Talk:Timeline of discovery of Solar System planets and their moons

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"Discovery" in title?[edit]

Should this article and its history be moved to Timeline of natural satellite discovery? - Jeandré, 2004-05-02t10:15z

Or perhaps change it to "Timeline of solar system objects discovery" and include Uranus, Neptune, the first six or so asteroids, the first Centaur (2060 Chiron), the first trans-Neptunian object ((15760) 1992 QB1), the first Sedna (whatever we end up classifying it). -- Curps 21:50, 2 May 2004 (UTC)
I think if we move it there, people will be inclined to add a huge number of asteroids and or comets to it.. I thought the list of natural satellite discoveries was rather straightforward. I don't know what else a timeline of natural satellites could be... But then again, the more info the better. I'm just thinking that the list might expand to the point of being unweildy. -Patteroast 20:42, 3 May 2004 (UTC)
I agree with Patteroast, tho including Uranus and Neptune in the 2nd paragraph would be helpful. - Jeandré, 2004-05-04t18:36z

Date headings?[edit]

Can we include satellites discovered on the same date without repeating the date? Completely linked dates are formatted as per preferences, but partially linked or unlinked dates are shown in the format the contributor used.

Instead of

which I see as (not linked)

  • January 13, 1986 - Desdemona
  • January 13, 1986 - Rosalind
  • January 13, 1986 - Belinda
  • January 20, 1986 - Cordelia
  • January 20, 1986 - Ophelia


which I see (using the yyyy-mm-dd format) as (not linked)

  • 1986-01-13 — Desdemona, Rosalind, Belinda
  • 1986-01-20 — Cordelia, Ophelia

and which people who use the USA format (mmmm d, yyyy) see as (not linked)

  • January 13, 1986 — Desdemona, Rosalind, Belinda
  • January 13, 1986 — Cordelia, Ophelia

and which people who use the normal format (d mmmm yyyy) see as (not linked)

  • 13 January 1986 — Desdemona, Rosalind, Belinda
  • 13 January 1986 — Cordelia, Ophelia

Note that the year has to be linked for the preference to kick in. - Jeandré, 2004-05-04t18:36z

I would say just link all the dates, in every line.
The usual rule of linking only the first occurrence of a term really just applies to ordinary articles, which are paragraph-oriented and intended to be read from start to finish. For timeline pages or tabular data, where each line stands independently, we shouldn't compel the user to search backwards for the prior occurrence of the term to find a link. -- Curps 19:18, 4 May 2004 (UTC)
Whoopsie. Sorry, I'm not sure what I was thinking with the date links. The new system works much better. --Patteroast 01:38, 9 Jun 2004 (UTC)

Exact discovery dates[edit]

Discussion moved here from Talk:Phobos (moon). On that page, the exact dates of discovery of Phobos and Deimos were discussed.

Good work, Curps. Now, how about solving the mystery of Saturn's Atlas, Prometheus and Pandora?

Atlas: 1980 (< Nov 12) Richard J. Terrile / Voyager 1 IAUC 3539 (1980 nov 13) reports S/1980 S 28 (Atlas) second-hand. The best photo of Atlas is dated 1980 nov 12.

Prometheus: 1980 (< Oct 25) Stewart A. Collins (& D. Carlson?) / Voyager 1 IAUC 3532 (1980 oct 25) reports S/1980 S 26 (Pandora) and 27 (Prometheus) as "first observed mid-october".

Pandora: 1980 (< Oct 25) Stewart A. Collins / Voyager 1 (See Prometheus for sources)

The only other satellites I'm having a hard time pinning down is Neptune's Naiad through Galatea sequence (and accessorily Larissa and Proteus):

Naiad (S/1989 N 6) 1989 (< Sep 18) Richard J. Terrile / Voyager 2 IAUC 4867 (1989 sep 29) reports "25 frames over 11 d"

Thalassa (S/1989 N 5) 1989 (< Sep 18) Richard J. Terrile / Voyager 2 (See Naiad)

Despina (S/1989 N 3) 1989 (< Jul 28) Stephen P. Synnott / Voyager 2 IAUC 4824 (1989 aug 02) reports "10 frames over 5 d"

Galatea (S/1989 N 4) 1989 (< Jul 28) Stephen P. Synnott / Voyager 2 (See Despina)

Larissa (S/1989 N 2) 1981 (May 24) Harold J. Reitsema, William B. Hubbard, Larry A. Lebofsky & David J. Tholen (Science, vol. 215, Jan. 15, 1982, p. 289-291); 1989 (< Jul 28) Stephen P. Synnott / Voyager 2 (See Despina) Earliest image in the Voyager Image Catalog ( is dated 1989 aug 24.

Proteus (S/1981 N 1; S/1989 N 1) 1981 (May 24) Harold J. Reitsema, William B. Hubbard, Larry A. Lebofsky & David J. Tholen (IAUC 3608); 1989 (< Jun 16) Stephen P. Synnott & Bradford A. Smith / Voyager 2 IAUC 4806 (1989 jul 07) reports "17 frames over 21 d" Earliest image in the Voyager Image Catalog ( is dated 1989 jul 29.

One possibility is that these are "precovery" images. A precovery image is an image that was taken and contains the new object, but nobody noticed it at the time. It happens with asteroids all the time... when one is discovered and an orbit is computed so you know where to look, sometimes precovery images are found from 50 years ago. -- Curps 13:30, 9 Jul 2004 (UTC)

Nope, none of these are precovery. It's just that the original IAUC announcing the discovery did not specify the actual discovery date, nor an MPEC that could be used to ascertain the latter. All that I've been able to do (as seen above) is set a late bound on the discovery dates...
Urhixidur 12:32, 2004 Jul 12 (UTC)
Well the dates we have for Atlas, Prometheus and Pandora are "October 1980", which I think just comes from (in fact, I think that's where all the data on Timeline of natural satellites comes from. But I don't see any more precise information than that.
For satellites discovered from Voyager images, I think there was a different mindset among the scientists than for ground-based discoveries. Normally, when an asteroid or satellite is discovered from ground-based observations, it's important to do followup observations quickly, so the exact date of initial observation is important to record. With Voyager flybies, there was never any possibility of a followup observation by it or other space probes, it was a one-shot deal. Voyager took a lot of images and they spent months slowly analyzing all of them. So, I don't think they attached much importance to the exact date they discovered the images of the satellites...
-- Curps 07:06, 13 Jul 2004 (UTC)

I'd settle for the dates the discovery photographs were taken, but that seems to be well-nigh impossible to get. As a general rule, web access to NASA data is pretty poorly organised, and it gets worse with older stuff, like the 1980s discoveries listed above. Now, if we could just apply the question (in the medieval sense) to a helpless Mr. Synnott...

Urhixidur 04:57, 2004 Jul 14 (UTC)

You could Google his name and try to e-mail him, assuming he isn't retired. But it's not clear that he'd remember. Another alternative might be to try looking up any scientific articles in the online ADS. [1]
It's a bit odd, isn't it? Every single asteroid, no matter how tiny, has an exact date of discovery. But for satellites, it's not the case. -- Curps 09:03, 14 Jul 2004 (UTC)

It gets even more complicated. The date we have for Phoebe is August 16 1898. But if we look at original sources (journal articles, which I've linked to from the Phoebe page), it is clear that the actual discovery was made around March 1899 by William Henry Pickering at Harvard College Observatory, examining photographic plates taken by DeLisle Stewart at Arequipa, Peru in August 1898. In those days, just shipping the plates to the east coast of America probably took months (no Panama Canal yet).

So what's the "discovery date"? The date that the photographic plates were taken, or the date that someone looked at them and realized what was on them? Probably the latter. By the way, Phoebe was the first satellite discovered photographically.

Also, in the case of Triton, we see that Lassell made the first observation of it in October 1846 and suspected that he had seen a satellite. But he observed it only a few times in many months, and it wasn't until 1847 that he put together all his observations and was confident that it was a satellite.

-- Curps 19:36, 14 Jul 2004 (UTC)


In the book "Out of the Darkness: The Planet Pluto", co-authored by Tombaugh and Patrick Moore, we are given the oft-repeated discovery date of February 18, but it is also made clear that the discovery images were taken on January 23 and 29 (see the plates in the middle of the paperback edition). Since we've tended to use date of first photograph so far, we should stick to the January 23 date. We should not hesitate to add the "date the discovery dawned on someone" when it is known, however.

Urhixidur 23:04, 2004 Jul 18 (UTC)

A few problems...
First of all, we should not use the date the photographs were taken — the discovery is only made when a human realizes that something has been discovered. If the photographs are not examined for decades and someone later independently discovers it and then the old images are "precovered", that doesn't retroactively change the date of discovery back to the time the old images were taken.
Second, a book link should not be given as an link, but as ISBN 123456789, which Wikipedia magically converts to a link (you just type in "ISBN" and the number, without [[ and ]]). But in any case, I don't agree that the time of the photos is significant.
-- Curps 00:20, 19 Jul 2004 (UTC)
Didn't know about the ISBN link; good to know. Yes, it would be nice if we could stick to the date that the realisation occurred in the discoverer's mind, but that cannot be done systematically. In following the references, we're often only given the dates the discovery images were taken, not the date they were inspected (e.g. the first outer moons of Jupiter). In other cases the realisation dawned progressively on the discoverer --first a hunch, then an accumulation of confirming observations, then the conclusion. The problem we're going to run into is that whichever definition is used, it'll have gaps...I guess we should strive for the "discovery moment" but still give the discovery image date (and earliest image later found). (It'll still look odd to report S/1986 U 10 as discovered in May 1999...)
Urhixidur 04:27, 2004 Jul 19 (UTC)

This isn't a useful comment, but I just wanted to say.. WOW! My baby's all grown up. ::sheds a tear:: Seriously, though, thanks to everyone who's helped out with this page, I guess the jump start I gave it was worth it. You guys rock. Keep it up. This is now, as far as I know, the best, more conclusive, and clearest collection of satellite discovery info anywhere. :) --Patteroast 02:45, 22 Jul 2004 (UTC)

I just hope it's the most accurate collection too. For many satellites, the exact date of discovery is shrouded in mystery. We got exact info for Phobos and Deimos, but for Phoebe I was unpleasantly surprised when digging into the original journal articles that the date usually quoted for its discovery is simply the date the first photographic plate that it appears on was taken. Those plates were taken in Peru and shipped to Boston on the east coast of the United States... and no Panama Canal in those days... the plates didn't arrive and get examined until many months later. I'm pretty sure that the actual discovery was in March 1899, and it wasn't "August 16 1898".
It's all a little bit discouraging. It seems for many of them we'll never get an exact date. Especially for the ones found on Voyager photos. :-(
-- Curps 04:15, 22 Jul 2004 (UTC)

S/2004 S3 and S4[edit]

Just read all about it, on NASA's site.. seems there may be a new moon jsut outside the F ring.. but it might just be a short-lived clump. Or it could be solid, and have crossed the ring, which would explain both sightings. Either way.. what do we put on the list? :) --Patteroast 21:10, 9 Sep 2004 (UTC)

Complicated Discoveries[edit]

When I overhauled the page way back when, I added the marking some moons with a * to indicate their discoveries were complicated, so people wouldn't be confused to possibly see a moon listed twice, or that the information might be moved innapropriately. Since we now have a much more complete system (showing the date of publication, etc.) I'm not sure if this still fits in. Just thought I'd bring it up, because according to how I'd been doing it, the 12 new moons of Saturn would all get an asterisk (for being announced in a different year than they were discovered). --Patteroast 22:54, 4 May 2005 (UTC)

Put the dates into separate columns[edit]

The situation is currently that the discovery and publication dates are crammed into one column, which makes for a deal of confusion. Also there are many places where the publication date is repeated whereas the discovery date varies, so there is scope for collapsing the duplicate values. If no-one objects I'll have a hack at it when I get my round tuit back. --Phil | Talk 15:54, Jun 16, 2005 (UTC)


Quaoar (4 June 2002), more massive than all asteroids taken together, might deserve an entry. dab () 06:21, 28 July 2005 (UTC)

The first four asteroids were considered planets at the time of their discoveries. If we include Quaoar, we'll end up having to include a bunch of KBO's. --Patteroast 07:51, 28 July 2005 (UTC)
yes I figured that was the reason for not including it. Pluto itself is a borderline case, I suppose? How about using the Mesoplanet definition, which includes Pluto, Quaoar, and four others? dab () 10:11, 28 July 2005 (UTC)
Well, I'd at least expect to see the KBO that's making headlines now in this list. The mesoplanet definition sounds like it might be useful. - 11:36, 30 July 2005 (UTC)
The problem with mesoplanet is that no one uses it. It is a neologism.--Jyril 14:41, July 30, 2005 (UTC)
How about just listing all natural objects in the solar system that are more massive than 1 Ceres... oh... -- ALoan (Talk) 19:48, 30 July 2005 (UTC)
I'm not against adding important asteroid discoveries. But if they're added, the title of this article has to be changed.--Jyril 20:03, July 30, 2005 (UTC)

The title is a bit unwieldy anyway. I do not propose Timeline of discovery of Solar System objects more massive than Ceres1. The title doesn't have to be an exact summary of the contents. How about just Timeline of the discovery of the Solar System, or Timeline of discovery of Solar System objects, and the intro can still state that we're confining ourselves to objects of a certain mass so as not to clutter the article. dab () 07:43, 31 July 2005 (UTC)

Timeline of discovery of Solar System objects sounds perfect. As you say, the scope can be clarified in the lead section (clearly we are not going to list all asteroids, for example!). ALoan (Talk) 11:06, 31 July 2005 (UTC)
Agreed. The asteroid discoveries that should be included (in my opinion): The first four, 433 Eros (first NEA), 588 Achilles (first trojan asteroid), 2060 Chiron (first Centaur), 243 Ida (first binary asteroid), (15760) 1992 QB1 (first KBO), (15874) 1996 TL66 (first SDO), (maybe 5261 Eureka (first Mars trojan) and 2001 QR322 (first Neptunian trojan)), 90377 Sedna and 2003 UB313. Others are just duplicates of the first discoveries.--Jyril 11:26, July 31, 2005 (UTC)
I'm not so sure if this is the right thing to do, but I guess I just liked this list back in the days when it was just moons, since that's my primary interest. I'd support changing this page over to Timeline of discovery of Solar System objects as it seems impossible to go back to those simpler days.. but I just want to reiterate that we're treading a slippery slope. Start with a few asteroids that are included because they are regarded as 'significant', and you'll start running up against people who think different ones are significant, or some listed aren't. Not that I have the solution or anything.. I'll just settle for being a prophet of doom. :P --Patteroast 16:47, 2 August 2005 (UTC)
You rightly point out that some notion of 'significance' is needed. Clearly the discovery of massive trans-Neptunian objects is more significant than the umpteenth rock found in Jupiter's orbit. Also, the explicit listing of the seven classical planets seems a bit, well, redundant (so Earth was discovered in prehistory? pray tell!) Anyway, the slippery slope is there of course. Nobody wants an exhaustive list of Asteroids here (I think). "moons and mesoplanets" sounds like a good guideline to me. dab () 17:00, 2 August 2005 (UTC)
Well, the other approach would be to break the page out into Timeline of discovery of Solar System planets, Timeline of discovery of Solar System natural satellites of planets, Timeline of discovery of Solar System asteroids, etc, but I think it is more useful to have them in one place. Defining our criteria quite tightly should help. -- ALoan (Talk) 17:00, 2 August 2005 (UTC)

2003 UB313[edit]

Should 2003 UB313 included since Nasa called it a "planet"?

Does NASA decide whether something is or is not a planet? What does the IAU call it?
But anyway, see the discussion above: I think consensus if coalescing that so-called "mesoplanets" (and possibly the first of each class of asteroid) should be added and the article retitled. -- ALoan (Talk) 10:40, 2 August 2005 (UTC)
I think we have more or less a consensus that this should be done. Now we just need somebody to go ahead and actually do it :) dab () 10:56, 2 August 2005 (UTC)

Pluto's moons and other news[edit]

First real news in a while! Two new moons of Pluto have been discovered, S/2005 P1 and P2. The date and discoverers aren't clear to me at the moment, but some rough diameters are mentioned in this article: [2]

Also, while looking for information about these moons, I ran into something unusual on the USGS Astrogeology site.. there are listings for 'Margaret (UXXIII, 2003 U3)' and 'Psamathe (NX, 2003 N1)'. What's even more unusual about this is that the previous named and numbered moons of Uranus and Neptune were UXXI and NVIII, which seems to indicate that there are other recently named moons. Anyone got any deeper info on this? --Patteroast 21:41, 31 October 2005 (UTC)

Spurious satellites[edit]

Should satellites that have been shown to be spurios be included in this list? If not, then why Themis is listed?--Jyril 21:39, 3 November 2005 (UTC)

I can't say I like the spurious ones. They really don't belong on this list. Also, I thought the color codes were perfectly understandable, since you never saw moons with that color before the planet was discovered and put in that color... do we really need to be told again at the beginning? --Patteroast 00:32, 26 March 2006 (UTC)
I say banish the spurious satellites to their own article. They're interesting in their own right, but withi this table they risk being simply misleading. The Singing Badger 00:41, 26 March 2006 (UTC)
I'm not at all happy about the spurious satellites, but I notice that the list has contained "Themis" for a very long time. I like having the color code at the top because I always found it confusing without some sort of introduction. Especially when there's a long gap between the introduction of a planet and the introduction of its satellites. Objectively, of course, there's no reason for the colors at all -- since every satellite is labelled with its primary anyway -- but if the list is going to use this system, it might as well be explained. RandomCritic 00:31, 27 March 2006 (UTC)


Why are comets not included in the article?

This is not an article about comets. It was originally intended to be a list only of the planet's moons, but at some point the planets were added to it. The first five asteroids are included because at the time, they were considered planets. --Patteroast 04:54, 5 November 2005 (UTC)


Why are there asteroids in this table? And on what criteria have they been selected? I think (a) the article should be retitled or (b) the asteroids should be removed. Thoughts? The Singing Badger 12:37, 27 March 2006 (UTC)

My understanding is that they were added because at the time of their discoveries, they were considered planets, and all the planets were added for comparison, so.. yeah. I was fine with the first five, but somehow it expanded to fifteen... I like the idea of having the first few there for comparison, just as Uranus, Neptune, and Pluto are in for comparison. But the focus of this article should remain on the moons. I still think we should return to the old title, 'Timeline of natural satellites'. --Patteroast 14:29, 27 March 2006 (UTC)
I see four ways of dealing with the asteroids, all of which seem perfectly reasonable to me:
  • Leave them as they are
  • Delete asteroids 5-15, leaving 1 Ceres, 2 Pallas, 3 Juno and 4 Vesta
  • Delete asteroids 2-15, leaving 1 Ceres
  • Delete all asteroids.

The reason for the "fifteen" is that there was no separate classification of major vs. minor planets until the 16th asteroid was discovered, by which time it was recognized that the list of planets had become overburdened with asteroids. For a while this list had asteroids 1-5 on it, which doesn't make a lot of sense, categorically or historically. RandomCritic 16:09, 27 March 2006 (UTC)

OK, I'm cool with that (I should have read the explanation at the top of the article). But by the way, according to these standards, 2003 UB313 doesn't belong in the table yet because it hasn't been officially declared a planet. So it should be removed until the IAU has made its ruling on the definition of a planet. Right? The Singing Badger 17:07, 27 March 2006 (UTC)
Yeah, but if they do call it a planet it'll just have to go back in again, so I suggest waiting until September to see what happens. If they do decide it's a non-planet, then Pluto might have to go too, and we will probably have a bit of a discussion about the status of "mesoplanets". See the discussion of 2003 UB313 a few sections up. RandomCritic 02:00, 28 March 2006 (UTC)
FWIW, I was looking this up to check the order of Greek vs. Roman names, and was quite surprised not to find any asteroids on it - they were certainly considered planets at the time. Including one to four would make a lot of conceptual sense, from a historical point of view. Shimgray | talk | 14:42, 17 July 2006 (UTC)

Mercury moon[edit]

I'm tempted to revert an edit by CFLeon regarding the name of Mercury's spurious moon. No source was given, and I could find none at Google or NASA. CFLeon wrote that the informal name is "Charley", which I suspect may be this user's first name, though I don't have any particular reason to distrust this user. --Spiffy sperry 21:13, 13 May 2006 (UTC)

Actually, it's based on contemporary newspaper reports with the fellow who actually made the 'discovery'. In an interview, he said that, if it was confirmed, he'd like to name it 'Charley' because he once had a dog named that and he always wanted to name something after the dog. I suspect he was joking, but it was published and became the only name given to the object. I can't find a reference online, but check AP newspaper filings in the time period (March 1974). Sometimes I can't finish things in one post. (And I have NEVER been called "Charley", since another relative was already.;)) CFLeon 21:34, 13 May 2006 (UTC)
Doesn't sound like it's a name that was actually in use (or would ever have been used). I agree with removing the edit. RandomCritic 15:44, 15 May 2006 (UTC)

Asteroid moons[edit]

I'm really not comfortable with listing asteroid moons like Dactyl in this list. Perhaps another list or another page could be developed for them; the list really ought to be limited to the planetary moons it was intended for. Ida has never been considered a planet.

An asteroid moon list, though it would be short now, has the potential to become quite extensive; depending upon the decisions of the IAU this September, the moons of Pluto and 2003 UB313 might even end up on that list. RandomCritic 17:27, 15 June 2006 (UTC)

Hi Random, I hear what you're saying, and I would also be totally against adding random asteroid moons in. Same as for adding random asteroids or TNOs. My rationale for putting in Dactyl (and only Dactyl) is that this is the first of a qualitatively different class of bodies, so it is useful as a reference. I figure that since the first 15 asteroids are in there despite the article title, and the moons of UB313, then by the same logic the first asteroid moon is also fitting. No more, though. Deuar 17:42, 15 June 2006 (UTC)

I'd rather dump the asteroids. They already have their own lists. But I guess that's a different question. If we follow the "first of class" rule then we would get rid of everything except Ceres. If I understand the history of this page correctly, it started out as a list just the satellites; then for the sake of comparison the primaries of those satellites, at least those discovered since 1610 were added; and then "prehistory" was added as a sort of baseline, which brought in the rest of the planets; then the asteroids which had been considered planets at one time. Comets aren't in, because comets were never considered planets (though some planets have been considered comets!). With the addition of Dactyl, however, I'm no longer very clear on what sort of a list this is.

To some extent, it serves as a documentary record of the discovery of the Solar System, but obviously it can't be complete, because there are hundreds of thousands of known asteroids (not to mention comets), a burgeoning number of KBOs, etc. So are we focusing on "milestones"? If so, do we have a way to determine what is a milestone and what isn't? Are we still committed to listing every last circumplanetary rock, ring particles excepted, that gets discovered? Maybe it's time for thought on where this is eventually going, short and long term. What do we want this page to look like in 2010? 2050? 2100?RandomCritic 21:33, 15 June 2006 (UTC)

If need be, the page could split into more specific articles if it becomes ungainly. As it is, I could deal with removing some of the asteroids and don't think there should be any asteroid moons, even as an example... but I don't think anything that's classified as the natural satellite of a planet should be removed from this list, even if it is just a mile-wide rock. If we get to the point where they vastly outnumber larger bodies, the page could be split by time period. Or maybe there will eventually be a lower limit for what classifies as an official moon at some point... who knows? Anyway, other than the random things creeping into the list over time, I'm quite happy with the current state of it. --Patteroast 03:14, 16 June 2006 (UTC)
Going by just the title of the page, all asteroids should be out, UB313 also for now, Pluto we will see if the IAU ever makes its mind up, as well as removing the prehistory section since these objects were never really "discovered" in the usual sense of the word. Of course the prehistory section is kind of nice and may be good to keep. The irregular satellite plankton around the giant planets has a tendency to swamp everything else after 2000, but I think it's useful including it if only for giving a sense of perspective about moon discoveries. Finally what about the "Spurious satellites" section? If we were being consistent shouldn't all purported satellites be recorded here? Like (I shudder) various named objects seen during rign-plane crossings or flybys that were never recovered or turned out to be ring clumps? What about spurious planets like Vucan or good old Planet X? Deuar 13:33, 17 June 2006 (UTC)
As this sort of editing has to start somewhere, I've begun by removing the asteroids and the spurious satellites list, since there seems to be some agreement that they don't belong on the page. I'm copying the removed text below, so they can be replaced in whole or part if this seems too drastic. RandomCritic 07:19, 19 June 2006 (UTC)
Follow-up: I've removed the 2003 UB313 material and Dactyl as well and copied the material below. I note that this material is already covered in the articles Asteroid moon and List of asteroid moons. RandomCritic 08:12, 19 June 2006 (UTC)
Looks like a good move to me. Deuar 14:34, 19 June 2006 (UTC)

Deleted sections[edit]


For comparison, discovery dates of the first fifteen asteroids are also included, down to the end of 1851. Beginning in 1852, in light of the fact that new asteroids were being discovered every year (eight were discovered in 1852 alone) and that it was becoming difficult to find appropriate symbols for all of them, the asteroids were placed in a new section in astronomical almanacs and given a new notation to replace the old symbols. For several decades, however, at least Ceres, Pallas, Juno and Vesta were considered full-fledged planets.

Date Name Designation Image Planet/Number Designation References/Notes
o: March 28, 1802 2 Pallas 9th Planet (1802)
Asteroid (1851)
o: September 1, 1804 3 Juno 10th Planet (1804)
Asteroid (1851)
o: March 29, 1807 4 Vesta Vesta-HST.jpg 11th Planet (1807)
Asteroid (1851)
o: December 8, 1845 5 Astraea 12th Planet (1845)
Asteroid (1851)
Hencke [3]
o: July 1, 1847 6 Hebe 14th Planet (1847)
Asteroid (1851)
Hencke [4]
August 13, 1847 7 Iris Asteroid Hind
October 18, 1847 8 Flora Asteroid Hind
April 25, 1848 9 Metis Asteroid Graham
April 12, 1849 10 Hygiea Asteroid de Gasparis
May 11, 1850 11 Parthenope Asteroid de Gasparis
September 13, 1850 12 Victoria Asteroid Hind
November 2, 1850 13 Egeria Asteroid de Gasparis
May 19, 1851 14 Irene Asteroid Hind
July 29, 1851 15 Eunomia Asteroid de Gasparis
August 28, 1993 Dactyl S/1993 (243) 1 243 Ida I Galileo [5]
Spurious Satellites[edit]
Date Name Designation Image Planet/Number Designation References/Notes
1672 "Neith" Venus (spurious) Cassini [6]
April, 1861 "Chiron" "Saturn IX" (spurious) Goldschmidt [7]
April 28, 1905 /
April 17, 1904
Themis orbit.gif
"Saturn X" (spurious) Pickering [8] [9]
March 27 1974 "Charley"(informally) S/1974 H 1   Mercury (spurious) ? [10]


I notice that Perdita is listed twice, the second time with the annotation "Recovered by the Hubble Space Telescope", but no other body seems to get this special treatment, while I'm sure many others were also recovered only after an appreciable period. I suggest removing the second mention altogether. Deuar 14:31, 19 June 2006 (UTC)

Isn't the treatment of Perdita like that of Janus, Epimetheus, Themisto, and Methone? I note on review that the list is inconsistent in its use of asterisks (apparently referring to the "complicated discoveries" note at top). RandomCritic 15:03, 19 June 2006 (UTC)
Ok, after reading Perdita (moon) it makes sense. I thought it was a much more mundane case because the time period between discovery and rediscovery was small, and both are credited to the same person. Deuar 15:39, 19 June 2006 (UTC)
As I noted in the complicated discoveries note I left on this talk page, they seem to have wandered away from their original purpose. Originally, I put that note on any moon that was announced or confirmed in a year other than the one it was discovered... but I'd support only noting the special circumstances of moons like Janus, Epimetheus, Themisto, Methone, and Perdita, where at least a couple years goes by. --Patteroast 16:45, 25 June 2006 (UTC)

Timeline of natural satellites[edit]

Why was the redirect linked above changed into an independent page? What is the point? RandomCritic 02:17, 24 June 2006 (UTC)

On closer inspection, I suspect this is a tacit POV fork. TONS is identical to TODOSSPATNS except that all the planets have been taken out. If that was an issue, I think it would have been better discussed here. As it is, the new article seems redundant to me; it contains no information not in this list, and the ratio of planets to satellites in TODOSSPATNS is so low as not to make the satellite information difficult to access. RandomCritic 02:25, 24 June 2006 (UTC)
Yes, this is bizzare. It appears to have been a redirect, then was made into a duplicate of the main article Timeline of discovery of Solar System planets and their natural satellites by User:Acom on 23 June 2006. Plus it has an uninformative name. I reckon that duplicate page should just be deleted. No need even for a redirect there. Deuar 15:35, 25 June 2006 (UTC)
That page was the original name the timeline went by, so I'd still suggest a redirect at its location. Still like the old title better, myself. :P But I agree, there's no reason to have two pages for this. --Patteroast 16:41, 25 June 2006 (UTC)
The page has been reverted to a redirect. RandomCritic 03:10, 26 June 2006 (UTC)

New Moons of Saturn[edit]

Two MPECs relevant to this page:

RandomCritic 13:17, 27 June 2006 (UTC)

Since nobody seemed keen on making them some stubs, I went ahead and did it myself. Now someone just needs to go fact-check my stubs to make sure they're accurate. :) -Patteroast 16:27, 16 July 2006 (UTC)


Shall we include the proposed new (and in one case, old) planets in this list? 1 Ceres and 2003UB313? RandomCritic 11:29, 16 August 2006 (UTC)

Two old cases - don't forget Charon. Shimgray | talk | 11:31, 16 August 2006 (UTC)
It's too early. Wait until the proposal has been accepted and formally instituted. The Singing Badger 11:51, 16 August 2006 (UTC)
No problem. Charon's already on the list as a moon; it would just have to be altered (or annotated) to reflect its new status. But if there is one part of the proposal that I'd expect the IAU to reject, it might be the definition of satellite vs. planet.
One less controversial alteration I'd like to make is to remove the "Sol I" - "Sol IX" designations, which I think are unofficial, and just substitute "planet". The enumeration is probably doomed no matter what decision the IAU takes. RandomCritic 12:18, 16 August 2006 (UTC)
Done. RandomCritic 15:29, 17 August 2006 (UTC)

Bad dates?[edit]

In the course of annotating the dates provided in the left-hand column, I found that I could not verify the dates given for the rediscovery of Janus (January 19, 1980) and Epimetheus (January 26, 1980). These dates appear to be at variance with the information in the references. I think that perhaps they should be February 19, 1980 and February 26, 1980, but I would very much appreciate it if someone would doublecheck these facts for me before I make any changes.

I am also having trouble discerning the relevance of notes 56, 57, and 58 to the discovery of Adrastea -- they all mention 1979 J1 tangentially, but do not as far as I can tell provide useful information about its (earlier) discovery. I was wondering if they had been misplaced. Some explanation would be helpful. RandomCritic 16:59, 21 August 2006 (UTC)

Notes on the Prehistory section[edit]

This section has probably gone through more purely aesthetic changes than any other part of the page. Since it seemed to have finally settled down to a shape that everyone could live with, I think it's probably wiser not to drastically change it.

There was some question about whether the section was actually needed; there is no record of any of the eight objects involved being "discovered", and some of them certainly never were discovered in any sense. The Prehistory section does, however, have the important function of establishing the structure of the Copernican Solar system as it was understood on the eve of Galileo's discovery of the Galilean satellites.

It is not a chronological summary of the probable order of the discovery of the various planets, which would necessarily be conjectural. The Sun and Moon have certainly been known to exist by humans since before they came to be humans. Of the planets that appear starlike from Earth, we can guess that Venus was the first to be recognized as something different from the other stars, and Mercury and Saturn were among the last. But none of this can be established with any certainty.

The only one of the "Prehistoric" planets whose discovery, in a sense, we can point to with any accuracy is the Earth -- which, while always known to exist, was not recognized as a planet until the publication of Copernicus' 1543 opus. But it's not listed here because a theoretical change, no matter how revolutionary, does not satisfy our criteria for discovery of a planet or satellite.

The organization of the Prehistoric section cannot pretend to be chronological. The alternative is a thematic grouping. Currently, the organization can be justified this way:

It starts with the Sun, as the center of the Copernican system. It is then followed by the planets, in order from the Sun outward. The Moon in the Copernican system is no longer a planet, so it is listed apart from them; as also the first of the natural satellites to be known (and, in the Copernican system, the first to be recognized as a satellite distinct from a planet), it is suitably the last object mentioned before the historical list begins, leading off the list of the natural satellites. If anyone has a better idea about how this section should be arranged, please discuss it here before making changes. RandomCritic 15:30, 22 August 2006 (UTC)

New rulings[edit]

We now have eight planets and an unspecified number of "dwarf planets". Would it make sense to expand this timeline to cover "planetary bodies" rather than just "planets"? To clarify - that means "add Ceres and 2003UB313", and possibly a few more in the long run. It doesn't mean we're going to clutter the article overly. Shimgray | talk | 14:38, 24 August 2006 (UTC)

I think it would be wrong to exclude Pluto on the basis of an administrative classification, when the discovery of its satellite Charon was one of the more significant discoveries of the later 20th century -- not least because it allowed a better ascertainment of Pluto's mass.
Let me suggest the following as a rule -- the list, intended to be a list of satellites, and only secondarily of planets, should include any "dwarf planet" only when such an object is shown to have a satellite. Objects without satellites are not included (and at present the only examples of such are in our already anomalous Prehistory section). That would mean that we include Pluto and its three satellites; 2003 UB313 and its satellite; probably 2003 EL61 and its satellites; but not Ceres or the others. Smaller asteroids with moons would not be included. RandomCritic 16:09, 24 August 2006 (UTC)
Added back 2003 UB313 (as "dwarf planet") and its satellite as probably the least controversial of these additions.RandomCritic 02:10, 25 August 2006 (UTC)
I think we should just put in all the accepted dwarf planets and their satellites. There aren't so many that it will be a problem, and the discovery of Ceres was, after all, a fairly major event for our understanding of the solar system. Anyway, there are so many irregular satellites of the outer planets here already that adding a couple of bodies more or less won't make a difference to the clutter. Deuar 10:13, 25 August 2006 (UTC)
Well, at this point that's just 1 Ceres, so, okay, fine, back in it goes. RandomCritic 16:53, 25 August 2006 (UTC)

imaging date[edit]

I really like the fact that we're now labeling the different dates with i:, o:, p:, but now that this has been made more explicit a new ambiguity appears that should be sorted out and explained explicitly in the introduction: When giving the "i:" imaging date, how should precoveries be treated? The two most obvious choices to use are

  1. The earliest precovery image by anyone
  2. The earliest image by the discoverers

I'm not sure which is preferable and/or more commonly used. Any ideas? Deuar 09:46, 30 August 2006 (UTC)

For future reference[edit]

The discovery of Larissa (moon) seems to be a little more complicated than the table notes; it had been earlier observed as 1981 N1 and then lost.

I don't think the imaging dates are right for S/2002 N1, N2 and N3. RandomCritic 06:36, 31 August 2006 (UTC)


Should we also add Ceres to the table?--Nixer 11:31, 11 September 2006 (UTC)

Seems to be there. Deuar 15:18, 11 September 2006 (UTC)

Larissa and other complicated discoveries[edit]

For example Larissa, which was first given a provisional designation in 1981, then another in 1989. It was appeared on the list in 1989, but now I have moved it to 1981. However, I'm wondering whether we have any particular ordering policy in such cases. According to earliest provisional date? Latest provisional date? Gut feeling? Deuar 18:29, 13 September 2006 (UTC)

When first putting in notice of the complicated discoveries, I considered moons in which independent discoveries or confirmations were made more than once and years apart. There's not a very rigorous system... but I'd say that if Larissa wasn't immediately recognized as the 1981 object in 1989, and the independent observations clarified the situation as to the existence of the moon, there should be a mention both in 1981 and 1989. But of the options you gave, I think this is closest to gut feeling... --Patteroast 18:34, 13 September 2006 (UTC)
Actually, scratch the not being immediately recognized part. Even if the observation session was specifically planned to pick up the object seen before, a gap of years between first sighting and recovery is still worth two mentions. --Patteroast 18:37, 13 September 2006 (UTC)
Sounds reasonable. So maybe a rough heuristic would be
  • The discovery date used to determine order on the list is the first one that was recognised as likely belonging to a satellite (i.e. likely enough to be given a provisional designation). This avoids delving into precoveries.
  • If a gap of years of uncertainty existed between the first discovery and later recovery then tag is as complicated with a star, and give both dates.

? Deuar 19:10, 13 September 2006 (UTC)

That sounds about right to me. --Patteroast 17:33, 16 September 2006 (UTC)

Asteroids again[edit]

I see that a user added asteroids 2-6 to the table again, but I believe we had a consensus that they should not be there, so I am going to take them out again. RandomCritic 17:03, 16 September 2006 (UTC)

Newly named Neptunians[edit]

I was browsing, and I notice we finally have a Neptune IX, as well as XI, XII, and XIII! Unfortunately, I am somewhat mystified by the dense formatting, and was only able to insert the names. (Halideme, Sao, Neso, and Laomedeia) Can someone with better table skills add in the following?

Neptune IX = Halimede
Neptune XI = Sao
Neptune XII = Laomedeia
Neptune XIII = Neso

Thanks! --Patteroast 22:58, 30 January 2007 (UTC)

et al.[edit]

hi, what does this mean? et al. //User:Frizabela

Abbreviation of Latin for 'and others'. It's commonly used when there are several people to credit a paper to. The discoveries with et al. were announced in such a way. --Patteroast 18:50, 23 July 2007 (UTC)

Some who can edit the table...[edit]

I've finally given up on ever figuring out how to edit that table without horribly breaking everything. Could someone please add the following info for newly named moons:

S/2006 S 6 = Saturn L Jarnsaxa
S/2006 S 4 = Saturn LI Greip
S/2007 S 1 = Saturn LII Tarqeq

Articles in question have already been moved. --Patteroast 17:09, 21 September 2007 (UTC)

I've added Jarnsaxa, but had problems with Greip and Tarqeq. Anyone else? --Ckatzchatspy 19:25, 21 September 2007 (UTC)

Fair use rationale for Image:Xenaandgabrielle.jpg[edit]

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BetacommandBot (talk) 08:01, 15 January 2008 (UTC)


There's a new dwarf planet! Shouldn't this be included in the list now? Werothegreat (talk) 00:04, 17 July 2008 (UTC)

Sedna missing[edit]

Since Sedna is of principal interest: it is believed by at least some researchers to be an inner Oort cloud object and it it the first very massive such. Said: Rursus () 09:28, 30 December 2008 (UTC)

I inserted Sedna. I tried to make it as similar to Makemake as possible, choosing a similar but not same color, but I might have missed the color logic, if such is present. I didn't choose to link to Dwarf planet candidates, since that is of less interest, instead I linked to detached object, the category to which Sedna is the most prominent object. Said: Rursus () 10:19, 30 December 2008 (UTC)
I also updated the legend accordingly, although that provides potential chaos to the previously nice legend structure. Instead there maybe should be a legend subsection "other principal SSSB:s", of which Sedna is one. Said: Rursus () 10:46, 30 December 2008 (UTC)

Asterisk after several names[edit]

What mean an asterisk after the several names, e.g. Epimetheus? Please note this in the article. — Chesnok (talk) 10:19, 2 January 2009 (UTC)

Asterisk is explained in the note at the beginning of the article. Ruslik (talk) 10:51, 2 January 2009 (UTC)

Pallas, Juno, and Vesta[edit]

were considered planets for several decades so they should be listed here. Nergaal (talk) 00:15, 21 December 2009 (UTC)


Today's the four hundredth anniversary of Galileo's discovery of the Galilean satellites. RandomCritic (talk) 11:53, 7 January 2010 (UTC)

WP:FLC delisting risk[edit]

This list has been identified at WP:FLC as being "at risk" of delisting. This basically means that it's still in a reasonably good shape, but that it needs updating in line with current featured list standards. If the list is not improved, then it will be nominated at WP:FLRC.

For details, see User_talk:RandomCritic#Timeline_of_discovery_of_Solar_System_planets_and_their_moons.

I have disabled the above link as I do not approve of my personal talk page being used for this discussion, which in no way relates to my editing activity. The correct link is Wikipedia:FLRC#Timeline of discovery of Solar System planets and their moons. Please go there to comment if you care about this issue.RandomCritic (talk) 23:06, 27 November 2010 (UTC)
  1. We no longer start with "This is a list..." or "This timeline..." - we now expect an article-standard introduction, so, in this case two or three paras of good prose to explain what were about to read, which adequately summarises the list.
  2. References to online sources could use accessdate parameters.
  3. WP:ACCESS says we shouldn't just use colour to express a particular property, we need a symbol (or something which isn't colour-dependent) as well.
  4. Inline links such as "Systema Saturnium ", " Kosmotheôros" etc should be avoided.
  5. Bold is discouraged to indicate a particular property, per WP:MOSBOLD.
  6. While the table footers aren't explicitly discouraged, they are highly unusual, and not really needed.
  7. References/Notes -> what does "Herschel" mean to a non-expert? Perhaps "Discovered by Herschel" would be more obvious.
  8. Consistency on linking is required. You don't relink Kuiper, for instance, but you do relink Kowal.
  9. Blank cells are not great, for those without images, I'd suggest an en- or em-dash. Same for those blank cells for nameless moons.
  10. What makes the first of the External links reliable?
  11. The link is dead.
  12. As is the link.
  13. Some refs are actually notes, e.g. [4] and [5]... and they need to be referenced.
  14. What is IAUC? Is it linked/expanded anywhere?
  15. Checklinks (here) says four links are dead.
This is a quick sample of some of the things that stood out. The Rambling Man (talk) 16:38, 14 November 2010 (UTC)

WP:FLC delisting continued[edit]

Although still an active issue, the discussion is now found at Wikipedia:Featured list removal candidates/Timeline of discovery of Solar System planets and their moons/archive1. Urhixidur (talk) 21:27, 4 January 2011 (UTC)

Asteroids and spurious ("lost") moons[edit]

Since 2006 it has been clear that asteroids (other than "dwarf planets") and their moons, and "lost" or spurious moons would not be included on this list, as discussed already in the relevant Talk: sections above. If there is a case to be made for reinstating them, it should be discussed here. My own feeling is that a moon should actually exist in order to be listed; there have been any number of false discoveries of imagined or non-existent or irrecoverable moons, whose inclusion would diminish the list's utility. And asteroid satellites, of which there are a very large number, are already discussed in the article Minor planet moon; if it's desirable to chronicle their discovery dates, then it should be in a separate table, either in that article or in a new one linked to it, which includes all of them.

This article is primarily about planetary moons. The discoveries of Uranus, Neptune, Pluto, Eris, and Haumea are included because they are relatively sizable objects (planets or "dwarf planets") with satellite systems, and the discovery of the planet is, of course, a prerequisite for discovering their satellites. But Vesta, Hygiea, etc. are not known to have satellites and are considered too small to be "dwarf planets". There is little utility in including them in this list; the discovery dates of asteroids are chronicled elsewhere, and the total number of asteroids is far too vast to be included in this list, whether they were ever considered planets or not.RandomCritic (talk) 19:04, 28 July 2011 (UTC)

the Prehistory section[edit]

There is some confusion in the prehistory section. Obviously people have been looking up at the planets and noticing them forever, but it wasn't until historical times that anyone knew they were planets. I would say that if we were going to make this a historical list we would need to place the Sun and Moon in prehistory; the planets in antiquity (with Venus first, as it was the earliest planet whose motions have been recorded), and Earth in 17th century, which is when it was recognised as a planet. Serendipodous 17:49, 22 August 2011 (UTC)

See comment above.RandomCritic (talk) 14:29, 31 August 2011 (UTC)

File:2003 EL61.jpg Nominated for speedy Deletion[edit]

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10th, 11th and 12th planet missing[edit]

It is quite confusing to not find those in the list. Neptune is listed as being 13th Planet (1846). Either take that away, or put the three missing "planets" there as well. Per above discussion, they seem to have been Pallas, Juno and Vesta. And actually, while 9th planet is there; it is Pluto, which was found only in 1930, so the 9th is also missing... (talk) 16:45, 3 December 2014 (UTC)

The 9th was 2 Pallas (1802), the 10th was 3 Juno (1804), the 11th was 4 Vesta (1807), and the 12th was 5 Astraea (1845). Nothing is missing. I'd be hesitant to put these in, because that would force all the asteroids up to 15 Eunomia in (after that they got demoted from planethood), but an explanatory note would certainly help.
The Galilean moons and five of the large Saturnian moons (Tethys, Dione, Rhea, Titan, and Iapetus) were also once considered to be planets, but I don't know if they were ever numbered in sequence. Such a numbering would certainly be very awkward, because they orbit around other planets (Jupiter and Saturn). Double sharp (talk) 10:58, 9 December 2014 (UTC)

Asteroid planets[edit]

The 1800s asteroids that were at the time considered planets, should all be listed here, not just only Ceres. They are documented to have been called "planets" at that time. If we're listing all the moons of the giant planets, I don't see why we wouldn't list these also. We might also list the discovery dates for the ring systems of the giants as well. -- (talk) 09:14, 6 March 2017 (UTC)

According to [11] The U.S. Naval Observatory, the first four asteroids were generally considered planets, while 5-onwards were less so, since there was a 40 year gap between #4 and #5's discoveries. This would be similar to the controversy first started by 1992 QB1, and then Eris, and the gap with Pluto. -- (talk) 05:49, 9 March 2017 (UTC)

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text formatting in the tables[edit]

I love, love, love the tables in this article!! One question... in the "name" columns... what is the significance of roman vs. italic vs. bold type? I've been scanning the article for clues. Please pardon me if I've missed it.... PurpleChez (talk) 14:06, 11 January 2018 (UTC)

From the first sentence of "Key": "In the following tables, planetary satellites are indicated in bold type (e.g. Moon) while planets and dwarf planets, which directly circle the Sun, are in italic type (e.g. Earth)." (The Sun is, of course, in roman type.) Double sharp (talk) 15:15, 11 January 2018 (UTC)


There's so much valuable information inside these tables, I wonder if there's any way to add metadata to them, to allow the data to be used for visualisations, analysis, etc. Flycatchr 19:17, 23 April 2018 (UTC)

Requesting a little change.[edit] all objects that were once called planets to be added.

note that this list does include all that except for the first 3-4 or 14-15 asteroids , the first 3 were called planets for a long time and the 5-15 were called planets for 4 years. ive wonder were the first few asteroids would be place in this page , of course we cant put all , but since the first so call 15 where called planets once , i was wondering if we could re add them. Joshoctober16 (talk) 13:22, 3 January 2019 (UTC)