "Orcus has its aphelion in 2019 and will then approach the Sun until reaching perihelion in [presumably about] 2143"? That at least would keep the article up to date for the next 124 years. The second paragraph in the same section includes the claim that a rotational period of "about 10.5 hours seems to be the most likely one." Why does that figure seem the most likely, if other studies have produced other figures? Indeed, the abstract of the cited article seems to me to suggest that its authors find the possibility of Vanth's being tidally locked to be at least plausible. This claim about likelihood doesn't seem warranted by the sources I can see (but the Ortiz et al. article is paywalled, so I can't read the full text).

   I've updated the orbital parameters of Orcus from the JPL Small Body Database. About the uncertainties for the orbital characteristics, the figures in the infobox are rounded and the uncertainties listed on the JPL site are very small. There is no need to include the small uncertainties if nearly all of them don't exceed 0.001. Nrco0e (talk) 01:59, 23 September 2019 (UTC)

   With that aside, I have resolved the rest of your assessments. Nrco0e (talk) 02:28, 23 September 2019 (UTC)

   Oh, I see, the uncertainty is beyond the precision you're reporting. Fair enough! -Bryan Rutherford (talk) 14:43, 23 September 2019 (UTC)

3. It is broad in its coverage.

   a (major aspects): b (focused):

   The article appears to cover the major aspects of the topic, including observational history, origin of name, characteristics of the body and of its orbit, and a brief summary of information about its moon. It also doesn't generally drift off topic, with a few exceptions: the chief is that it goes into too much detail about Vanth in the lead section (as discussed above). Another two come in the "Name" section, where the sentence describing the visual depiction of the deity Orcus in Etruscan tombs should be completely removed. In the same section, the discoverer's wife's given name isn't relevant and should be removed in the interest of privacy.

4. It follows the neutral point of view policy.

   Fair representation without bias:

   The article maintains an appropriately neutral tone and doesn't e.g. lionize the body's discoverers.

5. It is stable.

   No edit wars, etc.:

6. It is illustrated by images and other media, where possible and appropriate.

   a (images are tagged and non-free content have fair use rationales): b (appropriate use with suitable captions):

   The images are relevant and appropriate, and they all have good licenses and helpful captions. It would be nice to add alt-text to all the images, but it isn't required for GA.

7. Overall:

   Pass/Fail:

   An interesting and informative article about a plutino! With a little polish, this should be able to reach the GA standard.

I have edited the article according to your recommendations. I will be waiting for your next assessments. Nrco0e (talk) 19:07, 21 September 2019 (UTC)

Wow, thank you for your quick and responsive editing! I'll look through the sources by the end of the day tomorrow and give any feedback there, but everything I've pointed out so far is now fixed. -Bryan Rutherford (talk) 20:38, 21 September 2019 (UTC)

By the way, if you haven't known already, most of the scientific papers cited in the article can be accessed from their arXiv preprints, which is linked near the end of the source citation. For your issue about the rotation period of Orcus, the full paper can be read at https://arxiv.org/abs/1010.6187. I hope this helps for your future reviews on science-related articles! Nrco0e (talk) 02:40, 23 September 2019 (UTC)

This all looks good! Thanks again for being so responsive; this article is hereby approved for GA! -Bryan Rutherford (talk) 14:43, 23 September 2019 (UTC)

Leaked image of Orcus?

https://www.youtube.com/watch?v=2rrelv96nCQ

I am not a believer in the Nibiru cataclysm, so what is in that final image? 103.38.21.38 (talk) 05:25, 15 December 2019 (UTC)

As it is meaningless youtube clickbait, it could be anything such as a manipulated image of the bottom of a frying pan. -- Kheider (talk) 11:59, 15 December 2019 (UTC)

Exploration

Will there be a mission to orcus? — Preceding unsigned comment added by Zachbarbo (talk • contribs) 19:46, 9 November 2021 (UTC)

I wish! A concept has been studied, though it also considers Pluto, Haumea, and Quaoar as possibilities. But only a concept. Double sharp (talk) 23:06, 9 November 2021 (UTC)

Flyby

How long will a flyby mission to Orcus will take? — Preceding unsigned comment added by Zachbarbo (talk • contribs) 15:12, 10 November 2021 (UTC)

Orcus is currently at 48 AU, Pluto at about 30. It took New Horizons almost 15 years to reach Pluto. So, all things being equal, we could expect it to take maybe 24 years to reach Orcus. But all things wouldn't be equal. A big determiner in how long a flight will take is how big a boost the spacecraft gets from its Jupiter flyby. So we'd have to fit the timing to three planets: Earth, Jupiter and Orcus, and we might need to wait years for them to align properly. Also, nothing much is going to happen on Orcus for a century or so, so IMO a bigger priority would be Eris or Sedna. — kwami (talk) 04:23, 11 November 2021 (UTC)

Move discussion in progress

There is a move discussion in progress on Talk:90377 Sedna which affects this page. Please participate on that page and not in this talk page section. Thank you. —RMCD bot 20:00, 14 November 2022 (UTC)

Dwarf planet or not

I tagged this sentence as failed verification: Orcus had been accepted by many astronomers as a dwarf planet, though as of 2024 that consensus has changed.[2]

@Double sharp: responded: See below - they argue that Sedna, Gonggong, Quaoar differ from "all smaller TNOs" (which would include Orcus) in ways that imply they have undergone chemical evolution while the smaller ones have not, which is the point of the DP category

I read the paper before I tagged it for failed verification, I assume you were talking about this sentence: We suggest that these three bodies have undergone internal melting and geochemical evolution similar to the larger dwarf planets and distinct from all smaller KBOs. To nitpick, the underlined part doesn't logically imply that all smaller KBOs are definitely not dwarf planets. The rest of the text more or less puts Sedna, Gonggong and Quaoar in a third group different from both larger bodies and undiscussed smaller bodies (no evidence of neither methane nor methanol).

Not being listed in a single paper specifically focusing on chemical composition of three unrelated dwarf planet candidates to me isn't enough of a development to belong right in the third sentence for Orcus. Especially since the Dwarf planet article goes on and on about how there's no consensus on which TNOs are dwarf planets (There is no clear definition of what constitutes a dwarf planet, and whether to classify an object as one is up to individual astronomers). IvicaInsomniac (talk) 21:40, 13 March 2024 (UTC)

@Kwamikagami: Pinging you for your opinion. Double sharp (talk) 03:02, 14 March 2024 (UTC)

Also Exoplanetaryscience. Double sharp (talk) 03:03, 14 March 2024 (UTC)

I thought we had two papers now that said this: Quaoar up look geologically active (or at least formerly so); the rest do not. The fact that they don't specifically mention Orcus is no more reason to ignore their claim than their similar failure to mention Salacia, Varuna, Ixion, etc. — kwami (talk) 07:04, 14 March 2024 (UTC)

BTW, the relevant passage is "We suggest that Sedna, Gonggong, and Quaoar all underwent internal melting, differentiation, and chemical evolution, similar to the larger dwarf planets and distinct from all smaller KBOs." — kwami (talk) 23:12, 24 May 2024 (UTC)

@Kwamikagami in case it is missed (and because it is directly relevant), Ardenau4 noted that the currently measured size of Orcus is consistent with Quaoar's and Sedna's, not smaller. AstroChara (talk) 19:09, 15 March 2024 (UTC)

Smaller than Quaoar to more than 1 sigma. Overlaps with Sedna. — kwami (talk) 02:16, 16 March 2024 (UTC)

Revisiting this topic after a while. Though I do agree that Orcus's status as an unambiguous dwarf planet is on shaky ground, and really hasn't much of a better justification than Salacia and Varuna, I must agree here that the paper provided is pretty weak in arguing against Orcus's classification, especially for it to warrant declaring that 'consensus' has swung against it. To my knowledge, it has not; as recently as just last year, some astronomers have been referring to Orcus as a dwarf planet. One paper does not change consensus; this would arguably be an example of undue weight.

I would suggest citing additional papers such as Fornasier et al., where the authors do not refer to Orcus as a dwarf planet, to more clearly demonstrate that consensus does not (and perhaps arguably never has) favor Orcus as a dwarf planet, and that opinion is still divided. ArkHyena (talk) 21:34, 14 March 2024 (UTC)

The above source does not really seem helpful, given that it does not refer to Quaoar as a dwarf planet as well. Rather, it seems more likely that the above paper intends to discuss TNOs as a whole and to not make distinctions between dwarf planets and non-dwarf planets. I also should mention that, actually, from the most recent size estimates, Sedna is slightly smaller than Orcus (but the sizes are essentially identical given the large uncertainties). It's not clear that "all smaller TNOs" should refer to Orcus, considering that Orcus is in the same size range as Quaoar and Sedna, whereas Varuna, 2002MS4, etc. are clearly smaller. Salacia once again falls within a grey area, but Salacia has not been in the list of "consensus dwarf planets" for a while now. Given this does not really make sense to say that the consensus has "changed". Ardenau4 (talk) 21:45, 14 March 2024 (UTC)

Coming back to additionally note that Grundy et al. 2019 seems to provide the actual justifications as to why most astronomers classify Orcus as a dwarf planet:

Orcus and Charon probably melted and differentiated, considering their higher densities and spectra indicating surfaces made of relatively clean H2O ice. But the lower albedos and densities of Gǃkúnǁ'hòmdímà, 55637, Varda, and Salacia suggest that they never did differentiate, or if they did, it was only in their deep interiors, not a complete melting and overturning that involved the surface.

Combined with the above, I believe that removing Orcus from the list of consensus dwarf planets here was premature. ArkHyena (talk) 17:40, 16 March 2024 (UTC)

Grundy is a co-author of the latest paper. But it's true that we don't know that he (or his 2019 co-authors, none of whom were authors of the 2023 papers) agree with this particular statement. I've seen papers on what is a planet that effectively concluded that Earth and Jupiter are not planets, which I'm pretty sure are not conclusions shared by any of the authors. (Though much more sloppily written than this one, the point is that legalistic reading of a paper may be justified when there is a single author, who we know to be precise in their writing, but not when there are several.) So maybe it was premature. — kwami (talk) 18:05, 16 March 2024 (UTC)

BTW, the paper in question had both Stern and Grundy as co-authors, among others, but I suspect they didn't have much if anything to do with writing it, and instead signed on to something they agreed with to help make a point. It was an opinion piece that dwarf planets should be considered planets and had no real academic content. But my point is that it defined one criterion for planethood as being a tri-axial spheroid. Since that is a mathematical impossibility, a legalistic reading is that there is no such thing as a planet. Obviously, none of the authors intended what it said. I think it's quite possible that if you asked the authors of the 2023 paper about Orcus, they'd hedge, and of course we don't know about Noll or Buie etc. from the 2019 paper. — kwami (talk) 18:27, 16 March 2024 (UTC)

The point is that if it's really the case (per the 2023 paper) that Sedna, Gonggong, and Quaoar differ from "all smaller TNOs" (which would rather include Orcus under current size estimates) in whether or not they are chemically evolved, then the conclusion of the 2019 paper about Orcus is not so clear anymore. And it was specifically only a "probable" thing anyway, considering that by the 2019 criteria, Orcus has the albedo but is on the borderline for density. So I think it makes sense to consider Orcus somewhat unclear, but one step more likely than Salacia. It might take a while for a detailed study of Orcus to settle it, of course. Double sharp (talk) 04:04, 18 March 2024 (UTC)

We do have a gradient of probability, which is lost when we give a specific list. Also, Vesta is chemically evolved, but we don't consider it a DP. — kwami (talk) 04:43, 18 March 2024 (UTC)

That is largely due to it significantly departing from an ellipsoidal shape; if it weren't for the Rheasilvia and Veneia impacts, we would likely be identifying Vesta as a DP. Orcus may or may not be significantly out of HE, especially since 2002 MS4 demonstrates objects larger than Vesta can similarly be knocked out of HE from impacts, but then again 2002 MS4 does not appear be (as) chemically evolved like Orcus is.

Double sharp is correct though in that Orcus's properties are quite poorly known. The justification for calling Orcus a DP largely appears to come from how Charon, arguably the most similar known object to Orcus, is very clearly of planetary nature and has sustained its own extensive geological history. This, of course, is a tentative justification though. ArkHyena (talk) 05:00, 18 March 2024 (UTC)

When the IAU was discussing the DP concept in 2006 (i.e. before Dawn), Vesta, Pallas, and Hygiea were all considered candidates. So I agree with ArkHyena that Vesta without impacts would certainly be considered a dwarf. Proteus is in a similar situation, and would probably be classed as a planemo moon if its surface features had relaxed. OTOH, there's clearly some limit, as Iapetus is generally included despite the equatorial ridge.

Charon is probably significantly larger than Orcus and orbits the largest current DP. Anyway, extrapolating from what is known will always have problems: in the past, the general consensus based on Mimas and Enceladus was that icy objects that size should generally be geologically evolved, and look how that turned out. :) Probably the best way to describe Orcus at present is to say that it's often included among DPs, but that there is some evidence that it might not be one. The current wording seems fine to me. Double sharp (talk) 06:37, 18 March 2024 (UTC)

The current wording makes it sound a lot like something was majorly changed in 2023, specially since it cites a 2023/4 source, and I see we can't even be 100% positive this source intends to judge Orcus's status. Wouldn't it be better to just move the details down to "Size and magnitude" where the other dwarf planet - not dwarf planet judgements are and then shorten them into that sentence at the top of the article? IvicaInsomniac (talk) 00:49, 19 March 2024 (UTC)

I can see how linking it to just one source could imply that, though this is complicated by how very few papers appear to ever discuss/debate Orcus's possible DP status head-on, and instead typically lump it in with other objects. And indeed, a better-written section on Orcus's status and its relationship compared to other large TNOs would be warranted; looking over Orcus's article as a whole, a touch-up looks needed anyways. ArkHyena (talk) 23:21, 10 April 2024 (UTC)

The Consensus Is That Orcus Is Still A Dwarf Planet

@Double sharp has edited this page was well as other pages mentioning Orcus to remove any mentions of there being an established consensus among astronomers confirming Orcus's dwarf planet status. (The other pages edited by Double sharp include Solar System, Timeline of discovery of Solar System planets and their moons, Dwarf Planet, List of possible dwarf planets, and List of gravitationally rounded objects of the Solar System. Double sharp also edited Template:Solar System, but this edit was partially reverted by @ArkHyena. Interestingly, Double sharp did not remove Orcus from the chart on Clearing the neighbourhood, but this may have just been an oversight.) This was primarily due to the release of Emory et alii's study. I think, however, it was premature to make these edits for the following reasons.

1. Orcus's estimated diameter of 910+50
−40 kilometers is larger than Sedna's 906+314
−258 kilometers. (Sedna was the smallest dwarf planet analyzed in the study.) In fact, even if we took the lowermost end of the range for Orcus, 870 kilometers, it would still be larger than the lowermost end for Sedna, 648 kilometers. Therefore, it is safe to say that Orcus is easily within the size range of the three dwarf planets mentioned by the study, (Gònggōng, Quaoar, and Sedna). So, it's not accurate to classify Orcus as being one of the "smaller KBOs" alluded to by the sentence, "We suggest that these three bodies have undergone internal melting and geochemical evolution similar to the larger dwarf planets and distinct from all smaller KBOs," in the study.

2. As @IvicaInsomniac pointed out, Orcus not being mentioned in the study does not mean the authors were implying it's not a dwarf planet. It would be like saying a study analyzing all of the planets except for Mercury must somehow be implying Mercury is not actually a planet. @Kwamikagami has brought the point that one go even further with this to imply that possible dwarf planet candidates may also not be ruled out from not being mentioned in the study. However, unlike Orcus, those candidates do not have any consensus surrounding them, while Orcus does.

3. Even if Orcus were smaller than Sedna, the study in question, as pointed out by IvicaInsomniac, does not state that celestial bodies smaller than the three dwarf planets analyzed are not dwarf planets.

4. The argument that Orcus's density is "too close" to the borderline dividing dwarf planets from what would essentially be large, slightly rounded asteroids has been brought up by Double sharp. However, every one of the studies that analyzed density to determine dwarf planet status all ultimately determined that Orcus does indeed meet the threshold. Scientific consensus among astronomers should take precedent over our personal interpretations of the data, no matter how valid they may be. (After all, Wikipedia is about following, not leading.)

5. The argument that Salacia is more or less in the "same grey area" as Orcus when it comes to having a similar size, density, and albedo has also been brought up by Double sharp. However, unlike Orcus, no consensus was ever formed about Salacia's possible dwarf planet status, (as @Ardenau4 pointed out, astronomers seem to currently be split on this), which is very different from Double sharp's argument that the consensus regarding Orcus's status has changed.

I propose reverting Double sharp's edits to how things to how things were before, including the other articles. (No offense to Double sharp, by the way. Sorry if I seem too harsh with this, lol.) Additionally, I propose modifying the chart on List of possible dwarf planets to change the yellow question mark for Orcus under the new study to a green checkmark with perhaps a footnote attached stating something along the lines of, "Not explicitly analyzed nor mentioned, but in the same size range of the dwarf planets evaluated." Alternatively, since, as I talked about above, the study does not state that celestial bodies smaller than the three dwarf planets it analyzed have not undergone the geochemical evolution "necessary" to be a dwarf planet, it might be better to remove that study from the chart entirely and just keep the other three. Unlike the other three studies, the study in question is simply not about determining dwarf planet status. Star VV Cephei A (talk) 21:43, 23 May 2024 (UTC)

Addendum

Double sharp's edits cause further complications.

Should the italicized sentence at the topic of the article for the Roman god Orcus be changed from saying Orcus is a "dwarf planet" to a "likely dwarf planet"? Or, perhaps a "possible dwarf planet candidate"?

Should the simple English article on Orcus be modified as well? What about the simple English dwarf planet article? What about how articles in other languages still call Orcus a dwarf planet?

Orcus is in the top left corner of this image with the other dwarf planets.

And how about these three images prominently displayed in the Solar System and planet articles that show Orcus as one of the nine consensus dwarf planets?

Orcus is once again in the top left.

And again.

With all due respect, I think Double sharp jumped the gun here. Star VV Cephei A (talk) 00:56, 24 May 2024 (UTC)

Other wikipedis can handle their own material. That's not our job, and not reason for us to be inaccurate. Likewise, needing to update graphics is not a reason to be inaccurate. I don't see how your arguments have anything to do with the issue at hand.

BTW, the term "candidate" is not accurate. They're only 'candidates' for someone's list, not for what they are. When we find a crater that we think might be volcanic, we don't say it's a 'candidate' volcano, but rather a 'possible' or 'likely' [etc.] volcano. I think we should do the same here. — kwami (talk) 01:59, 24 May 2024 (UTC)

Fair enough on your point about the graphics, but what do you think of the five points I listed? (Scroll above.) Star VV Cephei A (talk) 03:51, 24 May 2024 (UTC)

I agree that the change was extremely premature. We got the general sense in the literature that Orcus was among the large bodies considered very likely to be dwarf planets (unlike Salacia), but the statement in Emery et al. that seemed to have prompted the change in how we refer to Orcus on Wikipedia seems to come from the second page, with the authors stating:

"We suggest that these three bodies [Gonggong, Quaoar, and Sedna] have undergone internal melting and geochemical evolution similar to the larger dwarf planets and distinct from all smaller KBOs."

Orcus is not a smaller KBO. The best fit size for Orcus is larger than that of Sedna, and the two are equal within measurement uncertainties. The above statement in Emery et al. never intended to refer to Orcus in the first place. Given this in mind, to suggest that the consensus has "changed" in our articles is extremely premature and improper. Ardenau4 (talk) 04:10, 24 May 2024 (UTC)

Exactly! Do you happen to have any thoughts on the other four points I listed? Star VV Cephei A (talk) 04:32, 24 May 2024 (UTC)

From what I've seen, it's pretty well-established in literature that Orcus is generally considered at least a "likely" dwarf planet by astronomers and, as per Ardenau4's statement in an earlier discussion: Given this does not really make sense to say that the consensus has "changed" (referring to the implications of Emery and collaborators' paper). Whether or not to include it in Wikipedia's roster of dwarf planets is more difficult to say, since that implies a binary that dwarf planet candidates of course don't follow nor care about. Orcus is a very poorly-studied object, for example, so it may end up not being planetary in nature after all come future observations (though keep in mind WP:NOTCRYSTAL).

Personally, I would argue for its inclusion (with the caveat that its status is more uncertain than the other eight "consensus" DPs) since there is little indication that consensus has changed or that Emery et al.'s statement applies to Orcus. ArkHyena (talk) 04:11, 24 May 2024 (UTC)

As to your point about how many astronomers use the word likely when referring to Orcus, they also often use that same word when talking about Gònggōng, Quaoar, and Sedna since they are not among the I.A.U.'s "big five". While it's true Orcus's nature is not as understood as well as some of the others, it still qualified according each of the three other studies we're using to determine dwarf planet status. Do you also happen to have any thoughts pertaining to any of the five points I listed? Star VV Cephei A (talk) 04:31, 24 May 2024 (UTC)

There still is a greater level of uncertainty surrounding Orcus's status from what I've seen in literature; this makes sense, seeing as Orcus (and Sedna) are smaller than Quaoar and Gonggong, and how the conclusions by Emery and collaborators very strongly support the notion that Sedna, Gonggong, and Quaoar are planetary in nature (with Orcus crucially being outside the paper's scope). This is an important caveat I believe should be mentioned, especially if we do add Orcus back to the list here. ArkHyena (talk) 04:39, 24 May 2024 (UTC)

I suppose I should explain myself. The main reason I made the changes in the first place was that the line we tended to use for DPs is between (1) those which nobody doubts, like Quaoar, and (2) those that might be, but aren't very clear, like Varda. All of them are discussed in places like list of possible dwarf planets, but you wouldn't use Varda (say) as an exemplar right off the bat the way you could use Quaoar. Since Orcus wasn't mentioned in the new study, and it was already kind of suspicious (its density is borderline), it seemed doubtful enough to move from the bottom of (1) to the top of (2). My logic thus is that the objects we list as the standard DP exemplars really ought to be the ones nobody actually doubts.

Also, the thing that makes Sedna, Gonggong, and Quaoar probably DPs in the new study is finding a significant abundance of light hydrocarbons on the surface: that suggests differentiation (for a continuous renewal of them), and is absent from smaller TNOs. These have not been found for Orcus, despite the fact that spectroscopic observations have been done (see 90482 Orcus#Spectra and surface): future studies may yet identify them, but the fact that they haven't been found yet suggests that the abundance might actually be intrinsically low. Kind of SYNTH though, I admit.

It's true that I made the changes before more detailed studies on Orcus came out. So arguably I jumped the gun, and I'm fine with reinstating it for now. I'll still privately bet against it, though. ;) Double sharp (talk) 12:20, 24 May 2024 (UTC)

I think that if the newest and best studies leave out Orcus, then we should too. Salacia is also borderline in the sources, but borderline isn't consensus. — kwami (talk) 15:01, 24 May 2024 (UTC)

The study not mentioning Orcus is not the same thing as saying Orcus is not a dwarf planet. (See point number two in my list above.) The study itself isn't even about determining what does and doesn't qualify as a dwarf planet. It ultimately makes no statements contradicting the current consensus concerning Orcus's dwarf planet status. As for Salacia, see points four and five in my list above. Star VV Cephei A (talk) 15:07, 24 May 2024 (UTC)

I remain unconvinced that one single study (which, as aforementioned, is not even concerned with whether or not Orcus is planetary in nature) is grounds enough to leave out Orcus. Conversely, a recent 2024 source by G. Leone and Tanaka H. (which is open-access under CC 4.0) explicitly outlines the differences between Orcus and Salacia. Quoting: Although the sizes of Orcus and Salacia are almost similar, their densities are quite different thus implying a higher rocky fraction in the core and/or a thinner mantle within Orcus.; Also, the thermal evolution of Orcus shows some differences with Salacia; although the general trend is similar, a higher peak temperature of 900 K was reached 400 Ma after Salacia... and If the modeling is correct, ongoing cryovolcanic activity should be expected and possibly detected on Orcus. The detection of crystalline ice, along with methane and ammonia ice, on the surface of Orcus161,164,167 is consistent with possible cryovolcanic processes...

So now we have at least some work done that explicitly supports Orcus as a more thermally evolved body than Salacia, and that it itself may support cryovolcanism based on modelling (though note that the modelling referenced in the paper is a pre-NH paper). ArkHyena (talk) 22:56, 24 May 2024 (UTC)

Except that uses a dated estimate for Salacia's density. Back it 2015 it was thought that there was a difference; current estimates have Salacia nominally denser than Orcus. The most recent study excludes Orcus. — kwami (talk) 23:04, 24 May 2024 (UTC)

Though true, if the discrepancy is with Salacia's density, the consequences of that would primarily affect our interpretations of Salacia and not Orcus, would it not? Whether it will affect astronomers' perception of Salacia's nature (and importantly, if it will have any effect on interpretations of Orcus) has yet to be seen in literature, and does not apply to Orcus. Furthermore, as stated before by Star VV Cephei A, Ardenau4, and I; the Emery et al. paper does not concern Orcus's planetary status. ArkHyena (talk) 23:11, 24 May 2024 (UTC)

It means that your reference is not relevant. We're back to the original paper. — kwami (talk) 23:15, 24 May 2024 (UTC)

This recent paper clearly refers to Orcus as a dwarf planet, and not Salacia, so I think it clearly matters here. The Tales of the Three Dwarf Planets paper, on the other hand, does not say anything about Orcus's dwarf planet status. AstroChara (talk) 23:22, 24 May 2024 (UTC)

It doesn't negate all of the reference. Concerning modelling of Orcus's interior and how it may relate to cryovolcanism: that still likely applies, providing that post-NH data does not somehow imply that Charon-sized objects are worse at generating or retaining internal heat than expected. Secondly, the statement connecting the probable detection of certain ices on Orcus relating to possible past cryovolcanic activity also still applies; as far as I can tell, no subsequent work has refuted the presence of surface methane or ammonia ice on Orcus. This is still a relevant paper.

Importantly, this is still an example of a recent article explicitly labelling and treating Orcus as a dwarf planet. ArkHyena (talk) 23:25, 24 May 2024 (UTC)

FWIW, I'm convinced by this paper that I jumped the gun, and that Orcus should be reinstated. I'm currently travelling; if no one beats me to it, I'll probably start putting it back in the next couple of days. Double sharp (talk) 05:13, 25 May 2024 (UTC)

But it's based on old data. No actual research. The claim that it's a DP dates from 2016, and the density estimate from 2015. Our only recent ref is the one you found. — kwami (talk) 07:04, 25 May 2024 (UTC)

To my understanding, the situation on Orcus is similar to Haumea, which is undoubtedly a dwarf planet, and Charon, which is basically one, so I don't believe you can use that to justify Orcus not being a dwarf planet. And as OP said, nowhere in the paper itself do the authors claim that the presence of light hydrocarbons separate dwarf planet from asteroids. AstroChara (talk) 17:06, 24 May 2024 (UTC)

Similar how? — kwami (talk) 23:14, 24 May 2024 (UTC)

Their spectra all show surfaces full of water ice, with little light hydrocarbon. AstroChara (talk) 23:49, 24 May 2024 (UTC)

Requested move 14 June 2024

The following is a closed discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. Editors desiring to contest the closing decision should consider a move review after discussing it on the closer's talk page. No further edits should be made to this discussion.

The result of the move request was: moved. (non-admin closure) Safari Scribe^{Edits! Talk!} 04:53, 22 June 2024 (UTC)

---

90482 Orcus → Orcus (dwarf planet), and include it in Wikipedia:Featured topics/Dwarf planets – To maintain consistency, per WP:TITLECON. The recent discussion at Talk:Sedna (dwarf planet) has established that Sedna, Gonggong and Quaoar are considered dwarf planets by the established scientific consensus, and those articles were moved accordingly. There is no qualitative difference between the situation for those objects and Orcus. Orcus was mentioned in the discussion at Sedna, but was purposefully left out (for reasons explained below) so it can be discussed here separately. Now is the time to do that.

Wikipedia does not follow the IAU's position when it comes to determining which objects are considered dwarf planets in the scientific literature. Rather, Wikipedia:Naming conventions (astronomical objects)#Dwarf planets now asks for objects to be included in Wikipedia:Featured topics/Dwarf planets before they are titled as such. The purpose of this, as explained here, is to ensure that a thorough discussion has taken place whether there is sufficient scientific consensus, thus ensuring a stable basis for what objects we consider to be dwarf planets. This is currently the case for the eight objects on the featured topic. It also appears that Orcus is the only other object that may currently qualify to be added to that list. The Orcus article itself of course treats Orcus as a dwarf planet, and has done so for quite some time.

The reason why Orcus was left out of the recent move request is that its status was unclear: Orcus had been added to that featured topic in early 2024,[3] but this was challenged in May.[4] As a good article, Orcus is technically eligible to be on that list. Its removal sparked the discussion at Talk:90482 Orcus#Dwarf planet or not, which was followed up by Talk:90482 Orcus#The Consensus Is That Orcus Is Still A Dwarf Planet. The arguments for and against a possible move have been outlined, and I point there for further details, but the arguments in favour of considering Orcus a dwarf planet are basically the same as in the move request for Sedna, Gonggong and Quaoar. While there were some opposing views (as there were in the successful move request for the other three objects), the arguments against were basically the same, too.

To maintain consistency, I believe that Orcus should therefore be included in the featured topic, and the article should be titled accordingly. Renerpho (talk) 11:51, 14 June 2024 (UTC)

Notified: WikiProject Astronomy. Renerpho (talk) 11:54, 14 June 2024 (UTC) Igordebraga has been contacted about their reason to have previously removed Orcus from the featured topics list. Renerpho (talk) 16:01, 14 June 2024 (UTC)

• Support per nom, in addition to my own reasoning for proposing the aforementioned moves in Talk:Sedna_(dwarf_planet)#Requested_move_6_June_2024. Comment: Seeing as Orcus has yet to be re-included into Wikipedia:Featured topics/Dwarf planets, I believe there should be a parallel (or at least subsequent) discussion to re-include it. ArkHyena (talk) 15:30, 14 June 2024 (UTC)

There should be a parallel (or at least subsequent) discussion -- I suggest a parallel discussion. The two questions are directly linked. I have amended the proposal accordingly, requesting not only to move the article, but also to include it in the featured topics list. Comment Just for reference, I'd like to point out that Igordebraga's removal of Orcus from the featured topics list was based on a comment by ArkHyena during its FTC in April.[5] Renerpho (talk) 16:15, 14 June 2024 (UTC)

• Support, the nomination seems to have covered all the bases. Randy Kryn (talk) 03:23, 15 June 2024 (UTC)
• Support: a search starting with the name seems more likely than one using the minor planet number. Praemonitus (talk) 14:56, 15 June 2024 (UTC)
• Support as the reasons given by Praemonitus seem reasonable to me. 21 Andromedae (talk) 15:33, 16 June 2024 (UTC)

Support: I completely agree, the reasons seem reasonable, and it'd create an easier way to search for this fascinating body on browsers. 192.180.36.129 (talk) 00:01, 17 June 2024 (UTC)

Support as per nomination. AstroChara (talk) 22:22, 17 June 2024 (UTC)

Support, request has good reasons, I agree. LunaTheSilly (talk) 00:56, 20 June 2024 (UTC)

The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.