Pluto has another moon!

By Phil Plait | July 20, 2011 8:57 am

This is pretty nifty: astronomers have discovered a fourth moon orbiting Pluto!

The tiny chunk of ice was found in Hubble images taken just a few weeks ago, and was clearly seen among the three previously known satellites:

It doesn’t have a name yet — it’s designated S/2011 P1 (or just P4 informally) — and it’s only about 13 – 34 km (8 to 21 miles) across. The size is estimated by measuring its brightness and assuming it’s icy like Pluto itself — a more reflective (white or icy) object would appear brighter than a darker object if they are the same size. Since its actual reflectivity isn’t known, the size has a wide range. But it’s still pretty dinky. For comparison, Pluto itself is 2300 km across, and its biggest moon Charon is well over 1000 km in size. I’ll note our own Moon is 3470 km across, so even Pluto is pretty small.

The thing is, in that single image above you can’t be sure if the object is a moon or a coincidentally placed background star. The solution: take a second image! That was done, clinching the moon’s identity:

See how it’s moved? Mind you, in the week or so between these two images Pluto moved substantially compared to background stars, and the moon moved along with it around the Sun at the same time it’s going around Pluto. You can see the motion of the other moons as well.

In the image, the diagonal lines are an optical effect inside the telescope itself. Pluto is very bright, so the astronomers used some processing techniques to make it appear much fainter, taking multiple images and subtracting one from the other to remove the glare of Pluto (it doesn’t work perfectly, which is why there is a black strip across the image; that blocks unwanted noisy light). I did this myself on many images when I worked on Hubble. It’s amazing how well it works, as you can see in the image above.

Mind you, Pluto was 5 billion km (3 billion miles) from Earth when this image was taken! But we’ll soon get much better pictures: the New Horizons probe will fly past the tiny world in 2015, snapping away as it does. We’ll probably learn more about Pluto in a few hours than we have since its discovery in 1930.

I wonder what they’ll name this iceball? The two moons Nix and Hydra (discovered in 2005) were named after Roman mythological characters associated with night time and Pluto. Cerberus seems like an obvious choice, but there’s already an asteroid with that name. Maybe they can change the spelling a bit to Kerberus to get around that. There’s already an asteroid named Persephone, too, if you’re curious. We’re running out of good names!

Well, whatever it’ll be called, it’s there, and we’ll see it up close in personal in just a few more years.

Credit: NASA, ESA, and M. Showalter (SETI institute)


Related posts:

- Ten Things You Don’t Know About Pluto
- The Unbearable Roundness of Being (about the definition of "planet")
- Pluto may still be the biggest dwarf planet
- Pluto wanders into a Messier situation

CATEGORIZED UNDER: Astronomy, Cool stuff, Science, Top Post

Comments (120)

  1. Ronan

    Fantastic! Hopefully New Horizons will get some good imagery of the new Pluto system!

  2. J. D. Mack

    Call it “Fagen”, after the man who recorded the album “The Nightfly”

  3. Anon

    When will the IAU realise that Pluto isn’t a dwarf planet, but that Pluto-Charon is a double dwarf planet? Neither orbits the sun directly – they orbit each other, and their barycenter orbits the sun.

    More OT though, I’m very excited about this. I hope New Horizons will be able to snap a lot of nice pictures of the Pluto system, and maybe discover new moons/rings itself.

    I hope they don’t go with Persephone – she was Hades’s wife, and imho Charon should have been named Persephone. Making a 20 km chunk of ice Pluto’s wife would just be weird. I love Kerberus though.

  4. Michelle

    Back when I was a kid, I was going around in a DOS program called Orbits and learning how Pluto just had one big moon (by comparison to the main body). A few years back I learn it has two more… And now it has a fourth!

    I never cared much about the planet status being lost. That doesn’t change a thing about the nature of Pluto, and how it kicks ass. It’s one of my favorite bodies in the solar system. Small and mysterious, so far away. I can’t wait for New Horizons to get over there and show us all that!

  5. Silber

    My suggestion for the moon’s name would be Aquila. I know it’s not been discovered today, but since the discovery was announced on the Anniversary of Eagle landing on our moon it seems fitting. Now quick, someone come up with some connection between Hades/Pluton/Seth/any Underworld-God you can think of and an Eagle, because I can think of none.

  6. Joe

    I humbly suggest “Granata” as a name. Latin for “seed”, and the root word for “pomegranate”.

  7. Glauco

    Pluto is gathering his friends and will claim back the status of a planet by force.

  8. Jeeves

    Little old Pluto seems to have more than its fair share of moons, doesn’t it? I would like to propose a new law of astronomy (call it Jeeves’ law):

    The number of moons around an object orbiting the sun is proportional to the product of (1) the object’s mass and (2) its distance to the sun (give or take a “squared” or two).

    Discuss.

  9. Michael

    @Anon: The earth and our moon also orbit their common barycenter. Does this make the earth and moon a double planet?

  10. allium

    Picking up on Silber’s suggestion, one of the Hecatoncheires (“the hundred-handed ones”, giants in
    Greek myth that were cast into Tartarus once by Uranus, and again by Cronus before being freed by Zeus) was named Gyges, “big-limbed”. That’s probably as close to Armstrong as you’re going to get.

  11. Another Eric

    Even more remarkable is the fact that this is the first time I’ve ever heard that Pluto had more than ONE moon (Charon). When were these other moons discovered, and why wasn’t I informed???

    Ah – The other moons were discovered in 2005!! (I went back and reread what Phil wrote), I must have been too busy working on my house to notice this info – LOL

  12. Stephen

    Is the graininess of the photo simply an effect of photographing such a distant object, or is that noise from the Kuiper belt?

  13. Mike

    So how close does New Horizons have to get to Pluto before it’s capable of taking better pictures than Hubble? What date does that happen?

  14. Sarah

    Cool! And I think in the spirit of 21st-century abbreviation-of-everything (and this is a tiny moon after all) that Sephie, short for Persephone, would be a great name. And contrary to Anon, I think naming a chunk of ice after Hades’ wife has a wonderful irony to it!

  15. Surgoshan

    Michael, the sun and all our planets orbit a common barycenter… does that mean we’re not a solar system at all, but rather an icosadodecatuple plumbet?!

    I suspect anon’s definition relies on the fact that the barycenter of the Pluto/Charon system is outside either object. The Earth/Moon barycenter is inside the Earth, so there’s that. P/C distinctly orbit about that common center, whereas Earth just has a wobble in its orbit.

  16. FoxtrotCharlie

    Really? We need to stop calling chunks of Ice “moons”, I’ll accept satellite. And yes this does mean I don’t really consider those chunky potatoes Mars has “moons”. Because of the nature of the orbits, Charon-Pluto is more of a double “dwarf planet” system than planetary dwarf with moons system.

    You know words like Planets and Moons used to mean something, but now everything is a “moon” and some people would have a solar system made “20 or so planets”. Call me whatever you want but it’s just weird to me to have Titan and Hydra share the same classification: “moon”.

    On the other hand like the term Plutoid much better than “dwarf planet”. We can always revisit these classifications if we find really large plutoids the size of Earth or whatever (I highly doubt it though, such an object would perturb it’s orbit quite a bit even if it wouldn’t clear it, but maybe we just don’t have the instrumentation to find one. In the future we’ll have a better map of the Kuiper belt.

  17. Proserpina, being the Roman name for Persephone, strikes me as most appropriate.

  18. CB

    So cool. Why can’t 2015 be tomorrow?

    Oh, and FoxtrotCharlie, hate to break it to you, but “planet” and “moon” didn’t really mean anything, they were vague and nebulous terms and it didn’t really matter because we didn’t know of enough objects to challenge our half-formed intuition. To the extent a definition even existed, all the objects you’re complaining about counted as moons so I don’t think looking to the past is the answer to your conundrum. :P

    However I do agree that “Plutoid” is a better name, if only for style points.

  19. sohvan

    I agree that Pluto should be reclassified to a double dwarf. It seems like we’ll need another revision of the classification system once we start finding some more exotic exoplanets. It’s not easy to come up with a good system to say what is a moon and what is a planet.

  20. Mike Richards

    Has Alecto been taken for another object? She was supposedly Pluto’s daughter and one of the Furies.

  21. Thespis

    I suggest Minos- tie-breaking judge of the underworld. I don’t *think* anything’s been named after him yet, but please enlighten me if it has!

    ETA:
    (Emily Litella voice: “Nevermind.”)
    http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=6239+Minos

  22. Oh, I see. So now that Pluto is no longer a planet it just has to hog all the moons.

    @7. Jeeves: there’s actually something like that already. It’s been noted that the ratios between the masses of the giant planets and the total mass of their respective moons are all around 10^4. That is, Jupiter, Saturn, Uranus, and Neptune are each roughly 10,000 times more massive than the sum of the masses of their moons. It’s possible there’s some physical reason and that satellite systems can’t get any larger than that.

    Note that obviously our own Moon is way too massive for this rule as well as the Pluto/Charon system. So it’s not perfect.

    @20. Mike Richards: According to my wikisearch: nope

  23. FoxtrotCharlie

    CB, actually the further you go back the further moon had more sense because we only saw the big ones. A long time Ago Saturn had only Titan. Jupiter had it’s big four. And please don’t use that condescending “I hate to break it to you”, I’m well aware of the history of these “nebulous” terms as you put it. Before the definition was a simple discreet set. Of course now that we have so many different objects we have all this weirdness going on.

    It’s kind of hilarious because for a time, Ceres was considered planet until they found all those chunky rocks sharing its orbit. Then they called it an asteroid. If the rest of the KBO had been discovered at the time Pluto, that dinky thing would never have been called a planet.

    The reason we run out of names is that we rush to name every little pebble in the sky without thinking about it. I’m sure they’ll find something for P4. Personally I’d just call it Chivas or Dewars, more appropriate for an icy rock.

  24. MattF

    Surgoshan: I suspect anon’s definition relies on the fact that the barycenter of the Pluto/Charon system is outside either object. The Earth/Moon barycenter is inside the Earth, so there’s that. P/C distinctly orbit about that common center, whereas Earth just has a wobble in its orbit.

    If that’s so, anon, how would you classify a body with a relatively massive secondary that had a highly elliptical orbit, so that the barycenter of the system was well below the primary’s surface at periapsis but above the primary’s surface at apoapsis?

    These things don’t care what we call them.

  25. FoxtrotCharlie

    If that’s so, anon, how would you classify a body with a relatively massive secondary that had a highly elliptical orbit, so that the barycenter of the system was well below the primary’s surface at periapsis but above the primary’s surface at apoapsis?

    Annoying.

    In a more serious note, I would need to do the math, but such a system does not sound stable to me. If the secondary is massive enough it may well eventually settle in a such a way as to make it a true double. If not, it will be dinky and the barycenter will eventually slide into the primary’s radius.

  26. Silber

    @10. allium: Hm, I like Gyges alot. Very meta.

  27. jcj4972

    perhaps its not a moon but a frozen Mass Effect relay!

  28. “We’re running out of good names!”

    Quick, somebody invent more gods!

  29. Duwane

    How can hubble take a picture of a galaxie many many more light years away and it is crystal clear, but it takes a picture of pluto which is reletivly very close and it looks so blury?

  30. Radoo

    This image subtracting technique is used on the images from the IceHunters (Zoouniverse) project.

  31. Tim C

    How about naming the new moon Phil?

  32. Michael Berry

    @20. Mike Richards:

    I like Alecto, a lot. Seconded.

  33. ophu

    How about “Flea”? Pluto has fleas, just ask Mickey. :)

  34. @ 17. Ashley F Miller

    We’ve really almost fully plumbed the Persephone mythology for solar system objects.

    In addition to asteroid 399 Persephone, there was already asteroid 26 Proserpina. Kore (a moon of Jupiter) and Despina (a moon of Neptune) are also taken. The only other name of Persephone left is Nestis.

  35. Howard

    Ashley F. Miller beat me to it. I also say Proserpina.

    Or maybe name it after one of the characters in Dante’s Inferno? Plutus is the guardian of the 4th circle and is often conflated with Pluto; perhaps this would be a reasonable name for the 4th moon of Pluto.

  36. WJM

    When are they gonna find another moon orbiting OUR planet, dammit?

  37. pastronomer

    @16

    I wouldn’t be surprised if there was an Earth sized KBO buried in the avalanche of sensitive WISE data that will be/is available.

  38. OtherRob

    @Duwane, #30. Actually the picture is perfectly clear. It’s just that Pluto is very fuzzy. ;)

  39. spiridonia

    The area around Pluto is getting more and more interesting. I can’t wait till New Horizons gets there.

  40. Julie

    Is it just the perspective of the images, or is Charon orbiting the opposite direction from the other 3 moons?

    @Duwayne — it partially has to do with the focal points of the telescope. Like how a farsighted person can read billboards clearly, but has to hold a book at arm’s length to read it. They can only focus Hubble in so far. I believe exposure times may have something to do with it too, although I’m not 100% certain on that point.

  41. Gary Ansorge

    Cool! Pluto has puppies.

    Gary 7

  42. VinceRN

    The closer we look, the more we find, everywhere in the solar system. We have even been finding rocks out there with orbits (of the Sun) very near Earths. The solar system is a crowded place. I’d bet in 2015 we discover several more objects around Pluto. Uranus has 27 so far, Neptune has 13, why would Pluto only have four? We will soon find that all the mythologies of history combined don’t have enough names for all the things we’ll want to name.

  43. Pete Jackson

    They don’t give a stellar magnitude estimate for P4, but we can estimate. Pluto is 2300 km across, and we’ll assume that the lower figure for the diameter of P4 of 13 km across is for it having the same albedo as Pluto, about 0.6. Then it will be about 31,000 times fainter than Pluto, corresponding to 11.2 magnitudes (2.5 times the base 10 logarithm). Given Pluto has magnitude about 14, then P4 is about magnitude 25. Hubble can see a few magnitudes fainter than this, but not for a faint moving object next to a much brighter one!

    @30 Duwane: The fuzziness of a Hubble picture depends on how much the individual pixels of the detector are blown up in the final picture you see. Nearby galaxies cover many pixels, so their pictures look sharp. The most distant galaxies that Hubble can see look fuzzy like this since they only cover a few pixels.

  44. QuietDesperation

    Running out of names? That’s a bit Eurocentric, Phil. :-)

    There’s all sort of other cultures out their with huge mythologies just *full* of names.

    I, for one, think we need more things out there with names like Tlahuizcalpantecuhtli and Chalchiuhtecolotl.

  45. CB

    @ FoxTrot:

    But I was sincerely hating to break it to you that your view of the past where words meant something, damnit, was a little rosy. But I guess you knew that “planet” and “moon” didn’t mean anything more than “those things [points at sky], which we call planets, and the things around them are moons.” which makes me wonder why you were even looking backwards as if it was better when you know it wasn’t, then?

    Anyway, you’re right about how Pluto never would have been called a planet in the first place if we’d known about the rest of the KB. Unfortunately the example of Ceres doesn’t help much because Ceres didn’t have 70 years to cement itself in popular culture as a planet so there are no emotional attachments to it. So if you bring it up, you’ll probably just get “Well then it should be a planet too” since they don’t care about Ceres either way.

    But really, I like Neil Tyson’s take on the issue, where there’s a bunch of objects, and they have a bunch of different properties, and they should all just be cataloged with those properties and if you’re interested in the objects with some subset of properties, then that’s what you look at. Pluto is in the set of things that orbit the sun and are big enough to be round. It’s not in the set of objects that dominate their orbits. It’s in the set of objects that orbit a point that isn’t inside any of the bodies in the system.

    What you call cross sections of these various properties isn’t really that important to me. As long as we must have names for them, then I do think calling Pluto something different than Saturn or Earth is a good idea since it recognizes that they differ in a couple important properties.

  46. Having just finished Mike Brown’s “How I Killed Pluto and Why It Had It Coming”, I can highly recommend it to readers of this thread. (Including a discussion of “what do words like ‘planet’ really mean?”)

    That said, how about “Curulewski”? Or is that too obscure of a reference? :-)

    BTW, I still find it amusing to find models of the Solar System with 8 planets, which come in a molded plastic shell with room for a ninth, conspicuously empty.

  47. FoxtrotCharlie

    But I was sincerely hating to break it to you that your view of the past where words meant something, damnit, was a little rosy. But I guess you knew that “planet” and “moon” didn’t mean anything more than “those things [points at sky], which we call planets, and the things around them are moons.” which makes me wonder why you were even looking backwards as if it was better when you know it wasn’t, then?

    Of course I knew! I just had no idea… kidding aside, I just have a strange sense of humor. It would have been nice if somehow a nice neat structure could have been set up that highlights the uniquely large and impressive objects of our solar system, but no one ever actually put thought into it. There has never been a need to actually define these things formerly before and actually I don’t really think there currently is one in Astronomy because the majority of them don’t actually care for research purposes. I think the whole IOU fiasco was because Pluto was discovered ahead of its time, and of course a lot of egos and national pride being flaunted and what not.

    In reality all these bodies in space are the same. If it’s large enough it will be spheroid thanks to gravity, if it’s massive enough it will be able to crush atoms in its core and ignite fusion. If it’s supremely dense it will collapse and tear space and suck everything in it including light. I think we will find that instead of having neat categories for astronomical bodies, each will will exist inside a giant sliding spectrum from the tiniest chunk of mass to the largest star.

    The classification problem is not limited to “planets”, stars are problematic because of the lower limit size for Brown dwarves.

  48. @13. Mike – New Horizons will exceed Hubble’s resolution 10 weeks prior to closest approach in July 2015. So, about March or April.

    My own question is one I’m scared to ask: Is New Horizons on Congress’ chopping block? I know they’re trying to piss away the JWST out of some sick hypocritical point about government inefficiency, I guess, but the Pluto mission was already axed once. If they kill this thing while the probe is still in transit I will cry for a week. Anyone have any inside info? Is this mission safe?

  49. Keith Bowden

    “That’s no moon…”

    What? I’m surprised no one had said it yet! :P

  50. QuietDesperation

    Is New Horizons on Congress’ chopping block?

    Hard to imagine what they would chop. The data reception is a trivial matter compared to something still under design/construction. The deep space network is already there. It’s just operational costs from this point on. Google reveals no immediate threats.

    Anyone making a generic sunk costs argument on an in transit probe will be pounded into submission.

  51. [Charon seen shaking tiny fists of rage]

  52. Nebogipfel

    Running out of names? Time to take up Arthur C. Clarke’s suggestion and start on the Hindu pantheon.

  53. andy

    One of my favourite hypotheses about the Pluto system is that there might be a ring system formed by material blasted off the small satellites by impacts. So far there are no known examples of ring systems around solid primaries (unfortunately the proposed ring system around Saturn’s moon Rhea seems to have been disproven by subsequent observations), and a circumbinary ring system would certainly be interesting. Wonder if Nix, Hydra and P4 might act as shepherd satellites.

  54. Obviously it should be called “K.B.” for Kid Brother”

    ( see: http://scienceblogs.com/gregladen/2011/07/yeah_but_how_do_you_pronounce.php )

  55. Floyd

    (Cranky but not yet proven suspicion):
    I suspect that the fundies are the people setting up the New Horizons chopping block. It’s harder to get rid of hundred of various planets that can’t be easily ignored by the religious nuts who really don’t like science at all…especially if life is found on any of those other planets…

  56. Given that Alan Stern is on the discovery team, I’m guessing that the new moon will be named something like Plutoistooaplanetinyourfacemikebrown.

  57. -jeffB

    I have to say that “Pluto is very bright” tripped me up a little bit. :)

  58. Jake

    @Dragonchild – I doubt they would defund a probe that’s 5 years into a 9 year mission, especially one that could provide this much data for scientists and pretty pictures for the public.

  59. Grand Lunar

    “We’re running out of good names!”

    We could always turn toward modern fictional names. Just as good as mythological ones, eh?

    Question is, what name to use?

  60. robkelk

    “Cerberus seems like an obvious choice, but there’s already an asteroid with that name.” That didn’t stop astronomers from using Galatea and Larissa for both moons of Neptune and Main Belt asteroids, so there’s no reason it would stop the IAU from reusing the name here as well.

  61. Clete Orris

    Call it Asshat.

  62. Mark Hansen

    Nebogipfel beat me to it, but what the heck. Rama anyone?

  63. Phil, thanks for bringing me up to speed astronomy news-wise.

    It does seem like we’re running out of Greco-Roman names for new objects, so Hindu names might be very appropriate.

    Rama sounds good.

    I do remember an old hard-SF manga from the 1980s that had a newly discovered giant planet at the edge of the solar system named ‘Lucifer,’ though I forget the title of the series.

  64. Chad

    For a nod to Dante, I hope they name it Phlegyas. It goes with the theme perfectly.

  65. Matthew

    Can we call it Nibiru to freak out the tin foil hat crowd? I want this to happen so bad.

  66. Erp

    Looks like Hel is taken also

    Lethe doesn’t seem to be taken or Styx

    Azrael

  67. Naomi

    Duwane @ 30, a galaxy is slightly larger than Pluto. Just a bit.

    Troythulu @ 63, wasn’t that also the name given to the newly-ignited Jupiter in Odyssey Two? If you remember the name of the series, I’d be interested in reading it!

  68. csrster

    I’d like to see it called Cerberus. There’s already an asteroid with that name but maybe they could just give rename the asteroid. Heel doggy! Heel!

  69. lepton

    Just be nitpicking, 2 photos alone doesn’t make p4 a satellite of Pluto, it can still be a background star. Of course if we also know coordinate of the Pluto in both photos and frame orientation, then, I am sold. :-)

  70. Laurène

    We are NOT running out of greco-roman names, it’s just that Hades doesn’t have that many myths attached to him contrary to his brothers. Indeed Cerberus would have been perfect, and still can, after all they changed the spelling of Nyx to Nix for one of its satellites, so rather than the latin spelling, why not use a spelling “closer” to the greek one, like Kerberos. Or, as pointed out by others, you can name it after one of the rivers of hell, Acheron, Styx, Lethe, Cocytus… or the last judge of hell who is neither an asteroid or a transneptunian object : Aeacus… or even Tartarus, Ascalaphus, Minthe, Theseus, or many many others who are linked to either greek hell, or to the myths attached to the other satellites. In fact, if the people naming asteroids had been more careful they wouldn’t have taken names from greek myths linked too closely to the names of planets or dwarf planets… but there would have been the risk that we would have discovered nothing and that all those great names would not be used… Anyway, I’m sure they will think of a good name, but I hope they will find it before I finish my Ph.D., I already have to change the introduction now…
    Sorry if its a little bit confused sometimes, English is not my mother language.

  71. Messier Tidy Upper

    Whoah! I miss checking the net for a day with Real Life intervening and this happens?! :-o

    This discovery of planet Pluto’s latest moonlet sure came from out of nowhere and is wonderful news. :-)

    Pluto is a planet for me – forever. I consider the IAU definition to be ridiculously fractally wrong, illogical and sizist into the bargain. I redfuse to accpet it or us eitand willalays argue agiants it -because it is just wrong.

    A dwarf planet is no less a real planet than a dwarf star – or a dwarf person – is still a real star (our sun is a dwarf too folks!) or a real person!

    Ceres, Haumea, Eris, Sedna and the others are also planets too – and if that means our solar system has thirty or fifty or a hundred planets in it then so what? The more (planets) the merrier! ;-)

    Names~wise I’m going topint out we already have some level of duplication given that Hydra is both a constellation and the name of one of the Plutonian moonlets. I like the idea of Cereberus as the name for 2011 S/2011 P1* (or just P4 informally) – I also like Styx, Lethe & Hel.

    ————————————–

    * BTW. is that P1 or P4 BA?

  72. Messier Tidy Upper

    @47. Ken B :

    Having just finished Mike Brown’s “How I Killed Pluto and Why It Had It Coming”, I can highly recommend it to readers of this thread. (Including a discussion of “what do words like ‘planet’ really mean?”)

    Seconded – by odd co-incidence I just finished reading that one myself last night. Great read, good bloke :-)

    However, I still totally disagree with him on his eventual conclusion that Pluto ain’t a planet. It is. I’ve already posted numerous times why I think so.

    If Earth or Jupiter orbited where Pluto did – they wouldn’t count as planets either. IF Pluto orbited where Mars did – there owould be no doubt of its planetary status and it would be one of the brighter objects in our sky.

    Pluto is a planet. Full Stop. The IAU can take a long walk off a short jetty if they are silly enough to claim otherwise.

    *****

    In other news Atlantis is home safely and successfully.

  73. CORRECTION for clarity from # 71 :

    I consider the IAU definition to be ridiculously, fractally wrong, illogical and sizeist into the bargain. I refuse to accept it or use it and will always argue against it – because it is just plain wrong. Hopefully (& I fully expect that) this issue will be revisited one day (or one IAU meeting perhaps with new management – when does *that* happen?) and the IAU’s absurd mistake will be corrected preferably sooner rather than later.

    See :

    http://kencroswell.com/PlutoQuestion.html

    &

    http://kencroswell.com/PlutoQuestion2.html

    &

    http://kencroswell.com/NinthRockFromTheSun.html

    via Ken Croswell – who I agree with on this matter – for more.

    My personal definition would be that if an object is :

    1) Gravitationally rounded ie. spherical or ellipsoidal for rapid rotators through it’s own gravity hence NOT an asteroid or comet nucleus.

    2) Never self-luminous via nuclear fusion at its core thus NOT a star or brown dwarf.

    &

    3) NOT directly orbiting another planet and therefore NOT a moon.

    Then it is a planet.

    I believe this definition is simple, clear and most scientifically useful and logical in fullest accord with Occam’s Razor and best at passing the ‘Reductio ad absurdum’ test of logic – key points where the current poor and dubiously motivated Pluto-bashing IAU definition falls down.

    Reghardless of the whole planethood question :

    Congratulations Pluto – great to see another puppy in your litter! :-)

    Raises another beer to toast Pluto’s fourth and smallest moon yet found. :-)

    *****

    PS. Click on my name for an article on the final ever Space Shuttle landing.

  74. The big rocky comet has another rocky comet flying around it. Who knew?

  75. Maria

    @45 While Chalchiuhtecolotl might be a bit of a mouth full for most people, Chalchi or Chal are cute names for this little pup.

  76. ceramicfundamentalist

    Is Pluto unusual among Kuiper Belt objects in the number of satellites it has? It seems so to me, although there may be a strong observational bias happening (more looking=more satellites found). Or could it be that most of the major KBOs have there own little systems of moons and moonlets?

  77. QuietDesperation

    (Cranky but not yet proven suspicion): I suspect that the fundies are the people setting up the New Horizons chopping block. It’s harder to get rid of hundred of various planets that can’t be easily ignored by the religious nuts who really don’t like science at all…especially if life is found on any of those other planets…

    I hope you weren’t serious. I have little use for religion or its more fanatical followers, but that’s just paranoia. Can we keep the skepticism in the real world? For example, there’s a Vatican funded telescope in Arizona that has discovered hundreds of objects beyond Neptune’s orbit.

  78. Chris A.

    @Duwane (#30):
    “How can hubble take a picture of a galaxie many many more light years away and it is crystal clear, but it takes a picture of pluto which is reletivly very close and it looks so blury?”

    It’s all about angular size (that is, how large each object appears). While Pluto is enormously closer to us than a galaxy, it is even more enormously smaller. Specifically, an object’s apparent (angular) size (in radians) is its actual diameter divided by its distance.

    For example, consider the apparent size of a galaxy the size of our Milky Way (100,000 light years across) in the Virgo cluster (60 million light years away). Its angular size is 100,000/60,000,000 = 0.0017 radians = 0.09 degrees. Pluto is 2,390 km wide, and lies roughly 5,900,000,000 km away, so its angular size is 2,390/5,900,000,000 = 0.0000004 radians = 0.00002 degrees. So Pluto appears roughly 4000 times smaller than a Milky Way-sized Virgo cluster galaxy, and thus only comprises a few pixels on Hubble’s CCDs (whereas a large Virgo cluster galaxy is so big it requires a mosaic to get the whole thing).

    @Julie (#41):
    “@Duwayne — it partially has to do with the focal points of the telescope. Like how a farsighted person can read billboards clearly, but has to hold a book at arm’s length to read it. They can only focus Hubble in so far.”

    This is not correct. Hubble’s near focus range is on the order of a few thousand km, not six billion! Hubble images tiny bits of the Earth to make flat fields to calibrate its CCD chips, because clouds 600 km away are sufficiently out of focus to appear uniformly white. On the other hand, Hubble has imaged the moon quite sharply, and the moon is a lot closer than Pluto! In fact, Hubble makes no focus adjustment between Pluto and the most distant galaxies; they are all, practically speaking, at “infinity.”

    “I believe exposure times may have something to do with it too, although I’m not 100% certain on that point.”

    Nope. Pluto (at magnitude 14.0) is very bright for Hubble, and requires a very short exposure to avoid saturating the CCD. And Pluto’s moons (including the new one) are nowhere near as dim as the dimmest objects Hubble has imaged.

  79. Kevin Conod

    So Pluto has a fourth moon. What shall we name it? . . .

    I am rooting for “Xiphion” – named for a wreath of flowers some say Pluto wore.

    (I believe its pronounced “Zifeon”)

  80. Andre

    @Michael: no. EVERY body which orbits another body orbits around their common barycenter. The question is that, in the case of the Earth and Moon, their common barycenter is INSIDE the Earth. In the case of the Earth and Sun, their common barycenter is INSIDE the Sun. But in the case of the Pluto-Charon system, their common barycenter does not lie within either body, but in between them. So we can say that Charon orbits around Pluto at the same time that Pluto orbits around Charon.

  81. andy

    2) Never self-luminous via nuclear fusion at its core thus NOT a star or brown dwarf.

    FAIL. Sorry to have to keep pointing this out to you, but there are quite a few known examples of systems that indicate that the fusion criterion simply does not work as an upper limit on planetary mass. The process that forms planets does not appear to care whether the resultant object can undergo core fusion.

    Applying your definition to, the Upsilon Andromedae system gives the counter-intuitive result that Upsilon Andromedae c, with a mass 14 times that of Jupiter, is not a planet. However it is clearly part of a multiplanet system that happened to form some very massive gas giants. Massive stars appear to be perfectly capable of forming massive planets, for example the 2.7 solar-mass red giant Nu Ophiuchi has a multiplanet system with planets of at least 22 and 24 Jupiter-masses.

    In short, your definition fails to adequately describe the observational data. Back to the drawing board!

  82. hhEb09'1

    @CB#46 “Unfortunately the example of Ceres doesn’t help much because Ceres didn’t have 70 years to cement itself in popular culture as a planet so there are no emotional attachments to it.”

    From the online references that I can find, it was known as a planet for over fifty years, after it was discovered at the start of the nineteenth century.

  83. illexsquid

    This totally ruins my suggestion for a photo of all *four* Pluto-system bodies lined up, on New Horizons’ approach to the flyby, back when the team was soliciting photo-ops.

    BTW, current rules only require unique names for objects in solar orbit; moons don’t count, and indeed, asteroids 106 Dione, 577 Rhea, 593 Titania and others share their names with moons. I liked the Cerberus suggestion, at least until I heard Kevin C’s “Xiphion” above.

  84. Tomalak Geret'kal

    *ahem*

    “Up close *and* personal”!

  85. Kzinti4444

    I agree with Matt Petty- Yuggoth! A great tribute to the author H.P.Lovecraft! Wish I had thought of it myself.

  86. Keith Bowden

    @65 Troythulu

    The series you recall was called 2001 Nights by Yukinobu Hoshino. Great stuff.

    Italian-Americans are Americans. Dwarf-Planets are Planets. :)

    And I nominate Yog-Sothoth for the new moon’s name. ;)

  87. andy

    It’s kind of funny that we had “minor planets” which weren’t planets for ages and ages without any kind of fuss, then as soon as we get “dwarf planets” this kind of thing suddenly becomes horrible and unacceptable…

  88. Kevin Conod

    hh is correct – Ceres was considered a major planetary body for more than 40 years.

  89. For those of you who read Brown’s book, I urge you to also read Alan Boyle’s “The Case for Pluto” to get the other side. It is a fun, easy read, and anyone interested in this topic is likely to enjoy it.

    Ceres should never have been demoted from planet status in the first place. Nineteenth century astronomers’ telescopes could not resolve it into a disk, so there was no way for them to know that unlike almost all other objects in the main belt between Mars and Jupiter, Ceres is spherical, rounded by its own gravity. That makes it a small planet, and the same is true for Pluto. It is important to remember that Alan Stern is the person who coined the term “dwarf planet,” in 1991, with the intention of referring to a third class of planets in addition to terrestrials and jovians–small planets large enough to be rounded by their own gravity but not large enough to gravitationally dominate their orbits. He never intended for dwarf planets to not be considered planets at all.

    While we often think of Pluto as icy, its composition is estimated to be 70-75 percent rock.

    As far as underworld related names for P4, how about Hecate, an underworld goddess in the Greek pantheon, or Kali, the Hindu underworld goddess?

  90. KC

    We have no high resolution images of Ceres yet…”it is rounded”…but how round is “round”? Is an object that is 99% round a planet but one that is 98%, or 97%, not?

  91. Messier Tidy Upper

    @ ^ KC : Actually, there’s a pretty reasonable Hubble image that shows Ceres is indeed round. Looking forward to seeing Dawn‘s view of the “asteroid planet” or 4 and a halfth planet as Isaac Asimov called it though! :-)

    @84. andy :

    FAIL. Sorry to have to keep pointing this out to you, but there are quite a few known examples of systems that indicate that the fusion criterion simply does not work as an upper limit on planetary mass. The process that forms planets does not appear to care whether the resultant object can undergo core fusion. Applying your definition to, the Upsilon Andromedae system gives the counter-intuitive result that Upsilon Andromedae c, with a mass 14 times that of Jupiter, is not a planet. However it is clearly part of a multiplanet system that happened to form some very massive gas giants. Massive stars appear to be perfectly capable of forming massive planets, for example the 2.7 solar-mass red giant Nu Ophiuchi has a multiplanet system with planets of at least 22 and 24 Jupiter-masses. In short, your definition fails to adequately describe the observational data. Back to the drawing board!

    Nah, I don’t think so. I’m quite happy to say that brown dwarfs can form like planets do and orbit stars and still be classed as brown dwarfs.

    If Upsilon Andromedae c shines by core nuclear fusion and would be considered a brown dwarf were it found on its own, why shouldn’t we call still call it a brown dwarf when it happens to orbit a Procyonese type star instead? A stellar system can consist of a star and another star, a star and a planet or planets or a star and a brown dwarf or more or a star and planets and brown dwarfs.

    I don’t think this is a problem. Ultra-super-massive gas giants that overlap with brown dwarfs in their nature get an “upgrade” to brown dwarf class, ice dwarf planets like rock (terretsrial /earthlike) dwarfs are rightly considered as planets in their own right – as they are – and the Jovian and Neptunean mass gas giants remain planets as they also are. Where’s the problem with that?

    @92. Laurel Kornfeld :

    For those of you who read Brown’s book, I urge you to also read Alan Boyle’s “The Case for Pluto” to get the other side. It is a fun, easy read, and anyone interested in this topic is likely to enjoy it.

    Thanks for that recommendation – I hadn’t heard of that and am now very keen to see if I can aquire a copy of it from somewhere. Cheers! :-)

    Ceres should never have been demoted from planet status in the first place. Nineteenth century astronomers’ telescopes could not resolve it into a disk, so there was no way for them to know that unlike almost all other objects in the main belt between Mars and Jupiter, Ceres is spherical, rounded by its own gravity. That makes it a small planet, and the same is true for Pluto. It is important to remember that Alan Stern is the person who coined the term “dwarf planet,” in 1991, with the intention of referring to a third class of planets in addition to terrestrials and jovians–small planets large enough to be rounded by their own gravity but not large enough to gravitationally dominate their orbits. He never intended for dwarf planets to not be considered planets at all.

    Agreed completely and very well said. :-)

    While we often think of Pluto as icy, its composition is estimated to be 70-75 percent rock. As far as underworld related names for P4, how about Hecate, an underworld goddess in the Greek pantheon, or Kali, the Hindu underworld goddess?

    Yes, Hecate sounds like a good name for this latest of the now many Plutonian moons – if it hasn’t already been taken and even if it has! :-)

    Ice dwarfs are rocky as well as icy too – but still icier than the rock dwarfs like Earth which have far less percentage of ice intheir composition. To call them “ice-and-rock dwarfs” starts getting a tad clunky albeit being somewhat more accurate. ;-)

    ————————————

    “… he had left out a planet. It was not his fault; everyone leaves it out. I leave it out myself when I list the nine planets, because it is the four-and-a-halfth planet. I’m referring to Ceres; a small but respectable world that doesn’t deserve the neglect it receives.”
    - Page 63, chapter 5 “The World Ceres” in ‘The Tragedy of the Moon’ by Isaac Asimov, Mercury Press, 1973.

  92. Rift

    “Anyway, you’re right about how Pluto never would have been called a planet in the first place if we’d known about the rest of the KB.”

    Ain’t sure about that. When I was a kid, Mercury was thought to be the smallest planet in the solar system, with Pluto the second smallest. I’ve seen it shrink as we got more and more information about it until it shrank itself out of planet-hood.

    Hindsight is 20/20.

    Clyde Tombaugh did an amazing job finding Pluto. I may be biased, because the University I went to has an observatory named after him. (he attended it too) and I’m good friends with a grandson of his. Neil DeGrasse Tyson was right, in the ‘Pluto Files” when he said it was the world’s favorite planet. And he just told TAM9 to ‘get over it’. Well, no sir. Pluto is grandfather claused in as a planet as far as I’m concerned.

  93. Nigel Depledge

    Duwane (30) said:

    How can hubble take a picture of a galaxie many many more light years away and it is crystal clear, but it takes a picture of pluto which is reletivly very close and it looks so blury?

    Pluto is tiny. The “photo” (for want of a better word) has had to be massively enlarged to we can see Pluto, so much so that we also see individual pixels.

    Galaxies, OTOH, are huge, occupying a far larger piece of the sky. And features that we consider to be sharply-resolved on a picture of a galaxy are usually many tens of light-years across.

    Of course, Hubble has imaged really, really distant galaxies, and these appear as faint little fuzzy blobs.

  94. Julie

    @Chris A– thanks for the correction. =)

  95. andy

    Ultra-super-massive gas giants that overlap with brown dwarfs in their nature get an “upgrade” to brown dwarf class, ice dwarf planets like rock (terretsrial /earthlike) dwarfs are rightly considered as planets in their own right – as they are – and the Jovian and Neptunean mass gas giants remain planets as they also are. Where’s the problem with that?

    The problem is it leads to an unnatural description of the system. Given the configuration, the intuitive description is that Upsilon Andromedae c is the second planet and Upsilon Andromedae d the third. But if you say Ups And c is a brown dwarf not a planet, things become a lot messier (pun on your pseudonym fully intended): is Ups And d the second planet? Or the first circumbinary one? Or what? Neither provides an intuitive description of the system. Allow for the existence of deuterium-burning planets (and the deuterium burning phase will only comprise a relatively short part of the planet’s early history) and the description of the system falls into place and makes a lot more sense.

    Furthermore this split ends up with both terms “planet” and “brown dwarf” referring to two fundamentally different groups of objects: “planet” ends up incorporating the low-mass tail of the stellar mass distribution and a cutoff on the planetary distribution, and “brown dwarf” ends up incorporating both star-like objects and the high-mass tail of the planetary mass distribution. This seems to me to be rather like paraphyletic groups in taxonomy, which are generally frowned-upon these days.

  96. Javon

    surprised nobody suggested the name Thanatos… (Death) ?

  97. Jabjabs

    Why don’t they just name it something stupid for once so that they can confuse people of the future. I proper we call it something like Lawn mower.

  98. KC

    Javon – good one. I seem to recall Thantos had been suggested for Eris.

    @Rift: Should we also grandfather in pi=3.1 because we don’t want the Egyptians to feel bad?

  99. @99. andy :

    MTU : “Ultra-super-massive gas giants that overlap with brown dwarfs in their nature get an “upgrade” to brown dwarf class, ice dwarf planets like rock (terretsrial /earthlike) dwarfs are rightly considered as planets in their own right – as they are – and the Jovian and Neptunean mass gas giants remain planets as they also are. Where’s the problem with that?”

    The problem is it leads to an unnatural description of the system.

    ‘Unnatural’ is an odd and sometimes confusing word. I don’t think it is an “unnatural” description.

    Given the configuration, the intuitive description is that Upsilon Andromedae c is the second planet and Upsilon Andromedae d the third. But if you say Ups And c is a brown dwarf not a planet, things become a lot messier (pun on your pseudonym fully intended): is Ups And d the second planet? Or the first circumbinary one? Or what? Neither provides an intuitive description of the system.

    Okay, I see what you are saying here. My suggestion would be to say that “brown dwarf” in this case is ALSO a type of planet just as we can say that Ceres is a type of asteroid as well as being an ice dwarf planet or our Sun is also a star. Things can be two things at once. That objects can overlap to a certain degree because nature is also messier ( ;-) ) than we’d like at times with distinctions not always being clear-cut.

    Brown dwarfs are intermediate mass objects that span the gap between the smallest stars and largest planets. Thus there are are types of ‘Brown dwarfs’ over various ranges – they come in two spectral classes L and T they evolve in various ways and, yeah, there are many complexities and issues with them. There are high mass brown dwarfs that formed like stars and relatively low-mass brown dwarfs that formed like superjovian planets.

    2M1207A (which famously boasts the first exoplanet directly imaged orbiting it), Teide 1 (the first brown dwarf ever confirmed in 1995 and a member of the Plieades star cluster) and the binary brown dwarfs orbiting Epsilon Indi are examples of high mass brown dwarfs that are more stellar than planetary in nature. Upsilon Andromedae c, AB Pictoris b (another candidate for first directly imaged exoplanet) and SCR 1845-6357 (a very nearby brown dwarf orbiting a red dwarf sun at 4.5 AU, the third closest brown dwarf known) are examples of brown dwarfs that are more planetary than stellar in nature.

    Nature builds objects along a continuum starting with the most massive hypergiant stars down through the least massive brown dwarfs through to the largest superjovian planets and down through the rocky terrrestrial planets like Earth to the ice dwarf planets like Pluto at one end of the ice dwarf spectrum down to Ceres at the other.

    It is hard to draw distinct lines. Sometimes dual classification make sense such as calling Ceres both a planet-variety ice dwarf – and the largest asteroid. Similarly UpsAnd c could be termed a brown dwarf – which it is based on fusing deuterium and mass – *and* an explanet* because of its orbit. We could then say Upsilon Andromedae has 4 exoplanets – and one of those planets is also a brown dwarf. Or that it has three planets and 1 brown dwarf and note that planet c is also brown dwarf that counts as a planet in some contexts too.

    Yes, it is a little messy but that’s life. After all, in physics waves are particles as well! ;-)

    ——-

    * Remember here too that the IAU definition is so bad it is restricted to our solar system alone. By IAU decree NO star other than the Sun has planets at all. Comonsense and common usage would prove that part of their dreadful definition wrong – as well as much else. I predict the IAU verdict against Pluto will be widely ignored and eventually corrected by public demand. Exoplanets are planets too – and so those in the ice dwarf class. :-)

  100. Messier Tidy Upper

    For sources and further info on some of the examples etc. see :

    http://en.wikipedia.org/wiki/Brown_dwarfs

    &

    http://en.wikipedia.org/wiki/Teide_1

    &

    http://en.wikipedia.org/wiki/AB_Pictoris

    Plus a few other sources to follow separately as too many links in one post equals very big trouble here.

  101. Messier Tidy Upper

    See these links too :

    http://stars.astro.illinois.edu/sow/upsand.html

    http://www.universetoday.com/9879/first-direct-image-of-an-exoplanet/

    &

    http://www.space.com/2179-newly-discovered-failed-star-added-stellar-neighborhood.html

    For Upsilon Adromedae, 12M1207A and SCR 1845-6357 frutehr details and sources. Hope this is interesting /helpful for y’all. :-)

  102. andy

    But even that doesn’t work particularly well because there is substantial evidence from open clusters that stars can form below the deuterium fusion limit, so you can get stars of 6 Jupiter masses which never undergo fusion.

    This then leads to a very confused state of affairs.

    Following the observational evidence leads to the conclusion that there are two different populations of objects in the mass range: the low-mass tail of the stellar distribution, which are a natural extension of the brown dwarfs, and the high-mass tail of the planetary distribution, which group naturally with the planets.

    In different environments the distributions change, e.g. for objects in orbit around solar mass stars there appears to be a lack of objects at around ~35 Jupiter masses or so, which may indicate that in that particular environment, the brown dwarf and planetary populations are (for the most part) separated there.

    For 2M1207b the mass ratio essentially rules out a planet-like formation – what we have is a low-mass binary star where one of the two stars is below the fusion limit. These naturally group with the brown dwarfs.

    Distinction based on fusion just leads to unhelpful confusion. Applying both the terms “planet” and “brown dwarf” to the same object obscures the distinction between the two groups of objects which is naturally suggested by the observations.

    In short, going with the observations we see that there is a process of top-down collapse which builds stars, and a process of formation from discs which builds planets. Sometimes the star formation mechanism produces objects which are too small to undergo fusion, sometimes the planet formation process forms objects which are massive enough to do so (just as it doesn’t particularly care about whether the resultant object has a magnetosphere, plate tectonics, a solid surface, satellites, etc).

    The planet formation process results in a small number of massive objects and leaves behind also various reservoirs of objects which never quite made it (e.g. the main asteroid belt, the Jupiter Trojans, the Edgeworth-Kuiper belt and the scattered disc). Objects such as 1 Ceres, 4 Vesta, 136199 Eris and 134340 Pluto are merely the largest objects in the various small-body reservoirs, and are qualitatively distinct from the planets which substantially outmass everything else in their vicinity by several orders of magnitude: for example Jupiter is clearly distinct from the population of small objects that cross its orbit, there is no reasonable argument that it is a member of a belt population.

    Going along these lines, Ups And c is clearly a planet and not a brown dwarf, 2M1207b is clearly a brown dwarf and not a planet, and 134340 Pluto is not a planet but a large member of a belt population. :)

    (Note this is not the IAU definiton either, “not a member of a belt population” is not precisely the same as “cleared its orbit”, and it generalises to exosystems too…)

  103. Mike Kelley

    What Name Would You Pick for Pluto’s Newly-Discovered Moon?http://nasawatch.com/archives/2011/07/what-name-would.html

    “If you had a chance to name this new moon what would you name it – and why did you pick that name? Oh yea, the IAU claims to have a monopoly on naming objects and features in our solar system – and beyond. But there is nothing legally binding to the names they decide to use. Everyone just goes along with them because … well … because. And who gave them this role anyways? Answer: they appoint themselves. So why can’t the rest of us have a say in naming the things in our universe? The IAU is so 20th century. Its time to change this process.”

  104. Tubaka

    How about something Ancient Near Eastern like Mot or Sheol?

  105. @106. andy :

    But even that doesn’t work particularly well because there is substantial evidence from open clusters that stars can form below the deuterium fusion limit, so you can get stars of 6 Jupiter masses which never undergo fusion.

    I’d call those planets that happen to be born in a star-like manner and are free-floatuing in space.

    Is that unreasonable in your view – and if so why?

    This then leads to a very confused state of affairs.

    Uh, like its not already? :roll:

    The IAUdefinitionis more confusing and worse. It’s not a sclear-cut or inclusive as my alternative or many other better ones. We’re having this discussion now because things aren’t now clear.

    Following the observational evidence leads to the conclusion that there are two different populations of objects in the mass range: the low-mass tail of the stellar distribution, which are a natural extension of the brown dwarfs, and the high-mass tail of the planetary distribution, which group naturally with the planets. In different environments the distributions change, e.g. for objects in orbit around solar mass stars there appears to be a lack of objects at around ~35 Jupiter masses or so, which may indicate that in that particular environment, the brown dwarf and planetary populations are (for the most part) separated there.

    Okay, so? Is this set in stone anyhow or just the result of our observations so far which may lead to a bias in what we can and can’t detect?

    For 2M1207b the mass ratio essentially rules out a planet-like formation – what we have is a low-mass binary star where one of the two stars is below the fusion limit. These naturally group with the brown dwarfs.

    Hmm.. not so sure this is true or that we know enough to say given our understanding of planetary formation remains incomplete. The univverse keeps surprising us in this area.

    We do know one object -2M1207b is mor eplanet-like inmass and probably other qualities than star-like whereas for its larger partner tehreverse is the case.

    Distinction based on fusion just leads to unhelpful confusion. Applying both the terms “planet” and “brown dwarf” to the same object obscures the distinction between the two groups of objects which is naturally suggested by the observations.

    I disagree [shrug.]

    Fusion seems a natural and reasonable point of distinction to me here.

    In short, going with the observations we see that there is a process of top-down collapse which builds stars, and a process of formation from discs which builds planets. Sometimes the star formation mechanism produces objects which are too small to undergo fusion, sometimes the planet formation process forms objects which are massive enough to do so (just as it doesn’t particularly care about whether the resultant object has a magnetosphere, plate tectonics, a solid surface, satellites, etc).

    Um, again my resposne is more, okay so?

    Nature builds astronomical objects out of nebulae in a wholerange of sizes. I’m notsur eIunderstand what youare getting at here.

    Some are large and capable of being sel-fluminous by nuclera fusion -we callthese stars.

    Soem are not capable of shining on their own fusion – we call them planets.

    Some are intermediate capable of some brief limitedfusion but notmuch. We call those brown dwarfs.

    The planet formation process results in a small number of massive objects and leaves behind also various reservoirs of objects which never quite made it

    It also builds up some worlds so they are not-so-much “failed stars” as “really successful jupiters” instead!

    (e.g. the main asteroid belt, the Jupiter Trojans, the Edgeworth-Kuiper belt and the scattered disc). Objects such as 1 Ceres, 4 Vesta, 136199 Eris and 134340 Pluto are merely the largest objects in the various small-body reservoirs, and are qualitatively distinct from the planets which substantially outmass everything else in their vicinity by several orders of magnitude: for example Jupiter is clearly distinct from the population of small objects that cross its orbit, there is no reasonable argument that it is a member of a belt population.

    Yes but Jupiter is located in a belt or zone of its fellow gas giants and it is radically different from Earth and Mercury as well! Earthis aplanet -and has more in common with Pluto than it does with Jupiter!

    Let’s just admit that there is a very wide range in types and masses of planet just as there is with stars shall we?

  106. I propose the name Alecto, the daughter of Pluto and one of the Furies, for P4 as it would contain the initials “C.T.” AKA Clyde Tombaugh…

  107. andy

    Yes but Jupiter is located in a belt or zone of its fellow gas giants

    Actually it isn’t.

    There’s a huge distinction between the configuration of Jupiter, Saturn, Uranus and Neptune and the configuration of all the objects in the asteroid belt.

    But hey I guess whatever it takes to make your beloved Pluto a planet again… even if it means rendering the asteroid belt and Kuiper belt a morass of confusion.

    Whatever I see this is going nowhere.

  108. WR

    Why not call it e.g. Moros (engl.: doom, fate), offspring of Nyx , bother of the Moirae (Fates) ?
    If New Horizon finds some more moons, then they could be names after the Moirae.

    This gives IMO a much better reason than the widely propagated CT in Alecto of the “Moon around a real planet not a dwarf planet” folks. Clyde Tombaugh was, is, and will be the discoverer of Pluto. So there is no real need of a tribute to CT.

  109. Matt B.

    I’d go with Styx (I’ve been wondering for a while why they hadn’t already used it), though Thanatos is a good one. We could call it Nox (Night), since it seems to orbit at about the same disance as Nix. That would be fun.

    Rama should be the name of Earth’s “Trojan” asteroid.

  110. J Ascher

    If the name “Styx” isn’t taken, I propose that for Pluto’s newly-discovered companion.

  111. Harold T.

    Since they’ve already used Cerberus, why not use the Greek version Kerberos?

    Or get controversial and confusing and call it Russell’s Teapot? On second thought, save that one for something gaseous that might contain a tempest.

  112. Is it (by total mass) the smallest known five-body system?

    What’s the smallest known four-body system?

    What’s the smallest known three-body system?

  113. Gosh so many requirements which by the way I will NEVER UNDER ANY CIRCUMSTANCES PUT MY NAME ON THE INTERNET SO HA!!!!!

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