# Talk:Hydra (moon)

Minimum diameter is lower bound only, not an actual estimate. It is assumed from Hubble team announcement that Pluto is not expected to have any other satellites larger than 10 miles in diameter, which implies that only objects larger than this were detectable. kwami 21:02, 31 October 2005 (UTC)
Good. Thanks for fixing. 
I also just measured an orbital distance of 65Mm off the NASA system diagram. Is that how the data here was obtained? Has NASA not published a best-fit orbit? kwami 21:20, 31 October 2005 (UTC)

According to the Bad Astronomer[1] the smaller one is 100-140 km in diameter and the larger one is 110-160 km in diameter (which is which, I don't know). That blog has also the orbital distance values. The original press release is woefully void of any concrete values, and the discovery IAUC[2] is not available to non-subscribers.--Jyril 21:24, 31 October 2005 (UTC)
Ah, just found the discoverers' site: http://www.boulder.swri.edu/plutonews/ --Jyril 21:27, 31 October 2005 (UTC)
"The smaller one" is presumably P2, which I have just noted. Having the broadest possible range for diameter as it now stands makes the most sense. Marskell 11:00, 3 November 2005 (UTC)

One of the discovery team's publications (ref'd around here somewhere) states that P1 is the brighter (outer) moon. This is assumed to be the larger as well. One of our articles had it backwards for a while.
A 3-fold range in size makes sense with a 10-fold range in albedo, so I believe you're correct with the diameter guestimates.
kwami 11:09, 3 November 2005 (UTC)

A claim's been made that the name Cerberus (Pluto's three-headed dog) has been proposed for Pluto III. No refs, but just in case, the pronunciation's sur'-bər-əs, Greek Κέρβερος. kwami 01:23, 4 November 2005 (UTC)

Surely in the original latin pronunciation, the first c would always be pronounced as a hard c - similar to how we'd prounounce a k. Pronouncing the first c as an s-sound would be very anglicised. Pronouncing it as a hard c would clearly match the greek, who used kappa as their first letter. Richard B 15:00 21 November 2005 (UTC)
Here is the ref from Latin pronunciation
C  /k/  (as in skate, never like c in piece) Richard B 15:16 21 November 2005 (UTC)
But this is English Wikipedia, not Latin. Besides, in modern Latin, the c would either be like English ch or s. Anyway, that's what the Greek is for: Anyone who wishes to pronounce the name in Latin or Greek can do so. kwami 01:53, 22 November 2005 (UTC)
I like these names.  I made a table of the satellites named.  Check this out.  — Hurricane Devon (Talk) 13:34, 5 December 2005 (UTC)
Yes, all the names of moons, planets, and constellations have anglicized pronunciations. Nobody would understand you if you pronounced Venus as "WAY-noose" /'weːnʊs/. QuartierLatin1968  23:03, 21 January 2006 (UTC)

It seems like this article, and S/2005 P 2 are almost identical to each other. Wouldn't it be better to merge the two? 65.92.150.128 21:21, 21 January 2006 (UTC)

We don't do that for any of the other moons. And when they're named, we'd have an article named something like "Cerberus and Orthrus (moons)". kwami 22:31, 21 January 2006 (UTC)
I wouldn't support merging either. True, not much may be known about the one that isn't known about the other – but that is certain to change as more is learnt about trans-Neptunian objects. QuartierLatin1968  23:00, 21 January 2006 (UTC)
Every planetary satellite has its own article. Let it stay so.--Jyril 00:00, 22 January 2006 (UTC)

It is thought that this near-resonance may be the result of a periodic local fluctuation of 15% in the Pluto-Charon gravitational field. What does "periodic local fluctuation of the gravitational field" mean?  How can a gravitation field change? Nik42 07:24, 25 February 2006 (UTC)

The combined gravitational field of Pluto and Charon is not symmetrical. It changes when they orbit each other. So I've understood it.--Jyril 08:42, 25 February 2006 (UTC)
There is a strong dipole effect. The Pluto-Charon distance is 19.571 Mm, and the mass ratio 8.59 (which means Pluto accounts for 89.6% of the mass, Charon for the rest), so the Pluto-barycentre distance is 2.042 Mm whilst the Charon-barycentre distance is 17.529 Mm. The strongest gravitational pull is in the Pluto-Charon-moonlet alignment case, the weakest when the moonlet is 90° from the Pluto-Charon axis.
Pluto-Charon-Nix alignment:
Nix semi-major axis (Nix-barycentre distance): 48.675 Mm
(Normally the semi-major axis would be the Nix-Pluto distance, but the Pluto-Charon barycentric distance is what is reported in the litterature; Nix's small mass induces a distance correction of between 7 and 0.2 km (9 and 0.2 km for Hydra), so we neglect that here)
Pluto-Nix distance 48.675+2.042 = 50.717 Mm, M/r² value is 5.074 Gg/m²
Charon-Nix distance 48.675-17.530 = 31.146 Mm, M/r² value is 1.567 Gg/m², total 6.640 Gg/m²
Pluto-Charon-Nix quadrature:
Pluto-Nix distance sqroot(48.675²+2.042²) = 48.718 Mm, M/r² value is 5.498 Gg/m²
Charon-Nix distance sqroot(48.675²+17.530²) = 51.735 Mm, M/r² value is 0.568 Gg/m², total 6.066 Gg/m²
The ratio is 6.640/6.066 = 1.095

Pluto-Charon-Hydra alignment:
Hydra semi-major axis (Hydra-barycentre distance): 64.780 Mm
Pluto-Hydra distance 64.780+2.042 = 66.822 Mm, M/r² value is 2.923 Gg/m²
Charon-Hydra distance 64.780-17.530 = 47.251 Mm, M/r² value is 0.681 Gg/m², total 3.603 Gg/m²
Pluto-Charon-Hydra quadrature:
Pluto-Hydra distance sqroot(64.780²+2.042²) = 64.812 Mm, M/r² value is 3.107 Gg/m²
Charon-Hydra distance sqroot(64.780²+17.530²) = 67.110 Mm, M/r² value is 0.337 Gg/m², total 3.444 Gg/m²
The ratio is 3.603/3.444 = 1.046
Urhixidur 14:29, 28 May 2007 (UTC)

... the moon is calculated have a diameter of between 44-50 km, if its reflectivity is similar to Charon's 35%, and 130-150 km, if it has a reflectivity of 4% like the darkest KBOs. All of Pluto's moons are spectrally neutral, however, so the lower end of the range seems likely. 
Lower end of radius or albedo range? (same applies to S/2005 P 2) Deuar 14:45, 28 May 2006 (UTC)

Science magazine reports that S/2005 P 1 will be called "Hydra". [3]  This article should presumably be moved to Hydra (moon), but I suppose it is appropriate to wait until the official announcement on June 23.

Yeah, better to wait for the official announcement.--JyriL talk 13:50, 21 June 2006 (UTC)
The offical annoucement is moot since they've already offically annouced what they intend on naming the moons during their redundent offical annoucement.  If that made any sene.  Anywho, I tried to change the titles without logging on in an apparently unelegent name (cut and paste).  I'm not going to move the article as someone suggested. Lou.nunez 09:42, 22 June 2006 (UTC)

S/2005 P 1 → Hydra (moon) … Rationale: To reflect the the new offical name for Pluto III.  BTW I tired doing it myself and I just seemed to screw things up.   Please share your opinion at Talk:Hydra (moon). Lou.nunez 09:58, 22 June 2006 (UTC)


### Survey
Add *Support or *Oppose followed by an optional one-sentence explanation, then sign your opinion with ~~~~
Support  It's the official name of the moon, so that ought to be reflected.  --DavidK93 14:03, 22 June 2006 (UTC)
Support In my mind, this process shouldn't even need to be voted on... Tuvas 19:03, 22 June 2006 (UTC)
Strong support as above. --GW_Simulations|User Page | Talk | Contribs | E-mail 19:10, 22 June 2006 (UTC)
Strongly support as above. Tom Temprotran 22:45, 22 June 2006 (UTC)
Support It's official now, so it's a simple case closed to me. -- Northgrove 23:55, 22 June 2006 (UTC)
Strongly support as above. Chaos syndrome 10:18, 23 June 2006 (UTC)
Comment It's probly the right move, but maybe not directly in line with policy. As far as I know, researchers aren't using the name yet (for example, I looked up the article after a collaborator of mine said they'd named P1 & P2, though he couldn't recall what they named them.  Are P1&P2 far enough into the public consciousness that the terms are widely used?WilyD 14:24, 23 June 2006 (UTC)
Since this is all over the news (try google-news-searching "Hydra Nix") I think that the general public now thinks of these moons as Nix and Hydra, and I'd expect the scientific establishment to follow quickly. DenisMoskowitz 14:27, 23 June 2006 (UTC)
Okay, I buy it.  Besides, if the general public uses the term, it should trump the scientific community's standards anyhow. WilyD 15:42, 23 June 2006 (UTC)
Good point. I mean, who uses the term Dihydrate Monoxide, instead of it's common term, water? Tuvas 17:53, 23 June 2006 (UTC)
Support WilyD 15:42, 23 June 2006 (UTC)
Strong support IAUC 8723 - 'nuff said. Urhixidur 14:30, 23 June 2006 (UTC)


### Discussion
Add any additional comments
Really, this should be done on the talk page for the existing article (ie. talk:S/2005 P 1) GW_Simulations|User Page | Talk | Contribs | E-mail 19:10, 22 June 2006 (UTC)

Merged. Ian¹³/t 19:03, 23 June 2006 (UTC)
Done. Ian¹³/t 19:03, 23 June 2006 (UTC)

I have fixed any double redirects, but links to the wrong page in articles and templates and the like still need to be updated (preferably by someone who knows these articles well). Ian¹³/t 19:04, 23 June 2006 (UTC)
I did a few of them that were obviously OK to switch, working from the bottom of P2's "what links here" page. DenisMoskowitz 19:23, 23 June 2006 (UTC)
I got carried away and did the rest of them.  Didn't touch user pages, talk pages, the Requested Moves page, and the pages P and S where the designation itself was used as an example. DenisMoskowitz 19:50, 23 June 2006 (UTC)
Sounds sensible, and that you have done all the right ones. Many thanks. Ian¹³/t 19:21, 24 June 2006 (UTC)

This statement in current version of the article is incorrect: It was named after Hydra, the monster who guarded Pluto's underworld in Greek mythology. The mythological Hydra did not guard the underworld, that was Kerberos (Cerebrus). Reference should be to the monster which features in the legends of Herakles (Hercules) as the referenced article on the mythological Hydra correctly details.

Actually there was a hydra that that guarded the underwold. It lived under the waters of the underworld. I don't remember what body of water this was...if it was the Styx, the Lethe or Menemosyne or something all together different. But a hydra did guard the underworld. I have edited the page to reflect this. (As a side note, it is possible that the hydra guarding the "underworld" could be an early creation, a water creature that hides in the under the water, before the underworld was an actual realm. I don't know, just trying to think of possibilites of where this came from...but I know this myth exists somewhere.) Jupiterzguy 03:11, 29 August 2006 (UTC)
Okay, I think I figured it out. The original Hydra myth featured the hydra that lived in waters so deep and dark it was said to be an entrance to the Underworld itself. This legend had apparently fallen out of common usage by the time of the Heracles myths, and the Hydra just guarded some random water body.Jupiterzguy 14:35, 14 September 2006 (UTC)
https://en.m.wikipedia.org/wiki/Wikipedia:WikiProject 70.173.179.7 (talk) 21:06, 22 February 2025 (UTC)
!! 70.173.179.7 (talk) 21:08, 22 February 2025 (UTC)

An official image should be released in a few minutes/hours/days. This one was captured from the NASA-TV live-stream.
LINK (not mine): http://i.imgur.com/pG7Ek8b.jpg
Damn thing looks like a chinchilla.....Ericl (talk) 13:22, 17 July 2015 (UTC)

An IP editor continues to swap out the processed picture with the pixelated one. I don't see the logic here, but the IP doesn't care to explain. So what image should be used? Dustin (talk) 22:18, 20 July 2015 (UTC)
It seems that an IPv6 (different from the one changing the images) left me a message on my talk page for when my main talk page is semi-protected but I didn't ever check it because my talk page is not currently semi-protected... Either way, this still needs to be discussed. Dustin (talk) 22:25, 20 July 2015 (UTC)

What on Earth is an "even rotational axis"? 89.12.202.104 (talk) 22:27, 12 September 2015 (UTC)

That's nothing (it's supposed to be a construction of the form "and even this", but I don't know why we should use that). Apparently, "rotational axis" is mentioned twice.  --JorisvS (talk) 22:58, 12 September 2015 (UTC)

The albedo figures for Hydra are inconsistent. The article states:
"Hydra's reflectivity (the percentage of incident light reflected from the surface) is intermediate between those of Pluto and Charon."
Pluto's albedo is 0.49-0.66 (geometric), that of Charon is 0.2-0.5.
"Albedo 0.83 ± 0.08 (geometric)"
This indicates an albedo significantly higher than Pluto's.
"Hydra's reflectivity is estimated to be about 45 percent."
This agrees with the earlier figure (between Pluto and Charon), but strongly disagrees with the latter.
Renerpho (talk) 15:45, 10 September 2017 (UTC)

Do we have any suggestion of where the so-called estimate of Hydra's mass has come from? It's very nearly the vaguest one I've seen on these pages, other than one of the two guesses for Nix. 4.8 ±4.2 x 10^16 kg essentially means "somewhere between 6 and 90 teratonnes... like... we don't really know..."; given that it's a 15:1 range, isn't it hardly any better than saying "no more than 9.0 x 10^16 kg"? I can only speculate that the lower and upper estimates for both volume and density were multiplied, than it was thought reasonable to take the average of the two results as a putative "actual" figure even though the error bars are humongous.
It's a bit like saying my own height is about 96cm, plus or minus 84cm - or 12 to 180cm - although the reality is right at the top end of that total range... or maybe 180cm, plus or minus 157cm (= 23 to 337cm...) ... or indeed if my size turned out to be right at the low end, 14.4m, plus/minus 12.6m... Whilst the middle one gives you a very rough range of how large a human might be, that covers fantasy giants right down to fairies and gnomes, well outside the actual extremes of giantism and dwarfism, and even all but the most premature of babies... 209.93.141.17 (talk) 02:06, 25 September 2017 (UTC)

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This review is transcluded from Talk:Hydra (moon)/GA1. The edit link for this section can be used to add comments to the review.
Reviewer: Jens Lallensack (talk · contribs) 14:59, 17 March 2019 (UTC)

Reading now. --Jens Lallensack (talk) 14:59, 17 March 2019 (UTC)

Hydra has a highly reflective surface caused by the presence of water ice. – Highly reflective compared to other plutonian moons? Otherwise, I would add "similar to other plutonian moons".
Compared to the reflectivities of Pluto and Charon, Hydra's reflectivity is intermediate, in between those of Pluto and Charon. – Last part of the sentence is repetitive.
The New Horizons team had suspected that Pluto might be accompanied with other moons – I would specify which moons were known at that point. Moons other than Charon?
accompanied with – "accompanied by" seems to be more standard
as "P1" and "P2", respectively by the discovery team – would add comma after "respectively"
similarly to how the Moon was thought to have formed from debris ejected by a large collision of Earth – this means the moon is no longer thought to be formed this way?
Link/explain "tidal evolution", "neutral spectrum", "downlinked"
In this case, Hydra along with the smaller moons of Pluto had migrated outwards with Charon into their current orbits around the Pluto-Charon barycenter. – "would have migrated"?
Hydra was thought to have formed from two smaller objects merging into one single object. – Again "was thought", so this is no longer the case?
and its shortest axis 30.9 km (19.2 mi) across – some verb missing?
The surface spectrum of Hydra is slightly bluish compared to the neutral surface spectrum of Nix – somewhat repetitive.
Hydra is the outermost moon of Pluto, orbiting beyond Kerberos. Similarly to all of Pluto's moons, Hydra's orbit is nearly circular and is coplanar to Charon's orbit; all of Pluto's moons have very low orbital inclinations to Pluto's equator. – needs source.
As a result of this "Laplace-like" 3-body resonance, it has conjunctions with Styx and Nix in a 5:3 ratio. – needs source.
with a timing discrepancy of 0.3%. A hypothesis explaining the near-resonance suggests that the resonance originated before the outward migration of Charon after the formation of all five known moons, and is maintained by the periodic local fluctuation of 5% in the Pluto–Charon gravitational field strength.[notes 1] – needs source.
Hydra's surface composition, reflectivity, and other basic physical properties were later performed by New Horizons during the flyby. – needs source
Derived from those images, Hydra was given the approximate size estimate of 55 km × 40 km (34 mi × 25 mi). – needs source.
Hydra's surface composition, reflectivity, and other basic physical properties were later performed – maybe "measured" instead of "performed"?
That's all. It seems you are through now with Pluto's moons? Congrats. --Jens Lallensack (talk) 15:25, 17 March 2019 (UTC)
All done. Nrco0e (talk) 18:20, 17 March 2019 (UTC)

@Nrco0e: Thanks, promoting now. I may have little time during the next weeks, but hopefully others will pick up your other two articles you listed (our problem is a chonic lack of reviewers). In any case, if you see an article by another author listed at GAN that interests you then please feel free to contribute a review, you have more than enough experience for doing this. --Jens Lallensack (talk) 20:01, 18 March 2019 (UTC)

This article is worth adding: Background Information Regarding Our Two Newly Discovered Satellites of Pluto Nrco0e (talk • contribs) 02:56, 26 October 2025 (UTC)